Category Rocketing into the Future

The need for a revolutionary air defense fighter led to many other German rocket interceptor designs near the end of the war, as well as an even more bewildering array of advanced propeller planes, jet fighters and intercontinental bombers that are beyond the scope of this book. Even limiting the focus to rocket airplanes results in a lengthy list of concepts.

Junkers came up with the EF127 ‘Walli’, a rather whimsical code name for what was to have been a relatively large, horizontal take-off rocket fighter equipped with a retractable tricycle undercarriage (i. e. one with wheels under the wings and the nose), a take-off weight of 2,960 kg (6,530 pounds), a wingspan of 6.7 meters (22 feet) and an armament comprising a pair of MG 151/20 20-mm cannon and a dozen air-to-air rockets. With two solid propellant take-off assist boosters each delivering a thrust of 10,000 Newton and an HWK 105-509C dual-chamber rocket engine it was predicted to be able to climb to an altitude of 10 km (6 miles) in a mere 75 seconds, which was significantly faster than either the Me 163B or the Me 263. Apart from the boosters it had many similarities with the Me 263, but had a more conventional shape with two straight wings and a tail with horizontal stabilizers.

Then there was the Arado Аг E381 minifighter, of which the first design had a length of just 4.7 meters (15 feet), a wingspan of 4.4 meters (14 feet) and a weight of only 1,200 kg (2,650 pounds). It was to have been carried to altitude slung under an Ar 234 jet bomber, a plane that was actually operational in August 1944. Because the E381 was so small and simple, heating and electrical power would be supplied by the host during the ascent. Communication between the E381 pilot and his colleague in the Ar 234 would be via a telephone link. The E381 was to be released at an altitude of about 1 km (0.6 miles) above the enemy bomber formation to execute its attack in a shallow dive at close to 900 km per hour (560 miles per hour), firing either a single MK 108 cannon or air-to-air missiles. The Walter HWK 109-509C dual-chamber engine would subsequently be ignited to climb for a second attack pass. At that point the E381 would dive and glide to the ground unpowered. It would land using a skid, similar to the Me 163. Then the little plane was designed to be easily dismantled into wing, fuselage and tail units that could be manually loaded onto a truck for return to base.

Due to the limited ground clearance of the E381 when suspended under its carrier plane whilst on the ground, its pilot would lie on his stomach in the cramped cockpit and view through a bubble window in the nose. This prone position would also help him to sustain the high G-forces when making sharp maneuvers at high speeds. Pilots in a conventional sitting position could experience tunnel vision, black-outs (loss of vision) and even loss of consciousness when sharply starting a steep ascent or a tight turn because the centrifugal force would push blood into the lower part of their body, depriving the brain of sufficient oxygen. Similarly, when pilots would suddenly push their planes into a dive the negative G-forces would push blood into the upper part of the body, causing a reddening of his vision known as ‘red-out’. These phenomena were much less trouble when the pilot was in a prone, horizontal position, since there was little vertical distance between his upper and lower body, making it easier for the heart to keep pumping sufficient blood to the brain. Also, the prone position led to a more aerodynamic fuselage shape with a smaller frontal area, reducing drag.

The second design of the E381 was slightly larger and had a weight of 1,270 kg (2,790 pounds). What appears to be the Аг E381 III had a length of 5.7 meters (19 feet), a wingspan of 5.1 meters (17 feet) and a weight of 1,500 kg (3,300 pounds). Instead of a single MK 108 cannon, the third version was armed with six RZ-65 air – to-air rockets that would be fired from the leading edges of the wings. But the E381 project never materialized. After the war, the prone pilot position was tested in the UK using a second, experimental cockpit attached to the nose of a Gloster Meteor F8 jet fighter. For safety, the conventional cockpit was also manned. The tests showed that the prone pilot could endure slightly higher G-levels, but this position proved to be very uncomfortable, to lead to vertigo (a sensation of motion when one is actually stationary) and to seriously limit the pilot’s rear view; the latter being a very serious disadvantage in a dogfight. Furthermore, it would be very difficult to devise a good ejection seat escape mechanism for this awkward position: ejecting forward was not an option because the plane would catch up with the pilot and collide with him. After 55 hours of flight testing, the idea was abandoned. The prone position soon became obsolete after the war anyway thanks to special anti-G suits with inflatable bladders in the trousers: when they experienced negative G-forces in a sitting position, these bladders would quickly inflate to firmly press against the abdomen and legs in order to restrict the draining of blood away from the brain.

Arado also proposed to develop the TEW 16/43-13, a low-wing rocket interceptor that had a wingspan of 8.9 meters (29 feet), a Walter HWK 109-509A engine, and an armament of two MG 151/20 20-mm cannon and two MK 108 30-mm cannon set in its nose. The wings and tailplane were moderately swept back, and the pilot would sit in a conventional upright position. The company also devised the TEW 16/43-15, a combined jet/rocket powered variant in which a jet engine was mounted on top of the (lengthened) fuselage.

In his 1929 book Wege zur Raumschiffahrt (Ways to Spaceflight) Hermann Oberth had contemplated a rocket aircraft built like a tank to fly into an enemy air fleet. It could then use conventional gunfire to destroy targeted planes but he suggested that collision would also be an effective means of attack. By 1943 this dramatic concept started to look like a valid idea to stop Allied bombers, leading Lippisch to suggest a ‘ram rocket’. This would be launched vertically using a liquid propellant engine and solid propellant boosters (like the Natter) and be equipped with a sharp steel nose to slice through a bomber without damaging the ram rocket (or its pilot). In November 1944 the Zeppelin works, famous for building giant airships, had the same idea and proposed the ‘Rammjager’ (Rammer Fighter). Taking off from a jettisonable tricycle carriage, their little plane would be towed aloft by a fighter aircraft and be released near the bombers. The pilot would ignite a single solid propellant Schmidding rocket (similar to the Natter boosters) to accelerate to 970 km per hour (600 miles per hour) and launch his 14 R4M rockets. He was then expected to make a second pass and actually ram his plane through the tail section of a bomber. It was calculated that the Rammjager would slice cleanly through without great loss of speed and stabihty, and survive the collision thanks to its armored cockpit and reinforced fuselage and wings. It would then glide back unpowered and land on a retractable skid. By virtue of not having a liquid propellant rocket engine, the Rammjager was even simpler than the Natter. After towed glide flights in January 1945 an order for sixteen pre-production prototypes was placed. However, US bombers destroyed the Zeppelin factory before their construction could commence.

Another rather ludicrous proposal by Zeppelin was for the ‘Fliegende Panzerfaust’ (Flying Armored Fist, or Flying Bazooka). This was to be an aircraft filled with high explosives to ram and blow up an enemy bomber; the pilot was supposed either to eject just before impact or sacrifice himself to ensure an accurate hit. If possible, the plane would also be equipped with a cannon to shoot down other bombers in advance of the final ramming attack. In line with the need for a very simple and cheap design, it would be powered by six solid propellant rocket motors only. The machine would be towed to altitude, for which it was equipped with a hooked nose connecting to the tail of a regular fighter aircraft. It would have been some 6 meters (20 feet) in length with a wingspan of 4.5 meters (15 feet). The project never got any further than a full-scale mockup that was presented to the SS in January 1945.

Then there was the DFS ‘Eber’ (Boar), a tiny rocket fighter that either an Fw 190 propeller fighter or an Me 262 jet fighter would tow using a long pole, then release some 300 meters (1,000 feet) above the bombers. The Eber would engage a target in a gliding dive utilizing either a single Mk 108 cannon or air-to-air rockets, and then ignite two solid propellant motors that would deliver a thrust of 15,000 Newton for 6 seconds to make a second attack in which it would ram a bomber. The prone pilot would be protected by an armored cockpit and use a special spring-dampened shding seat to soften the 100 G deceleration shock that would result from the collision with a large enemy plane. After the final attack, a parachute would pull the pilot and his seat from the cockpit. At sufficiently low speed, he would jettison the seat and land using his own parachute. The airplane itself was expendable.

The fact that the idea of ramming enemy planes was popular near the end of the war reflects a level of panic in German military planning and an increasing fanatical demand for pilots to sacrifice themselves in defense of their doomed motherland. The Sombold So 344 ‘Rammschussjager’ (Ram-shoot Fighter) was another approach to the ramming plane concept. Rather than ramming a bomber itself, this rocket aircraft would carry a 400 kg (880 pound) warhead on its nose and fire it into the middle of a bomber group using a solid rocket motor built into the bomb. The warhead was fitted with four stabilizing fins and a proximity fuse for automatic detonation when close to an enemy plane. Allied bombers flew in tight formations so that the onboard gunners could provide cover to each other’s planes and work together to bring down attacking fighter planes. The explosion of the warhead released by the So 344 was expected to destroy three of four bombers and open the formation sufficiently for other German fighters to engage individual bombers. The So 344 was expected to join this carnage employing a pair of machine guns.

The So 344 was to be powered by either a single Walter HWK 109-509 engine or a number of solid propellant rocket motors, have a wingspan of 5.7 meters (19 feet) and a take-off weight of 1,350 kg (2,980 pounds). Its cockpit was located well behind the wings, just in front of the vertical and horizontal stabilizers. It was designed to be carried into the air on top of another aircraft, to land employing a skid, and then be dismantled into two sections for transportation by truck back to its base.

Messerschmitt also produced designs for simple towed ramming rocket aircraft. The basic design for the Me P.1103 of July 1944 had its pilot lying prone inside an armored cylinder cockpit. After release from a conventional Bf 109 fighter or even an Me 262 jet fighter tow plane, it would attack at 700 km per hour (435 miles per hour) shooting a single MK 108 30-mm cannon before ramming one of the bombers. A parachute would then pull the pilot and his seat out of the aircraft. Another chute would soft-land the reusable assembly consisting of the armored cockpit, the cannon, and the floor-mounted Walter RI-202 ‘cold’ rocket engine (the same as in the RATO pods used on German bombers) for retrieval. The tail section would be lost, but that was to have been only a simple wooden empennage derived from the VI unmanned flying bomb. Another interesting fact about the Me P.1103 is that it was to have a rearward firing rocket launcher to defend itself from Allied fighters. A design for an alternative P.1103 version of September 1944 shows a sitting pilot looking through a conventional bubble canopy. The Me P.1104 was another Messerschmitt design for a simple towed, rocket propelled defensive interceptor. This one would have had an HWK-109-509A rocket engine (as on the Me 163B) and been equipped with a single MK 108 cannon. The total weight of the fully loaded plane was to be 2,540 kg (5,600 pounds), so its rocket engine should have provided a maximum speed of 800 km per hour (500 miles per hour) and a range of some 90 km (60 miles).

All these concepts for small and cheap rocket propelled fighters were consigned to the archives by the Luftwaffe, which was undoubtedly better news for the pilots who would have been required to fly these rickety death traps than it was for the crews of the Allied bombers. However, some other rocket fighter designs did progress a little further through the development process.

The Focke Wulf ‘Volksjager’ (the People’s Fighter; not to be confused with the Heinkel He 162 ‘Volksjager’ jet fighter) was based on the design for the Та 183 jet fighter. It was to be a defense interceptor with a similar role and mode of operation to the Me 163. It also looked a lot like the Komet, with a Walter HWK 109-509A2 and sharply swept wings mounted mid-fuselage which were to be mostly made of wood. The wingspan would be 4.8 meters (16 feet) and the total length a mere 5.3 meters (17 feet). It would take off from a jettisonable dolly, climb to the enemy bombers and attack using two MK 108 30-mm cannon located in the lower fuselage sides, then glide back unpowered and land on a retractable skid. Unlike the Me 163 (but like the Та 183) it had a horizontal stabihzer mounted on the vertical fin to form a ‘T’ shaped tail. With the addition of four solid propellant strap-on boosters, the Volksjager was intended to reach an altitude of 5.9 km (19,400 feet) in just 60 seconds, and 16.5 km (54,100 feet) in 100 seconds. This was a significantly faster climbing speed than the Komet, which did not have boosters. The maximum speed was expected to be about 1,000 km per hour (620 miles per hour). Three aircraft were under construction when the war ended but none ever flew. As was the case for the He 162 jet that was also called the ‘People’s Fighter’, the Focke Wulf was probably meant to be flown by relatively untrained pilots recruited from the Hitlerjugend, the Nazi youth movement. But the He 162 proved too difficult for amateurs to fly, and this would probably also have been the case for the Focke Wulf rocket interceptor.

Another Focke Wulf design was the Та 283, an airplane with a slender fuselage, wings swept back at 45 degrees, and two large ramjet engines. Since ramjets do not work at low speeds, for take-off the aircraft was to have a single Walter HWK 109- 509A rocket engine and about 30 seconds worth of rocket propellant. To prevent the big ramjets from disturbing the airflow over the wings, they were to be mounted on the sharply swept tailplane. The armament was envisaged to comprise two MK 108 cannon. When this concept was judged lacking in performance an improved design was proposed in which the fuselage intended for the Fw 252 jet fighter would have a small jet engine emplaced in the central fuselage, two ramjets on the tailplane and a Walter HWK 109-509A just beneath the tail boom. This design was so preliminary that it didn’t even have a proper designation, but after the war it came to be known as the Fw 252 ‘Super Lorin’ (after the inventor of the ramjet concept, Frenchman Rene Lorin).

Heinkel’s contribution to the mixed bag of radical rocket fighter concepts was the P.1077 ‘Julia’. As designed in August 1944, the wooden Julia would have been 6.98 meters (22.9 feet) long, had straight shoulder-mounted wings with a total span of 4.6 meters (15 feet) and a tail with twin vertical stabilizers. Its propulsion was to have been one Walter HWK 109-509C engine with separate combustion chambers for the initial climb and subsequent cruise, and two booster rockets mounted on either side of the fuselage. It would have had two MK 108 cannon housed in blisters on the sides of the forward fuselage. It was initially envisaged that the pilot would fly in a
prone position but an alternative design was prepared in which he would sit in a conventional manner. Like its Bachem Natter competitor, the Julia would have been launched vertically off the ground, but after the attack the pilot would have landed it on a retractable skid rather than bail out. In September 1944 the RLM ordered 20 Julia prototypes and then two weeks later demanded the production of 300 operational aircraft per month. Nothing came of this, of course. Only towing trials with a full-scale mockup were performed before it was destroyed when the Vienna woodworks was bombed, and the Schaffer company in Linz had time only to start two unpowered prototypes, neither of which was completed.

The DFS 346 of the German Institute for Sailplane Flight was not intended for combat, it was designed purely as an experimental research plane. Its chief designer, Felix Kracht, gave it wings swept back at 45 degrees, a streamlined fuselage with a prone pilot, and an HWK 109-509C rocket engine. It was to be taken to high altitude by a Domier Do 217 bomber and then air-launched, a novel concept which, it was hoped, would save the DFS 346 sufficient propellant (otherwise needed for take-off and ascent) to break the sound barrier. The altitude provided by the carrier plane also resulted in lower aerodynamic drag due to the thinner atmosphere and meant Mach 1 could be reached at a lower absolute flight speed since the speed of sound is lower in the colder high-altitude air. The pilot was in a pressurized section that formed a self-contained escape capsule which could be separated from the plane in an emergency. Stabilized by a small parachute, the capsule would fall to an altitude of about 3 km (10,000 feet) where the air pressure is safe, the Plexiglas nose section would separate and the pilot would slide out and land using his parachute. The unfinished DFS 346 prototype was captured by the Soviets at the end of the war, taken to Russia, rebuilt and actually flown (we will discuss this further in a later chapter).

The concept of air-launching was later adopted in the USA for the world’s first supersonic rocket plane, the post-war X-l. The highly swept wings of the DFS 346 were actually much more advanced than the conventional straight wings of the X-l and make the DFS 346 look more like a modern supersonic fighter than the famous

American rocket plane which relied upon brute rocket power and sturdy wings rather than sophisticated aerodynamics to blast through the sound barrier.

Felix Kracht also designed the DFS 228 rocket propelled reconnaissance aircraft, a fairly conventional sailplane design with long, slender but straight wings spanning 17.6 meters (57.7 feet). It was to have a dry weight of 1,350 kg (9,280 pounds) and a take-off weight of 4,210 kg (2,980 pounds). It would be air-launched from on top of a Do 217, be powered by a Walter rocket motor, and land using a belly-mounted skid. The pilot was to be prone in a pressurized escape capsule. The long wings were designed to enable the plane to achieve a cruise altitude of 24 km (80,000 feet), safe from interception by Allied fighters. Its maximum speed was estimated to be about 900 km per hour (560 miles per hour). The mission profile was for a powered climb followed by a slow, unpowered descending glide, then reigniting the rocket motor to climb back to altitude, and so on until the propellant was finished. The resulting saw­tooth flight pattern that would give the aircraft the relatively long range of 1,050 km (655 miles) also prompted its nickname of ‘Sagefish’ (Sawfish).

Walter designed a new rocket motor for the plane because the requirement for a very streamlined fuselage in combination with weight balance made it necessary to place the motor near the plane’s center of gravity, which required fitting a long thrust tube to the tail. The resulting motor was an elongated version of the single­chamber HWK 109-509A2 named the HWK 109-509D. The DFS built three prototypes: VI, V2 and V3. The DFS 228 VI had a conventional seat but it was shghtly inclined to the rear to accommodate the fuselage streamlining and to assist the pilot in handling high G-loads (a similar idea was introduced in the F-16 fighter jet several decades later). The VI made several unpowered glide flights after being carried to altitude on top of a Do 217, and was later fitted with the HWK 109-509D for ground tests. This prototype was captured by the Americans at the end of the war and in 1946 was sent to Britain for study, but it arrived in very bad condition and was apparently scrapped. The V2 had a cockpit with a prone pilot position and apparently made several glide flights before being damaged in a landing accident. The V3 was never finished. None of these aircraft ever flew under rocket power.

Rather than develop a completely new aircraft, in mid-July 1943 Arado proposed to produce a high-altitude reconnaissance rocket plane by modifying the Ar 234 jet, which had made its first flight in June. In the initial design the two jet engines were to be replaced by two HWK 109-509A rocket engine pods. The resulting Ar 234R ‘Hohenaufklarer’ (High-altitude Scout) would be able to take off by itself, ascend to an altitude of 16.5 km (54,000 feet) and photograph its targets while descending in a shallow glide. It would be equipped with the pressurized cockpit already created for the Ar 234C reconnaissance jet. A later design had a dual-chamber HKW 109-509C built into the tail instead of pods slung under the wings. This version was to be towed to an altitude of 8 km (26,000 feet) by a Heinkel He 177 bomber (a large, long-range bomber then under development) and upon being released it would boost itself up to 18 km (59,000 feet). The Ar 234R would be able to photograph areas some 250 km (155 miles) from its base, being towed 200 km (125 km) towards its target and flying a further 50 km (30 miles) on rocket power. The plane would subsequently glide over its targets, igniting the rocket engine at intervals to maintain sufficient altitude.

Freed from the need to mount engines under the wings, a special highly efficient wing was designed to give the aircraft a glide angle of 1 to 14 (in which it would lose 1 meter of altitude for each 14 meters of horizontal flight), sufficient to enable it to glide the entire 250 km (155 miles) back to base.

Another Ar 234 variant fitted with a rocket engine was actually under construction when the Allies captured the factory in which it was being assembled. It consisted of an Ar 234B fuselage equipped with a new concave-curved swept wing optimized for high-speed flight. It was powered by a pair of BMW 003R engines, each consisting of a BMW 003 turbojet with a BMW 718 liquid propellant rocket engine mounted on top. The fact that the pumps for the rocket propellant were powered by the jet engine resulted in a nicely compact assembly. The rocket engine could deliver an additional 10,000 Newton of thrust for 3 minutes during take-off and ascent. Unfortunately the prototype was scrapped.

The sole surviving Ar 234B can be seen in the National Air and Space Museum’s Steven F. Udvar-Hazy Center near Washington Dulles International Airport. It is the basic jet type with a pair of Walter RI-202 ‘cold’ RATO pods under its wings. The parachute pack intended to retrieve the pods following jettisoning soon after take-off can be clearly seen on these examples.

Another pragmatic design enhanced the standard Me 262 jet fighter (which had a jet engine under each wing) with an additional rocket engine. To test the principle an Me 262 was adapted to accommodate a redesigned HWK 109-509A2 motor with the combustion chamber installed in the tail; a portion of the lower part of the rudder was cut away to make room for the nozzle and the rocket exhaust. This Me 262 C-la ‘Heimatschiitzer Г (Home Defender I) prototype made its first rocket assisted take­off on 27 February 1945. The combined thrust from the two jets and the single rocket reduced the take-off run by at least 200 meters (660 feet) and pushed the plane to an altitude of 8 km (26,000 feet) in about 3 minutes (about half the time required by a standard Me 262 and similar to the Me 163 Komet’s performance). Major Heinz Bar later managed to intercept and shoot down an American P-47 Thunderbolt fighter in the rocket propelled test plane by climbing to about 9 km (30,000 feet) in a little over 3 minutes.

A similar concept was the Me 262 C-lb ‘Heimatschiitzer IF which was provided with two BMW 003R combined jet-rocket engines for boosted thrust. Only a single prototype was built and its only flight with the combined propulsion was made on 26 March 1945. This engine was also to have been mounted on an He 162 ‘Volksjager’ (People’s Fighter), the standard version of which had a single BMW 003 jet engine on its back. However, the creation of this He 162E prototype could not be achieved before the war ended.

Despite the success of the ‘Heimatschiitzer Г it was judged that the rocket engine added too much complexity to the jet fighter, making it more difficult to maintain. In addition, the tanks needed for the less propellant-economic rocket severely reduced the available space for fuel for the jet engines, which limited the range and flight duration of the fighter in comparison to a standard Me 262 (issues that would also plague the post-war mixed-power interceptor designs that we will discuss later). These considerations led to the design of the ‘Heimatschiitzer IIP which had a rocket engine bolted onto the belly of the aircraft and its propellant in drop tanks that would be jettisoned once they were empty so that the plane would not be burdened by their useless weight and aerodynamic drag. The advantages of this arrangement were that it required fewer modifications of the standard Me 262, and the modified Me 262 could take off without the rocket engine if it were not needed. Another plus was that maintenance of the rocket system could be separated from maintenance of the aircraft: a fighter would not be grounded by a malfunctioning rocket engine, but could be quickly fitted with a replacement engine while the faulty unit was taken to the repair shop (an idea which, after the war, would be applied to the French Mirage rocket-motor equipped fighters).

Walter designed a powerful ‘hot’ engine based on his HWK 109-509 series for the ‘Heimatschiitzer IV’. This HWK 109-509 S2 gave a thrust of 20,000 Newton and weighed just 140 kg (310 pounds). The engine was to be mounted on the belly of the plane, just behind the roots of the wings. Two jettisonable tanks would be carried externally on bomb attachment points under the nose, with flexible hoses delivering a total of 1,200 liters of T-Stoff to the Walter motor. The C-Stoff would be carried in the rearmost converted fuselage tank. This was designated the Me 262 C-3 and work on the prototypes started in January 1945. Tests on the Т-Stoff tanks apparently revealed a problem with feeding fuel when the drop tanks were mounted lower than the rocket motor. In April the Allies overran the factory at Jenbach before a single prototype could be completed.

Eugen Sanger’s design for the ‘Silbervogel’ (Silverbird) intercontinental bomber surely ranks as the most ambitious of Nazi Germany’s rocket plane concepts. It was the first, more or less realistic design for an aircraft capable of flying on the edge of space and it is therefore described in more detail in a following chapter.

Germany hoped that its superior rocket and jet airplane technology would counter the vast numbers of conventional planes that were being manufactured by Americans in their secure homeland. Given a bit more time, this might have worked at least for a while and greatly prolonged the war in Europe. The Luftwaffe might have been able to put some really revolutionary aircraft into the skies, and a German rocket aircraft would likely have been the first to exceed the speed of sound. However, by the time the ‘wonder weapon’ airplanes received proper support it was already too late, and in any case the developments were too scattered, rivalry between the military services too disruptive, and the constraints in terms of material and propellant availability too great. Some of the small interceptors relied on Arado jet carrier planes that were not themselves available, and those meant to be towed behind conventional bombers and fighters would have been vulnerable to enemy fighters during the first phase of their mission due to the low speed of the towing operation. Many of the RLM designs now seem to be more the results of desperation and wishful (albeit creative) thinking than the reality of military operations. Nevertheless many post-war airplane designs were strongly influenced by some of the more brilliant German developments, particularly the Me 163 and Me 263.

Even before the X-15 took to the air the Air Force, NACA and North American were making plans for an orbital version. This X-15B would be launched using a multi-stage rocket derived from the launch booster of the SM-64 Navaho missile; a project that had just been canceled and had left North American with a warehouse of rocket boosters. But the X-15B was canceled when Project Mercury was approved, a much simpler capsule concept that promised early results in the developing space race with the Soviets. Then the national goal of being first to land a man on the Moon gave rise to the Gemini and Apollo capsule-style spacecraft.

However, the Air Force, regarding a capsule as merely a step on the way to more routine access to space, saw the benefit of a reusable shuttle-type vehicle for manned missions. During the 1950s Werner von Braun had proposed a reusable canard space glider to be launched atop a rocket using two expendable stages. This was explained in Collier’s magazine in 1952, in one of a series of articles on future spaceflight that von Braun wrote with Willy Ley between 1952 and 1954. Collier’s printed 4 milhon copies per issue, so these articles did much to spur enthusiasm for spaceflight in the US. The articles were enlivened by beautifully detailed illustrations by leading space artists, including Chesley Bonestell, that effectively dramatized von Braun’s manned spaceflight development blueprint for the general public. Further publicity came soon afterwards with von Braun presenting a hugely popular three-part Disney television show on the future of space travel, which also featured his designs. At one point von Braun presents his winged spacecraft design: “Now here is my design for a four-stage orbital rocketship. First we would design and build the fourth stage and then tow it into the air to test it as glider. This is the section that must ultimately return the men to the Earth safely.” His ‘Ferry Rocket’ is basically an upper rocket stage with multiple engines and long, slightly swept-back wings, each with an elongated vertical stabilizer mid-way. Large horizontal stabilizers were fitted to the nose, resulting in a canard design. The launcher’s first stage had huge fins as well, not for flying but for counteracting the imbalance caused by the rocket glider’s wings on top of the rocket, as otherwise a slight wind during take-off or buffeting while ascending through the atmosphere would easily blow the whole assembly off course.

By 1959 the Air Force was promoting a new program as the means of performing military manned space missions. Like von Braun’s concept, this ‘Dyna-Soar’ would not be a real rocket plane but a reusable space glider (its name was a contraction of Dynamic Soaring) bolted to the nose of a conventional launch rocket. It would only use its wings during the unpowered descent back through the atmosphere and make a controlled landing near its launch site. There it would be quickly readied for its next launch on a new expendable rocket. In its operational form Dyna-Soar would be able to perform all kinds of missions and even put things into orbit because it would have a cargo bay; it was basically to be a small, early version of the Space Shuttle.

In contrast, Mercury and the later Gemini and Apollo spacecraft were completely single-use; very Uttle of what was launched would come back, and with their ablative heat shields that burned away during re-entry the capsules were not reusable. They also had very little means of maneuvering once they started their ballistic fall back to Earth and at best could be expected to land within a radius of several kilometers of a specific point. Because of this uncertainty in the landing spot, as well as to ensure a soft landing, they had to come down in the ocean, which meant a fleet of search and recovery ships was required. The X-20 pilot would fly his craft back to its airbase, making the return much more economical. Of course a controllable, winged machine was also much more appealing to the Air Force than a ‘spam-in-a-can’ capsule using parachutes. It facilitated a dignified landing on a runway, rather than an inglorious splash into the ocean.

The Air Force forecast numerous versions and missions for the X-20, involving payloads for gathering aerodynamic flight data, satellite inspection, electronic and photographic intelligence, and even dropping nuclear bombs with greater precision than was possible using a balhstic missile! Dyna-Soar was to be a research aircraft, spy plane, orbital bomber and transportation shuttle all in one.

In June 1959 Boeing was awarded the development contract. Boeing’s design was a 5,200 kg (11,400 pounds) delta-winged vehicle with large vertical winglets instead of a more conventional tail for lateral (yaw) control. Most of the internal structure as well as the upper surface was to be made from Rene 41, a ‘super alloy’ that was able to withstand extreme temperatures. However this material would not suffice for the areas that would see the highest temperatures during re-entry, when slamming into the atmosphere at some 28,000 km per hour (17,000 miles per hour), or Mach 28. Capsule spacecraft solved this issue by using expendable ablative heat shields, but as the X-20 was to be a completely reusable space glider its underside would require to be made by placing molybdenum sheets over insulated Rene 41, while its nose-cone was to be made from pure graphite incorporating zirconia rods.

The X-20 would be controlled by a single pilot. Behind him was an equipment bay that could contain either data-collection equipment, reconnaissance equipment, weapons, or seats for up to another four astronauts. The X-20 would be connected to a small rocket stage to enable the craft to shoot itself away from the Titan III booster during launch in case of an abort or, once in space, to change its orbit. At the end of a mission this ‘transition stage’ would fire its main rocket engines against the velocity vector so that the X-20 would fall back to Earth. It would then be jettisoned and the aircraft would descend through the atmosphere and use aerodynamic drag to further slow down (‘aerobraking’). During the initial, high-temperature re-entry, the pilot’s windows would be protected by an opaque heat shield that could be jettisoned once the aerothermodynamic onslaught was over. Because rubber tires would burn during re-entry, the X-20 would land using wire-brush skids made of Rene 41. The Titan III

launcher would be based on the Titan intercontinental ballistic missile and be fitted with exceptionally large stabilizing fins to compensate for the disturbances caused by the X-20’s wings on top of the assembly during ascent through the atmosphere.

In April 1960 seven astronauts were secretly chosen to fly the X-20, among them (future) X-15 pilots Neil Armstrong, Bill Dana, Pete Knight and Milt Thompson.

But the X-20 Dyna-Soar never made it out of the factory, let alone into orbit. In the early 1960s it was already becoming evident that many of its foreseen missions could be performed sooner and more cheaply by unmanned spacecraft or manned capsules. The high cost and questionable military utility led to the cancellation of the program in December 1963. This made sense at the time in terms of immediate technological and military priorities, but in hindsight it is definitely a pity. Although the X-20 was a vertically-launched reusable glider with some orbital maneuvering capabihty rather than a real rocket plane, it was a logical next step in the evolution of rocket aircraft. The X-15 was a true rocket plane, but suborbital. It could reach orbital altitudes but lacked the propellant to accelerate to orbital speed. With the X – 20 the Air Force was developing the technology needed to fly a plane from orbit back to Earth, with all the aerodynamic and thermodynamic complications, and some new materials capable of withstanding extreme temperatures. Had the X-20 continued, it would have delivered valuable experience that could have made the later Space Shuttle a more economical launch vehicle and perhaps opened the way to fully reusable spaceplanes.

Conceptually, a follow-on to the X-20 could have been to replace the expendable launching rocket with a reusable rocket powered carrier aircraft to create a two-stage rocket plane (similar to the X-15B/Valkyrie combination but with the carrier aircraft able to fly higher and faster than the Valkyrie, and with the secondary vehicle able to

boost itself into orbit). That would have been considerably simpler than developing a single-stage rocket spaceplane, whilst retaining the benefits of an all-reusable system with (hopefully) aircraft-like operations. Prior to the cancellation of the X-20 there were many outline designs for orbital rocket plane and shuttle-type vehicles, most of them involving multiple stages. There were all kinds of combinations: orbital gliders with or without integrated rocket stages; with expendable or reusable, winged or non-winged stages using either liquid or solid propellants; and with horizontal or vertical take-offs.

Martin offered the very ambitious ‘Astroplane’, a horizontal-take-off, horizontal­landing, single stage spaceplane which, powered by “nuclear magnetohydrodynamic engines”, sounds like something straight out of Star Trek. This intriguing propulsion system would extract nitrogen from the atmosphere, rapidly cool it, then accelerate the resulting liquid using powerful electromagnetic forces generated by an onboard nuclear reactor. The vehicle had a long, slim shape that would have been perfect for low drag at high speed but unsuitable for horizontal runway landings at reasonable speeds. The designers therefore envisaged deployable wings that would be extended at low speeds to provide additional lift. The bat-like airfoils would be composed of rigid ribs with a flexible membrane stretched between them. What would happen if a wing failed to deploy properly and this flying radiation hazard fell out of the sky was obviously something that would have to be worked on a bit.

In general, however, it was understood that without resorting to exotic, far­fetched propulsion systems, a reusable launcher would have to be a multi-stage vehicle. For conventional multi-stage expendable launchers the useful payload that can be placed into orbit typically represents only 3% of the total weight of the rocket that leaves the pad, and around 18% in terms of hardware (i. e. without propellant). A single-stage vehicle cannot shed the weight of empty tanks and no-longer-needed rocket engines on the way up, so its payload is necessarily considerably less than for a multi-stage launcher. The wings, heat shields and control systems that are required to enable a single-stage vehicle to return to Earth can all too easily reduce its payload to zero, or even to negative values implying the vehicle will not even be able to reach orbit. To compensate, Single Stage To Orbit (SSTO) vehicles must carry more propellant per unit of hardware, which leads to larger vehicles. All this makes the development of a single-stage spaceplane with a reasonable payload extremely challenging, expensive and risky, and certainly beyond the technology of the 1960s and 1970s (and indeed beyond today’s technical capabilities; more on this later in this book).

The Martin ‘Astrorocket’ concept studied in the early 1960s therefore consisted of two vertically launched, winged rocket stages mated belly to belly. The task of the larger vehicle was to get its smaller sibling to high altitude and high speed, release it and then glide back to Earth while the second stage continued into orbit. The orbital vehicle would later make a gliding return (very much like the Space Shuttle) and be reunited with the first stage and prepared for another mission. This VTHL (Vertical Take-off and Horizontal Landing) concept would be proposed many times in various forms and by several different companies.

Douglas offered the ‘Astro’ design. This was based on the same idea but with the orbital vehicle mounted on the nose of the carrier booster rather than attached to its belly, and with both vehicles having lifting body configurations.

Lockheed’s ‘Reusable Orbital Carrier’, which was studied at about the same time, also involved two winged rockets but this combination would take off horizontally using an accelerated sled. The orbital vehicle of this HTHL (Horizontal Take-off and Horizontal Landing) launcher would ride on the back of its large carrier stage, which would use jet engines to return to its launch base. Interestingly NASA had stated in the specifications for this carrier stage that it “should offer a potential commercial application in the late 1970s, such as operating the vehicle over global distances for surface-to-surface transport of cargo and personnel”. In other words, it must be able to be converted into a hypersonic, rocket propelled airliner; a kind of super – Concorde similar to that proposed by Max Valier in the 1930s.

Lockheed and North American both had similar concepts for three instead of two winged stages, which meant more complicated operations but less stringent vehicle mass-minimization requirements. A proposed further development of Lockheed’s ‘System ІІГ would involve a giant first stage booster aircraft with ramjet propulsion and was called ‘System IV’ (System I was the Apollo Saturn IB combination as later used on the Apollo 7 mission, while System II would consist of a Saturn IB rocket with a reusable 10-man spaceplane that would also form the basis for the System III and System IV orbital stages).

In the mid-1960s NASA, along with the Department of Defense, adopted a similar phased approach involving a ‘Class ІІГ vehicle based on the Lockheed’s System IV design but with a hypersonic booster aircraft powered by combined turbofan-ramjet-scramjet engines. Such engines would run as regular turbojets at subsonic and low supersonic speeds, and as ramjets at supersonic velocities where the airstream could still be slowed down to subsonic speeds; at hypersonic flying velocities the airflow through the engine would be supersonic and so the engines would go into scramjet mode. A scramjet (meaning ‘supersonic combustion ramjet’) is a ramjet in which the combustion takes place in a supersonic airflow so that the air coming into the engine does not need to be slowed down to subsonic speeds (as is required for ramjets). The big benefit is that the incoming air does not lose useful energy due to deceleration, energy that would otherwise be converted into heat that would require the engine to be actively cooled. The combined engine system NASA envisaged represented an enormous technological challenge: at the time the only existing hybrid jet engine was the J58 of the SR-71 Blackbird, whose turbojet and ramjet modes enabled the aircraft to reach about Mach 3.2. The hypersonic stage of the Class III vehicle would require to fly much faster and its engine would be considerably more complicated. The joint Aeronautics and Astronautics Coordinat­ing Board Subpanel on Reusable Launch Vehicle Technology, formed by NASA and the Department of Defense, concluded that the required technology could not be expected to be operational before 1982. (In fact, it still does not exist today.) Preliminary calculations for the Class III carrier vehicle indicated it would weigh

306,0 kg (675,000 pounds) at liftoff, if required to carry a 132,000 kg (290,000 pound) orbiter plane with a 16,000 kg (35,000 pound) low-Earth-orbit payload. This meant the total liftoff weight would have been about a quarter of that of the Space Shuttle for a payload only about one-third less. Of course the Space Shuttle actually flew whereas this Class III vehicle remained a paper study so we must be wary of such comparisons. Nevertheless, the numbers do indicate the potential mass benefits to be gained by using airbreathing engines.

A concept called ‘Mustard’ (Multi-Unit Space Transport And Recovery Device) was studied by the British Aircraft Corporation (ВАС) in the mid-1960s. It involved three similar winged vehicles that would be launched vertically as a single stack. A number of configurations were examined: a belly-to-belly-to-back sandwich, triangular belly-to-belly, two belly-to-belly and the third inline on top. Two of the vehicles would serve as boosters to put the third one into orbit, with the boosters pumping their remaining propellant into the orbital vehicle to top up its tanks prior to separation. In this way all of the engines could fire simultaneously for the first phase of the flight, yet the orbital shuttle would still initiate its solo flight with a full propellant load. The concept would potentially have enabled the orbiter to reach the Moon, which is a unique capability for a winged reusable design. All three stages

would have flown back to base after their mission, landing horizontally to be readied for the next launch. Around this same time the Warton Division of ВАС also studied several launch vehicle concepts in which a very large hypersonic aircraft carried on its back a small shuttle mounted on top of an expendable rocket. The ‘European Space Transporter’, which originated as the Nord Aviation Mistral and was studied by French and West German aerospace companies, was rather similar; it looked like a giant airbreathing fighter with enormous ramjet intakes and a rocket propelled lifting-body shuttle strapped onto its belly. Dassault’s ‘Aerospace Transporter’ was also based on essentially the same idea, involving an orbital ‘space taxi’ shuttle carried under a turboramjet Mach 4 aircraft that resembled the Concorde. Dropping a rocket vehicle rather than (as envisaged for the X-15A-3) launching it from the back of a carrier aircraft reduces the risk of the shuttle striking its motherplane, but the downside is a longer and more complex undercarriage on the carrier in order to give the shuttle enough clearance above the ground during take-off and aborted landings of the aircraft combination.

In 1967-1968, the US Air Force awarded several study contracts for an ‘Integral Launch and Re-entry Vehicle’ (ILRV) which would consist of a reusable single-stage VTHL that would jettison relatively inexpensive propellant tanks. This represented a compromise between a fully reusable single-stage launch vehicle (which would be large, heavy and extremely challenging and expensive to create) and a fully reusable two-stage vehicle (that would require the development and operation of two separate vehicles). The McDonnell-Douglas ILRV design featured a VTHL lifting body that resembled a steam iron, mated to four jettisonable tanks: two large ones for liquid hydrogen and two smaller ones for liquid oxygen. It would fold out small wings to increase its lift over drag ratio in the final descent and landing. Lockheed’s proposed ‘Starclipper’ was a VTHL lifting body design in which a single integrated A-shaped propellant tank would ‘wrap around’ the reusable lifting body. General Dynamics proposed a ‘Triamese’ solution with three reusable rocket stages which had fold-out wings and jet engines to land using a standard airport runway. The concept did partly satisfy the ILRV concept of a single vehicle design because the three winged stages would have been virtually identical.

The primary mission of all these reusable spaceplane concepts dreamed up in the 1960s was to transport crews to a large Earth orbiting space station. However, other missions such as the launching, inspection, repair and retrieval of satellites were also envisaged. The reusability was expected to translate into very low operating costs: for instance Lockheed claimed that their Starclipper would have a turn-around time (the time necessary to prepare the vehicle for its next mission) of only 24 hours and would reduce the costs of launching cargo into space to less then $100 per kg in 2011 terms. In fact, launching satellites into low orbit currently still costs $10,000 per kg for expendable launchers (and double this for the Space Shuttle when it was retired that year).

By mid-1969 NASA was planning an extremely ambitious and financially rather unrealistic, manned space exploration program to follow up on Apollo. The wish list included space stations, interplanetary ‘space tugs’ and eventually bases on the Moon and Mars. The first task was to build a 12-person space station in orbit by 1975 and to expand this into a 50-person ‘space base’ by 1980. Smaller ‘way-stations’ would then be deployed in geostationary Earth orbit and around the Moon and Mars. Naturally all this infrastructure would require an efficient, dependable and inexpensive means of transportation in the form of a space shuttle.

In a meeting in April 1969 Maxime Faget, the renowned designer of the Mercury capsule and by then director of engineering and development at NASA’s Manned Spacecraft Center, presented a balsa-framed, paper-skinned airplane model that had short, straight wings and a shark-style nose. It looked remarkably similar to Sanger’s Silbervogel concept of the Second World War. When introducing the design, Faget explained, “We’re going to build America’s next spacecraft. It’s going to launch like a spacecraft; it’s going to land like a plane.”

Back in January NASA had awarded four Phase-А study contracts to McDonnell-Douglas, North American Rockwell, Lockheed and General Dynamics to begin the development of the shuttle launch system. Martin Marietta, whose bid had been rejected, decided to participate using its own funds in order not to be left out of what promised to be a very lucrative project. The NASA requirements called for a vehicle able to launch 12 people as well as some 11,300 kg (25,000 pounds) of supplies to a space station in low orbit. Soon these became even more demanding and complex when it was decided that the vehicle must also be capable of launching satellites and interplanetary probes. Then the Air Force demanded that the stated payload capacity be doubled.

NASA had by then decided that the shuttle was going to be a fully reusable YTHL Two Stage To Orbit (TSTO) vehicle, since that was expected to produce the lowest cost per flight and highest payload capability in combination with good operability and mission flexibility. This meant the next generation launch vehicle was not going to be a real single-stage spaceplane but rather a combination of vertically launched winged rocket stages, each capable of gliding back to Earth and making a horizontal, unpowered landing. In an article optimistically titled ‘The Spaceplane That Can Put YOU in Orbit’ in the July 1970 issue of Popular Science, Wernher von Braun (at the time NASA Deputy Associate Administrator) commented on the decision: “It would be ideal, of course, if we could build a single-stage-to-orbit shuttle, which, without shedding any boost rockets or tanks, could fly directly up to orbit and return in one piece to the take-off site for another flight. Although we may well know how to build such a vehicle some day, most studies unfortunately show that with the present state of propulsion and structural technology this objective would be just a shade too ambitious.”

Out of the 120 different concepts studied, five emerged as the most promising. ‘Concept A’ of North American as well as ‘Concept C’ of Lockheed involved a huge winged, vertically launched booster stage carrying a smaller orbital shuttle stage on its back. ‘Concept B’ of McDonnell-Douglas and ‘Concept D’ of General Dynamics both had a winged booster stage and a shuttle fitted belly-to-belly. Martin Marietta’s ‘Concept E’ involved a shuttle vehicle mated to a twin-body winged booster stage. For the orbital elements, North American, General Dynamics and Martin Marietta favored conventional, fuselage-with-wings shapes, whereas McDonnell-Douglas and Lockheed proposed lifting bodies. However, McDonnell-Douglas soon changed their shuttle design to a more conventional shape which would re-enter with folded wings. General Dynamics’ shuttle was based on a similar idea but with retractable switch-blade wings. Not having the wings extended during re-entry would save on thermal protection weight, but of course the extension system would be complicated, heavy, and involve a fair amount of risk (for example if they did not open).

For the ensuing Phase-В step of the project Lockheed teamed up with Boeing to further develop their concept, but did not win a contract. North American Rockwell and General Dynamics did, and joined forces to work on the concept of a North American shuttle stage to be launched on the back of a large winged booster designed by General Dynamics. McDonnell-Douglas and Martin Marietta, the other winning team, jointly studied a concept that was very similar but employed re-entry thermal protection based on metal alloys rather than the sihca tiles favored by North American Rockwell and General Dynamics. Both teams considered two basic orbiter designs (NASA having not expressed a preference either way): one involved Maxime Faget’s design with straight wings and lower re-entry heating but a relatively small cargo capability and a limited cross-range, and the other a delta-winged design with a greater cross-range and a larger cargo bay but higher heat loads. All Phase-B concepts were for a fully reusable launch system.

In addition to the primary Phase-В study contracts, in June 1970 NASA also let three contracts to Grumman/Boeing, Chrysler, and Lockheed to study an ‘Alternate Space Shuttle Concept’ (ASSC). This was intended as a backup plan in case the fully reusable concepts turned out to be too expensive to develop (as would soon prove to be so). The Grumman/Boeing team received the most important contract (which was later upgraded into a full Phase-В contract) for studies of a shuttle with expendable propellant tanks and of a reusable orbiter boosted by existing liquid propellant rocket engines and expendable solid rocket motors. For its ASSC contract, Lockheed further refined its Starclipper concept, which already envisaged drop tanks. The ASSC study results showed that the use of expendable tanks greatly reduced the size and weight of the orbital vehicle as well as the booster vehicle, whilst also significantly lowering the total system’s development costs.

While Phase-В was underway, NASA’s original grand plan involving large space stations, lunar bases and manned missions to Mars evaporated. This left the Space Shuttle “a project searching for a mission”, as critics in the US Congress derided it. NASA and the Air Force then began to focus on the shuttle as a stand-alone project, as a low-cost ‘space truck’ for launching, repairing and retrieving satellites, and for flying all kinds of onboard experiments. Based on what we now know to have been wildly optimistic assumptions, NASA’s plan was for a total of 445 flights during the 10 year period 1979 through 1988 (the Space Shuttle as we know it actually flew only 135 missions during its 30 year lifetime).

In May 1971 it also became clear that the government was not going to allocate sufficient funding to enable NASA to develop a fully reusable Space Shuttle. NASA and its contactors then spent the next 6 months frantically revising their concepts by incorporating expendable propellant tanks, solid propellant rocket boosters, and even modified forms of the first stage of the Saturn Y moonrocket. At the end of 1971 the manned, winged flyback booster options were discarded on the basis of the expected development cost and system complexity (both for development as well as in-service operations). By mid-1972 NASA had finally decided on the general concept for the Space Shuttle as a reusable, winged orbiter with a single expendable propellant tank and two huge solid propellant rocket boosters which would be retrieved by parachute and refurbished for reuse. Based on the expected sizes of future military spy satellites and the orbits they would require, the Orbiter had to have a huge payload bay as well as the ability to put large satellites into polar orbit from Vandenberg Air Force Base in California (from which no Shuttle ever launched, even although a nearly complete launch facility was created there). The Orbiter also required a fairly large cross-range during its descent to Earth, since its landing site in California would be rotating away from under it when returning from a reconnaissance mission involving flying a single polar orbit. Consequently the Orbiter had to be equipped with large delta-wings, and Faget’s straight-wing concept was discarded. In mid-1972 the Phase-C/D contract for the design and construction of the Orbiter was awarded to North American Rockwell. Its Rocketdyne subsidiary would supply the main engines that would burn hydrogen and oxygen, Martin Marietta would supply the external propellant tank and Thiokol would supply the sohd rocket boosters. The concept illustrations of the time show a vehicle very similar to the Space Shuttle we are familiar with. Early in 1974 NASA also decided that the Orbiter would not require jet engines, because the X-24 and other lifting bodies had proven that ‘dead-stick’ glide landings would be sufficiently safe. Discarding the (deployable) jet engines further simplified the design and resulted in considerable weight and volume savings. It did mean that Shuttle pilots had only one chance to land, but the decision was correct because not a single Orbiter ever crashed during landing.

The selected configuration had a major impact on the test flight philosophy. Up to then all crewed launch systems had been unmanned on their maiden flights. For the early Shuttle concept, when it involved a reusable winged booster stage, von Braun said in his aforementioned article that the first stage and the orbiter would each be tested separately. Although the system as a whole would be launched vertically when operational, both winged stages would initially make a series of horizontal take-offs and subsonic flights using their own jet engines. In the next step, each vehicle would make individual vertical take-offs and supersonic flights using their rocket engines. Only after these test flights had been satisfactorily concluded would the orbiter be strapped to the booster and the combination launched into space. This logic could not be applied to the Space Shuttle. The Orbiter was able to make unpowered, subsonic glide tests from the back of a Boeing 747 but the first powered flight simply had to be an all-out launch with two pilots on board because it was not designed to fly in an unmanned role. The Orbiter was not able to take off horizontally since it lacked jet engines. There was no way to flight test the large External Tank and the two Sohd Rocket Boosters separately because the Orbiter’s computers provided the commands. When astronauts John Young and Bob Crippen first flew the Space Shuttle in April 1981 NASA took an enormous risk with a new system that was so radically different from the previous manned capsules (for their later Buran shuttle the Soviets actually flew their orbiter with jet engines installed for flight tests, launched the large Energia carrier rocket separately to verify its performance, and only then launched and landed the entire Buran system unmanned).

The chosen Space Shuttle design was an awkward compromise between mission requirements, technology, costs, schedule, the need for the project to provide jobs all across the US, and the political wish for something ambitious to reassert the nation’s technological leadership. Nevertheless, NASA still believed its partial reusability and great payload capabilities would revolutionize spaceflight. Access to space would be relatively cheap, opening Earth orbit and beyond for all manner of exciting scientific, industrial and even commercial activities. In a speech to the National Space Club on 17 February 1972 NASA Deputy Administrator George Low said that now the great challenge was to develop a “productive Space Shuttle, one that performs as required, can be developed at a reasonable cost, and is economical to operate. If we meet the first two of these objectives, but not the third, we will have developed a white elephant.”

During its 30 year life the Space Shuttle performed an amazing array of missions but it never fulfilled its promise of regular, safe, economic flights into space. Instead of weekly launches NASA managed to fly an average of fewer than five missions per annum. Two of the Shuttle flights have ended in disaster; an accident rate of 1 in 68, which is rather dismal compared to the fewer than two crashes per million flights for commercial airliners in the US. Instead of costing around $40 million per flight as predicted in 1975 (equivalent to about $160 million in 2011), actual costs were closer to $500 million per launch. When also taking into account the development costs and the production costs for the five Orbiters, the actual average cost per flight was well over $1 billion!

During the 1970s NASA claimed the Orbiter’s spacious cargo bay would relax the constraints on the size and weight for its payloads, resulting in lower costs. However in reality the stringent safety constraints imposed on spacecraft and equipment meant to be transported on crewed space vehicles generally resulted in higher development and production costs than when launching on an unmanned expendable rocket.

There are several reasons why the Space Shuttle cost far more to operate and took much longer to ‘turn around’ than expected. An important reason is the maintenance of the Orbiter. For a start it had 35,000 brittle thermal protection tiles, and these had to be individually inspected after every flight and often replaced. Structural elements, instrumentation, and electrical wiring all had to be thoroughly inspected after every flight; a task that is only done periodically for normal aircraft. The Orbiter required a team of some 90 people working more than 1,030 hours in total on maintenance and refurbishment after each mission, costing about $8 million per flight in 2011 prices. Not included in this was the heavy maintenance work on the three very complicated Space Shuttle Main Engines that was done separately from the vehicle. Even though the engines only operated for 8 minutes per flight they were not nearly as reliable as airliner jet engines; they suffered more rapid wear and required a lot of checking and maintenance after each mission. In contrast, jet engines run for hundreds of hours before preventive maintenance is needed. In addition the two Solid Rocket Boosters, which landed in the ocean by parachute and were retrieved by specialized ships, had to be completely disassembled, cleaned and repaired before they could be filled with solid propellant and reassembled for reuse. Most of the things that on a conventional rocket are thrown away, with the Shuttle had to be retrieved, refurbished and than put together again. Only the large External Tank was discarded once the Shuttle had almost reached orbit and left to burn up upon falling back into the atmosphere. But that meant a new one was needed for each flight.

The idea that the Space Shuttle would launch any and all US payloads, whether from NASA, the military or commercial users, never materialized. It was simply too expensive, and it was deemed too risky to have the nation’s access to space depend on a single launch system. To stimulate the diversity of launch systems following the loss of Challenger, President Reagan even decided that commercial satellites would no longer be launched using the Shuttle. This meant a dramatic decline of the number of Shuttle launches relative to the rate advertised in the 1970s (although on the other hand that rate was unattainable). Another important reason for the reduced number of launches required was the increased lifetime of satellites, yielding lower replacement rates than were assumed during the development of the Shuttle. Another mission that was claimed for the Shuttle, retrieving satellites, was undermined by the fact that the Shuttle could not fly high enough to retrieve geostationary communications satellites (potentially the biggest market); it could only reach satellites in low orbit. In any case the retrieval of a malfunctioning satellite was usually more expensive than building a replacement. The relatively low flight rate in itself also increased the cost per flight, because the so-called fixed costs for facilities and personnel had to be shared across fewer missions. This was foreseen by several people even before the Shuttle started flying, as by, for instance, Gregg Easterbrook in the very insightful article ‘Beam Me Out Of This Death Trap, Scotty’ published by the Washington Monthly in 1979.

Roger Launius, former Chief Historian for NASA and now Senior Curator at the Smithsonian Air and Space Museum, has perfectly summarized the Shuttle program: “In 135 missions, with two catastrophic failures, the US Space Shuttle proved itself a vehicle filled with contradictions and inconsistencies. It demonstrated on many occasions remarkable capabilities, but always the cost and complexity of flying the world’s first reusable space transportation system ensured controversy and difference of opinion.”

The Soviets also investigated the development of reusable spaceplanes in the early 1960s. In 1962 the Mikoyan Design Bureau presented its ‘50-50’ concept, so-named since it would have comprised a reusable, air-breathing, hypersonic aircraft carrying a two-stage expendable rocket with a small orbital space glider. A first version of the carrier aircraft, using kerosene as fuel, would have accelerated to Mach 4 prior to releasing the rocket/spaceplane combination at an altitude of about 23 km (14 miles). A variant for the longer term would have reached Mach 6 at 30 km (19 miles) using hydrogen fuel. The orbital spaceplane was to be a lifting body with extendable wings for use during the subsonic part of the return flight. It was officially named the MiG

105 ‘Spiral’ but unofficially was the ‘Lapot’ (meaning ‘flat shoe’) for its somewhat awkward appearance. The MiG 105 would only have been able to accommodate a single cosmonaut-pilot, housed in an emergency escape capsule that could return to Earth independently even after being ejected in orbit.

The first flight of the complete 50-50 system was planned for 1977, and a group of cosmonaut-pilots started training in 1965 to fly test models and eventually the real spaceplane. But it proved difficult to maintain financial and political support because it was expensive, the technology was difficult to master and the lengthy development did not promise the quick results the Kremlin preferred. In 1973 the

cosmonaut team was disbanded and in 1976 the seriously underfunded project was finally halted. The large 50-50 carrier aircraft was never built, but a turbojet-powered prototype of the MiG 105 for subsonic tests flew eight times between 1976 and 1979, both taking off under its own power and being dropped from a Tupolev Tu-95 bomber. Today this MiG 105-11 test vehicle languishes in a muddy field at the Monino Soviet Air Force Museum outside Moscow.

Despite the 50-50 project’s demise the flight test program of the MiG 105 was continued to collect data for the new but less ambitious ‘Buran’ project. The Buran (Russian for ‘Snowstorm’) was the Soviet equivalent of the US Space Shuttle. It was developed purely to keep up with the US in technology and capability, and the Buran orbiter ended up looking remarkably similar to its American competitor. But unlike the Space Shuttle it did not use its own rocket engines for launch, it was mounted on the side of a giant Energia rocket. The Buran made only one, completely automatic, orbital flight without crew in 1988 and then the financial problems of the crumbling Soviet Union killed both the Buran and Energia projects.

The only Buran vehicle flown in space was destroyed in 2002 when the roof of its hangar collapsed due to poor maintenance, but a decrepit ground-test prototype is an attraction in a Moscow park. The atmospheric flight and landing test prototype with jet engines for a runway take-off found a more dignified home in the Technical Museum Speyer in Germany.

Being similar to the Space Shuttle, it is very unlikely that the Buran could have lowered launch costs relative to those of reliable expendable Russian launchers like Soyuz and Proton. In fact, the Russians regarded the optimistic Space Shuttle flight cost figures that NASA published during the 1970s as misinformation to disguise the Shuttle’s real purpose as an orbital bomber and “space pirate ship” for destroying or abducting Soviet satellites.

In the 1979 James Bond movie Moonraker, highjackers steal a Space Shuttle Orbiter during a transfer flight on top of its Boeing 747 carrier. They ignite its main engines and fly off, with the rocket exhaust blowing up the 747 (in reality the Orbiter was of course only transported with empty tanks for its maneuvering thrusters, and could not carry propellant for its main engines). From 1988 until 1991 the Russians briefly worked on a shuttle that would do something similar, without the destruction of its carrier. A concept called MAKS (Russian abbreviation for ‘Multipurpose Aerospace System’) involved launching a fairly small shuttle mated to a large expendable propellant tank from atop a giant, subsonic Antonov An-225 airplane (which had already been built for transporting the Buran orbiter). The standard version of the MAKS shuttle would have had a crew of two and a payload of 6,600

kg (14,500 pound) to low orbit. It was supposed to reduce the cost of transporting materials into orbit by a factor of ten. But the collapse of the Soviet Union and the ensuing poor Russian economy killed this project as well. In June 2010 Russia nevertheless announced that it was considering reviving the MAKS program.

In the early 1980s the US Air Force studied a very similar concept. It was initially called the ‘Space Sortie Vehicle’, then the ‘Air Launched Sortie Vehicle’, and finally the ‘Air Force Sortie Space System’ (AFSSS). The carrier was to be a souped-up version of the modified Boeing 747 used to transport Space Shuttle Orbiters. Several companies came up with designs based on the initial specification which involved a lifting-body mini-shuttle about 15 meters (50 feet) in length, either unmanned or with a single pilot, and powered by RL-10 rocket engines whose liquid oxygen and liquid hydrogen propellants would be in large external tanks that would be discarded when empty. Some consideration was given to wrapping these expendable tanks around the shuttle in order to create an aerodynamic assembly that would be capable of a lifting ascent, meaning generating lift to help it attain altitude after release from its carrier (in which case it would have been a real rocket plane). Rather than having its shuttle take off gently from a horizontal flying carrier (as was envisaged for MAKS) the Air Force Rocket Propulsion Laboratory had something more spectacular and effective in mind: the 747, normally not an aerobatic aircraft, would have the thrust of its jet engines augmented by the installation of afterburners: liquid hydrogen from tanks on the Boeing (also used for topping up the propellant tanks of the mini­shuttle shortly prior to launch) would be injected into the hot exhaust of the four otherwise standard turbojet engines to produce a massive increase in power of up to 400%. This would enable the giant airliner to zoom up at a 60 degree angle to reach a launch altitude of 15 to 17 km (50,000 to 55,000 feet). An alternative idea was to install a single Space Shuttle Main Engine or a cluster of RL-10 rocket engines in the tail of the 747. When standing on ‘alert status’, this rapid response system was to facilitate a flyover of any point on Earth within 75 minutes of the moment the 747 started to taxi. The shuttle was also to deliver small payloads into orbit, rendezvous with satellites or space stations, and fly “low altitude penetration of target area” missions to drop bombs before reigniting the engines to regain altitude and return to its base. As the cryogenic propellants would boil off whilst standing on alert, constant replenishment from tanks on the ground would have been required to keep the system ready for take off at a moment’s notice. This project never progressed beyond the preliminary design stage, in part because it was judged too expensive but primarily because there was no urgent need for it.

The French space agency (CNES) and the European Space Agency worked on a small, manned space shuttle named Hermes. The concept was similar to that of the X-20 Dyna-Soar, with a small space glider launched on top of a European Ariane 5 rocket. The project was approved in November 1987 but canceled in 1992 when it became apparent that neither the cost nor performance goals could be achieved. The Ariane 5 development continued as a conventional, expendable launch vehicle and is now very successful in the geostationary satellite market.

In the US, work on a successor for the Space Shuttle has not been very successful. During the 1990s NASA and prime contractor Orbital Sciences worked on the X-34, an unpiloted, experimental rocket plane powered by an inexpensive, non-reusable ‘Fastrac’ engine running on RP-1 kerosene and liquid oxygen. The X-34 was to test reusable launch vehicle technology. Like the X-15 it would have been dropped from a carrier airplane, but would have been able to reach Mach 8. But NASA canceled it in 2001 after the company refused to incorporate significant design changes without additional funding.

The most ambitious reusable launcher test project, NASA’s X-33 developed by Lockheed Martin, involved a suborbital, single-stage, unpiloted VTHL vehicle with a wedge-shaped lifting-body. It was to lift off vertically without making use of the lift generated by its shape, fly at Mach 15 and then land horizontally Uke an airplane. It was to be powered by a ‘linear aerospike’ engine that consisted of a series of small rocket motors along the outside edge of a wedge-shaped protrusion. The aerospike is essentially an inside-out bell-shaped rocket nozzle in which the ‘unwrapped’ bell (or ramp) serves as the inner wall of a virtual nozzle along which the expanding hot gas flow produces thrust. The other side of the nozzle is effectively being formed by the outside air. The advantage is that the expansion of the rocket exhaust automatically adjusts itself to the ambient pressure of the atmosphere, preventing thrust losses due to underexpansion or overexpansion. While a conventional rocket nozzle can only be optimized for a single altitude, and hence only one point in a rocket’s trajectory, an aerospike engine runs efficiently at all altitudes as well as in the vacuum of space.

Sadly the X-33 project was scrubbed in 2001 owing to major problems with the development of this aerospike engine and with the lightweight composite-material hydrogen tanks (which required complex shapes to fit the lifting-body curves). The cost of the project exceeded the $1.2 billion budget limit even before any test flights could be made. The X-33 was to have led to the development by Lockheed Martin of the operational single-stage reusable launch vehicle named ‘Venture Star’. However, it would probably have been very difficult to scale up the X-33 test vehicle without putting on too much weight, which (as explained earlier) is a frequent problem in the design of reusable single-stage launchers.

NASA’s Orbital Space Plane program to develop a crew transportation vehicle for the International Space Station was initiated in 2002. Four competing concepts from different industries emerged, three of which involved mini-shuttle designs and one a capsule spacecraft, all of which were to be launched on top of an expendable rocket. But by 2004 they had been superseded by the Orion Multi-Purpose Crew Vehicle, an Apollo-style capsule that is still under development.

In April 2010 the Air Force finally launched a small robotic demonstrator shuttle on top of an Atlas V rocket. The payload and operations of this X-37 ‘Orbital Test Vehicle’ were classified, but after 7 months in low orbit it made a gliding return. A second X-37 was launched in March 2011. The X-37 was intended to be carried into orbit inside the Space Shuttle cargo bay, but once it was realized that a Shuttle flight

would be uneconomic and moreover that the Shuttle would be retired in 2011, it was redesigned for an expendable launcher and in order to prevent its wings steering the rocket off course the mini-shuttle was covered by an aerodynamic shroud. The X-37, which was developed by Boeing, would appear to be a test vehicle for an operational military, reusable, robotic spacecraft rather than a sub-scale precursor for a crewed shuttle system.

The Space Shuttle taught us that to really lower the price of transporting people and cargo into space, we require a fully reusable launcher that is easy to maintain. Ideally, it would be a single integrated vehicle without expendable tanks or boosters that require retrieval and refurbishment. It should return to its launch site to preclude complicated and expensive transportation; if the Orbiter landed anywhere other than at Kennedy Space Center it had to be mated with a specially equipped Boeing 747, flown to Florida, then de-mated from its carrier. Instead of thousands of fragile heat resistant tiles, a limited number of readily replaceable metallic shingles ought to be employed. The propellants should be non-toxic, safe and relatively easy to handle to avoid complicated tanking and propulsion system maintenance procedures (although the various rocket planes have yielded a lot of experience in handling dangerous liquids such as hydrogen peroxide). Future reusable rocket planes may carry computers and sensors that constantly check the health of all subsystems and components in flight, both to warn the crew/flight operators of any problems during a mission and to make it easier for the turn-around team to determine when and what kind of maintenance is required. The reusable rocket engines should last longer than the Space Shuttle Main Engines, require less maintenance, and be easier to repair. The RS-25 engines of the Space Shuttle can only be operated for about 10 minutes before major maintenance, which involves time-consuming (and hence expensive) tasks and the replacement of a lot of equipment. In contrast, jet engines as used in modern airliners can operate for months of accumulated flight time with only very limited checking and maintenance. Ideally, a future space plane would have some kind of combined rocket/jet engine that can use oxygen from the atmosphere while flying at relatively low altitudes. This would mean less onboard propellant, smaller tanks, and therefore a smaller, Ughter vehicle. However, such engines tend to be complex, which potentially makes them hard to maintain.

“Make everything as simple as possible, but not simpler” – Albert Einstein

Also during the Second World War the Japanese and the Russians were actively pursuing rocket and rocket aircraft technology. In both cases this was to make up for ineffective conventional air power, but for the Japanese this necessity grew towards the end of the war whereas for the Russians the need was much more urgent during the disastrous early years of the German invasion. The accomplishments of both of these countries have been largely overshadowed by the well-known developments in Germany but are nevertheless impressive. However, as with many of the German concepts, the rush to get rocket aircraft with spectacular performance into operation led to hasty designs that lacked many of the refinements required to make the aircraft safe and of military value. Uniquely, the Japanese created a rocket vehicle that was actually intended not to be safe: a manned suicide missile. The pilots of some of the planned German rocket planes would have had little chance of surviving a mission but at least they were not specifically required to die.

Rather than losing themselves in complex technological adventures, the US and the British instead focused on the mass production and overwhelming deployment of conventional aircraft. This proved to be a devastatingly successful strategy, but it left them initially lagging considerably behind in the new military field of rocketry and rocket planes.

“Flying can never be a success until it ceases to be an adventure. ” – Sir Alan

Cobham, aviation pioneer

It does not require a leap of imagination to see that aircraft are a more economic and practical means of transportation than the ballistic rocket launchers that we are currently using. In the 1960s, orbital rocket planes with airliner-like characteristics were therefore generally expected soon to render expendable rockets obsolete, and also to lead to cost reductions of several orders of magnitude: where the flight of an expendable launcher has the cost of building a new vehicle as its price starting point, a reusable spaceplane ideally would only incur costs for propellant, maintenance and flight operations. But the availability of existing, relatively mature ballistic missile technology, the limited market for launching satellites (currently about 70 flights per annum worldwide), and the major investments and risks associated with spaceplane development have resulted in the world’s launch vehicles remaining fully expendable (with the notable exception of the partly reusable but operationally very complicated Space Shuttle, which has now been retired). As a result, for the last few decades spaceplanes have always been rather futuristic concepts, doubtless sure to supersede expendable rockets but not just yet. Launching things into space has thus remained extremely expensive and only affordable for government space agencies and several commercial applications, primarily telecommunications. As we shall see though, this is not for a lack spaceplane concepts and projects.

Just like its axis partner, Japan was seeking a ‘wonder weapon’ that could counter the overwhelming power of the AlUed forces. When Japanese military attaches first saw the Me 163 on a visit to Peenemiinde West in 1943 they were mightily impressed and recognized in the revolutionary aircraft a means of halting the expected onslaught of American bombers. The attaches had seen the devastation bombing had caused in Germany and knew that soon Japan would be facing a similar fate. The high-flying Boeing B-29 Superfortress bomber, already in production, would surely soon darken the skies over Tokyo. Still struggling to develop turbo­superchargers to enable their conventional propeller airplanes to reach the altitude at which the B-29 would cruise, Japan was desperate to find an alternative defense measure (turbo-superchargers compress the thin air at high altitude, so that sufficient oxygen gets into an aircraft’s piston engine for proper combustion).

Commander Eiichi Iwaya (who went on to play a crucial role in this story) saw a Komet demonstration at the Rechlin airfield in April 1944, then wrote in his diary: “The roar, and the blue-green flame from the Walter motor, with its immense 1,500 kg of thrust, was evidence that German technology was still ahve here, even if the combat situation was steadily getting worse.”

In early 1943 the Japanese had negotiated licences to manufacture the Me 163B and its engine, although this did not come cheap: the rights and information to build the HWK 109-509A rocket motor alone cost them 20 million Reichsmark, which is equivalent to something like $100 million today. The Japanese were allowed to study the aircraft’s production in Germany, as well as the operational procedures of the Luftwaffe. Documentation on the Komet was sent to Japan by the German submarine U-511, which left Lorient in occupied France on 10 May 1943. It was then put into service with the Japanese navy under the name RO-500. To enable Japan to build its own forms of the aircraft, Germany later agrees to supply complete blueprints for the Me 163B and the HWK 109-509A, as well as a complete Komet, two sets of sub­assemblies and components, and three complete rocket engines.

This equipment and documentation is loaded onto two Japanese submarines, one of which leaves the German harbor of Kiel on 30 March 1944 and the other leaves from Lorient just over a fortnight later. The first, RO-501, is sunk in the mid­Atlantic by the destroyer USS Francis M. Robinson. The second boat, the 1-29, reaches the harbor at Singapore. Soon thereafter, Allied intelligence intercepts a message from Berlin to Tokyo that lists all the strategic cargo carried by the 1-29. Before leaving Singapore the 1-29 commits the mistake of radioing a detailed itinerary for the final part of its journey to Japan; the message is intercepted and decoded by US Navy’s Fleet Radio Unit. The Navy sends three submarines to hunt the 1-29 and on 26 July the USS Sawfish finds the enemy boat running on the surface near the Philippines. The Navy submarine launches four torpedoes: three hit and sink the 1-29. With all the Me 163 parts and plans on the ocean floor, the Japanese would not have received any of the material sent from Germany in 1944 were it not for a Japanese naval mission member who left the 1-29 in Singapore soon after it docked. Unaware that the 1-29 is doomed by sloppy communications security, Commander Iwaya flies to Japan with a briefcase containing only twenty pages of the design manual, a photo of the Me 163B and another of its wing, a document describing the production and handling of the dangerous propellants, and data for several types of valves used on the plane. It is by no means sufficient to build a copy of the Komet and its advanced rocket engine, but this is all that reaches Tokyo.

For the Japanese aeronautical engineers the scarce information, together with what they received from the U-511 the previous year and radio telegraph communications with the air ministry in Berlin, actually turns out to be sufficient to develop their own forms of the Komet. The project is set up as a joint effort by the Imperial Japanese Army Air Service and the Navy Air Service, but they argue about how to proceed. The Army proposes to develop a new, completely Japanese rocket interceptor that can carry more propellant than the Me 163B in order to increase the duration of its powered flight. The Navy seems to better understand the urgency of Japan’s gloomy military situation, and proposes to stick as closely as possible to the already proven design of the German Me 163B. The Navy Air Service wins the dispute, and in July 1944 specifications are issued. Aircraft manufacturer Mitsubishi Jukogyo KK wins the contract to develop and produce two models of the new plane: the J8M1 ‘Syusui’ (Autumn Water) for the Navy and the almost identical Ki-200 for the Army.

However, the Army secretly decides to develop its own concept, independently of Mitsubishi, at its aero technical institute Rikugun Kokugijitsu Kenkyujo at Tachikawa (as in Germany there is considerable rivalry between the different military services, even although by now the desperate situation of the war leaves little time for such a divergence of effort). This Ki-202 is to be a better plane than the Me 163B, the J8M1 and the Ki-200, but it never leaves the drawing board. It was to have had a stretched fuselage to carry more propellant and used a KR20/Toku-Ro 3 dual­chamber rocket engine similar to the HWK 109-509C, with the large chamber and nozzle producing 20,000 Newton of thrust for take-off and climb, and the smaller one 4,000 Newton for cruise flight.

Work on the J8M1 and Ki-200 rocket plane versions quickly gets underway with Mitsubishi manufacturing the Japanese form of the HWK 109-509A engine, which is known variously as the KR10 and the Toku-Ro 2, and joining forces with Nissan and Fuji to develop the airframe. The Naval Air Technical Arsenal in Yokosuka develops the MXY8 glider ‘Akigusa’ (Autumn Grass), which will initially be used to study the handling characteristics of the Syusui and later to train its pilots. On 8 December, Lieutenant-Commander Toyohiko Inuzuka makes the first flight in an MXY8 glider after being towed into the air from Hyakurigahara airfield, and finds that it closely matches the described handling characteristics of the German Komet. Two additional gliders are made in Yokosuka, one of which is delivered to the Army for evaluation at its own aerotechnical institute.

The resulting J8M1 rocket plane looks very similar to the Komet (as intended) but it has a take-off weight some 430 kg (940 pounds) lighter due to a reduced propellant volume, less ammunition, and the deletion of the armored cockpit glass (the lack of armor protection for pilots and engines was a common feature of Japanese fighter aircraft, resulting in a weight reduction and hence increased agility at the cost of a higher vulnerability to enemy bullets). However, the weight reduction does not fully compensate for the fact that the KR10 engine produces less thrust than the original Walter engine: 14,700 instead of 17,000 Newton. The Syusui will therefore not be as fast as the Komet and will have a slower rate of climb. Nevertheless, its top speed of 900 km per hour (560 miles per hour) will still be more than sufficient to outrun any Allied propeller fighter aircraft, and its rate of climb of 48 meters per second (156 feet per second) is still phenomenal. The German Komet could achieve 960 km per hour (600 miles per hour) and had a rate of climb of 61 meters per second (199 feet per second). The distinctive power-generation propeller of the Komet is omitted from the J8M1, which instead has a longer nose section housing a battery. It is

armed with two 30-mm Type 5 cannon that can each spit out 500 rounds per minute. A J8M2 is planned that will differ only in that it sacrifices one cannon for a small increase in the propellant capacity for slightly longer endurance. The Army’s Ki-200 is very similar to the J8M1, the most important difference being that it is equipped with two 20-mm Ho-5 cannon or two 30-mm Ho-155 cannon, each of which can fire as many as 600 rounds per minute.

A production plan is put together that should lead to having at least 3,600 rocket interceptors in operation by March 1946. The first J8M1 prototype is used for load testing on the ground. The next two are for flight testing, and on 8 January 1945 one of these is towed into the air by a Nakajima B6N1 (Allied designation ‘Jill’) bomber from Hyakurigahara airfield. The aim is to test the low-speed aerodynamics, so the plane has no engine or propellant. Water is used as ballast to obtain a realistic total weight and mass balance. The test shows that the design is very good for gliding and should handle well under rocket power at high speeds.

Development of the engine is not going well. The first KR10 prototype explodes immediately upon being started, as does a modified engine known as the KR12 (the KR12 design does not offer any real advantages over the KR10 and its development is halted). Since the Japanese engineers have little experience with liquid propellant rocket engines and have only a limited amount of design and production information on the German technology, they are having difficulty designing the equivalent of the Walter engine and especially the small, high-speed turbopump. The resulting delays mean that by mid-1945 the engine is still not available and the J8M1 still cannot be flight tested under power. Time is running out because the Allied forces are virtually banging on the door of the Japanese home islands. Captain Shibata, commander of the Navy air group which is to be the first to operate the J8M1, tries to speed up the development by agreeing with the development team that the engine will be deemed ready for flight if it can operate for at least 2 minutes without failures; desperation is clearly becoming a driving factor in the plane’s development.

In the meantime, another submarine is dispatched from Germany to deliver Komet documentation and equipment to Japan. Also on board are Messerschmitt engineers Rolf von Chlingensperg and Riclef Schomerus. The U-864 leaves Bergen in Norway on 5 February 1945 but a couple of days out is obliged to return due to trouble with one of its two diesel engines. On the way back her periscope is spotted by a British submarine, HMS Venturer, which has been dispatched to intercept the U-864 and its cargo in response to the interception of German radio transmissions. On 9 February the submerged Venturer fires four torpedoes in a spread pattern at the U-864, which crash dives but suffers a hit by one torpedo and breaks in two. With it the last load of Komet equipment sent to Japan disappears into the depths.

The date for the first Syusui powered flight slips further when another engine prototype blows up. In addition, relocating the KR10 and Syusui development teams lest they be bombed by B-29s results in even more delays. Only in June 1945 does the engine meet the 2-minute thrust requirement. In fact the KR10 development team working in the Yamakita factory runs an engine for 4 minutes. The Mitsubishi J8M1 group at the Matsumoto research center runs another engine for 3 minutes. The striped pattern in the exhaust flame caused by the shock waves in the supersonic gas flow leads the engineers to dub the thrust plume the “tail of the tiger”. Unpowered glide tests of one of the Syusui prototypes with an engine installed, and tests running the engine within the plane’s fuselage, are quickly organized and successfully completed. On 7 July the first J8M1 with an engine of doubtful trustworthiness finally stands ready at Yokoku airfield for its first flight under rocket power. Following the procedure established for the Komet, Lieutenant Commander Toyohiko Inuzuka rolls 320 meters (1,050 feet) down the runway and takes to the air after only 11 seconds, successfully jettisoning the dolly. He then flies horizontally to gain speed prior to climbing at a 45 degree angle. All is well up to this point, but at an altitude of some 350 meters (1,150 feet) the engine sputters, puffs black smoke and quits. The speed of the plane carries it up a further 150 meters (500 feet) whereupon Inuzuka levels off, dumps the remaining propellant and banks to the right intending to glide back to the airfield. However, the maneuver makes the plane lose speed at an alarming rate and causes it to drift off in the direction of a small building. Inuzuka pulls the nose up in a desperate attempt to avoid it but nevertheless clips the side of the structure. The aircraft comes down in a terrible crash. Inuzuka is extracted from the wreck severely injured, and dies shortly after.

It was soon realized why the engine had cut out. For the test flight the propellant tanks had been only half-filled for safety reasons and when Inuzuka started his steep climb the liquids sloshed to the back of the tanks. But the feeds to the engine were at the front of the tanks. This deprived the engine of propellant. The reason for the feed points being at the front of the tanks was that during actual combat operations it was expected that the Syusui would climb above the enemy bombers and then attack in a powered dive. Such propellant as was left in the tanks would then slosh forward, and this had prompted the designers to put the feed lines there. The incompatibility of this system with a powered climb instead of a dive with half-filled tanks had not been noticed before the test flight. It is decided that the propellant supply system from the tanks to the KR10 must be modified, and in the meantime all powered

flight testing is stopped. While the crash investigations are underway, two new KRIOs blow up on the test stand indicating that the engine still has other issues in need of resolution.

However, less than a month after the disastrous test flight the first atomic bomb is dropped on Hiroshima. Another incinerates Nagasaki several days later. In response, Japan surrenders unconditionally.

Component production for the new airplanes had already begun in preparation for mass production of J8Mls and Ki-200s. After the three prototypes, four machines had been produced (one of them the first Ki-200). Training courses for Army and Navy pilots were also being organized using the Ku-53, an engineless glider with the same configuration and flight characteristics as the actual plane. However, even more than in Germany, the revolutionary rocket interceptor came too late to make a difference and was never used in combat.

Only two examples of the J8M1 survive today. One is on display at the Planes of Fame Museum in Chino, California. It is one of two aircraft taken to the US aboard the USS Barnes in November 1945 and which, after evaluations, were sold for scrap. One was apparently turned into pots and pans but 19-year-old Ed Maloney found the other one in a southern California storage yard. The owner of the facility thought it was some kind of boat but Maloney recognized it for what it was and bought it for the cost of its unpaid storage charges. It became the first plane in the museum that he was planning and is now the Planes of Fame Museum. Another Syusui fuselage was discovered in 1961 in a cave in the Yokosuka area south of Tokyo, badly damaged and incomplete. Until 1999 it was on display at a Japanese Air Force Base near Gifu, then it was restored and completed with replica parts by Mitsubishi, whose archives contain 80% of the original blueprints (additional information for the restoration was obtained by studying the Planes of Fame Museum example). This plane can now be viewed at the company’s Komaki Plant Museum, bearing its original bright yellow-green paint.

Towards the end of the war the Japanese Navy were also working on a completely home-grown rocket attack aircraft called the Mizuno ‘Shinryu’ (Divine Dragon). The project started as a fairly conventional-looking design for a simple kamikaze glider that could be launched from the shore using a trio of 1,300 Newton Toku-Ro Type 1 solid propellant rockets with a 10 second burn time. This plane was to crash into and thereby destroy Allied ships, or even tanks if these managed to get onto the beaches of Japan. A prototype for the glider was tested without the rocket engines, and these flights showed that the rocket propelled version could be expected to be difficult to fly. But experienced and well-trained pilots were too valuable to sacrifice in suicide attacks. A revised design was therefore proposed for a nimble attack aircraft powered by four 1,500 Newton thrust Toku-Ro Type 2 solid propellant rockets burning for 30 seconds. Armed with eight unguided air-to-ground rockets it would be able to attack ships and tanks, or even intercept B-29 bombers at a top speed of 300 km per hour (190 miles per hour) without the need for a suicidal collision. The Mizuno Shinryu was a canard design with large swept wings, small vertical stabilizer wings on the nose, and a vertical tail fin; the rocket boosters were to be fitted inside the tail part of the fuselage.

As explained earlier, the vertical stabilizers behind the wings of a conventional airplane push the tail down and compensate for the tendency of the main wings to push the nose down. An obvious disadvantage of this balancing technique is that the vertical stabilizers effectively provide negative lift, which has to be compensated by additional lift from the main wings. On a classical canard design the stabilizers are put in front of the wings, creating balance by pushing the nose up rather than the tail down; both the wings and the horizontal stabilizers provide positive lift, resulting an aerodynamically more optimal design. However if the plane pitches up, the angle of attack on the canard stabilizers increases and this gives them more lift, which in turn makes the plane’s nose rise even faster. A canard airplane can thus be rather unstable in pitch. In the hands of a skilled pilot this translates into high maneuverability but for an inexperienced pilot tends to produce a crash. There are several other pros and cons regarding canard airplanes and different effects depending upon the location of the center of gravity relative to the center of pressure (lift), but it is interesting that a number of highly maneuverable modern jet fighters have shapes remarkably similar to the Shinryu; notably the Eurofighter Typhoon, the Sukhoi Su-30 and the Dassault Rafale.

To enable it to attack B-29 bombers flying at high altitude a pressurized cockpit was proposed for the Shinryu, but a pressure suit for the pilot in combination with an unpressurised cockpit was also possible. The plane would take off with the help of a two-wheeled jettisonable dolly, and it would land using fixed skids under the wings and nose. It seems that other ways of getting the plane into the air were considered, likely involving towing or carrying by other aircraft in order to extend the range and preserve the rocket motors for the actual attack (as was proposed for several German rocket interceptors). Although some sources claim the vehicle was also designed to be used for kamikaze attacks with a warhead fitted into the nose, the complexity of the aircraft, its innovative aerodynamics for high maneuverability, and the presence of landing skids make this improbable. The plane never even reached the prototype stage before Japan surrendered, and even the earlier glider design never flew under power due to problems in developing the required rocket motors.

The only Japanese rocket airplane that actually did see action near the end of the war was the Yokosuka MXY-7 Type 11, which was more of a manned suicide anti­ship missile than a plane. It had a torpedo-shaped fuselage fitted with small, straight wooden wings and a horizontal wooden stabilizer that had a vertical fin at each end; there was also one experimental version built, the Type 21, that had thin steel wings manufactured by Nakajima instead of the standard wooden wings. The cockpit was positioned behind the wings and just behind the 1,200 kg (2,650 pound) bomb which occupied most of the fuselage. The pilot was protected by armor plating beneath as well as behind his seat because it was expected that the plane would encounter anti­aircraft fire from ships as well as from interceptor fighters. Instrumentation inside the cockpit provided the bare minimum of information required for the short flight into oblivion. Five fuses where installed to ensure the warhead would go off after impact. At least one of these was expected to be triggered by the impact shock, then detonate the bomb 1.5 seconds later so that the explosion would occur inside the target ship and cause maximum damage.

The kamikaze piloted bomb was carried partly inside the modified, doorless bomb bay of a Mitsubishi G4M (‘Betty’) bomber, and dropped within striking range of its target (interestingly, the later X-l in the US would start its mission in a very similar manner, also with the pilot entering the rocket plane inside the bomber shortly prior to the drop). The pilot would start by gliding towards his target and then ignite a trio of Type 4 Model 1 Mark 20 solid propellant rocket motors, each delivering a thrust of 2,600 Newton. He could choose to fire the motors sequentially or simultaneously depending on the range and speed required. In a sharp dive firing the rockets together in combination with gravity could smash the aircraft into a ship at about 930 km per hour (580 miles per hour). This tremendous velocity made it virtually impossible for the ship to aim its anti-aircraft guns and shoot the little plane down; something the gunners often succeeded in when attacked by much slower, conventional kamikaze planes.

The Japanese called their kamikaze weapon the ‘Ohka’ (Cherry Blossom) but the Americans referred to it as the ‘Baka’ (Idiot). The plane was conceived by Ensign Mitsuo Ohta, a transport pilot of the Japanese navy who made the first design aided by professor Taichiro Ogawa and students of the Aeronautical Research Institute at the University of Tokyo. Within weeks of contacting the university, Ohta was able to send plans to the Naval Air Technical Arsenal in Yokosuka complete with drawings, wind tunnel model test results and performance estimates. The Navy was sufficiently impressed to tell the Yokosuka engineers of its First Naval Air Technical Bureau in

August 1944 to develop the design into an operational machine. The first variant, and the only that was put into service, was the Type 11. As it would not need to take off by itself, land or fly at low speeds, its wings were kept very small to minimize drag and thereby maximize attack speed. In part because of this, the maximum range of the rocket propelled Ohka when dropped from an altitude of 6 to 8 km (20,000 to

27,0 feet) was only 36 km (23 miles). The slow and vulnerable transport bombers laden with their heavy Ohkas were therefore obliged to fly close to the targets (which often included well-defended aircraft carriers, themselves prize targets) before they could release their Ohkas. Many bombers were shot down by defending fighters long before they could get near enough to the enemy fleet to deploy their Ohka.

Solid propellant rocket motors are simple, cheap and expendable, and therefore a natural choice for a single-mission kamikaze plane. However, the disadvantage of the short range led to several Ohka proposals powered by jet engines for longer flights. None of these alternative designs could be put into operation before the war ended.

Unmanned tests of unpowered and powered prototypes were followed by the first manned Ohka flight on 31 October 1944. On that day Lieutenant Kazutoshi Nagano straps into the prototype of the Ohka K-l trainer, a version that had water tanks in the nose and tail instead of a bomb and rocket motors. For this test it has been equipped with two small solid propellant rocket boosters, one under each wing. Nagano is dropped by a Betty carrier plane at an altitude of 3.5 km (11,500 feet), pursues a stable glide for a few minutes and then fires the two motors. Immediately the machine begins to yaw, so Nagano quickly jettisons both rockets and manages to find a stable glide position once more. It is later found that the two rockets had not yielded the same amount of thrust and their positions on the wings caused the stronger rocket to attempt to turn the plane around its vertical axis (a similar problem had plagued the German Natter). Shortly prior to landing Nagano drains the water tanks in order to reduce the plane’s weight and make it possible to fly and land at a relatively low speed on skids fitted beneath the fuselage and the wings (the operational Ohkas would of course not have an undercarriage, since they were not supposed to come back). Other than during its brief moment under rocket power the airplane handled well. It is decided not to use wing-mounted rocket motors anymore, and only equip the Type 11 with three in the tail, very close to the centerline so that any difference in thrust between the boosters will have little effect on the control of the vehicle. Subsequent test flights established how the Ohka should be operated. After being released from the bomber, the Ohka pilot would enter a shallow glide at a speed between 370 and 450 km per hour (230 and 280 miles per hour). Between 8 and 12 km (5 and 7 miles) from the target, and at an altitude of about 3.5 km (11,500 feet), he would ignite all three rocket motors and accelerate to a speed of 650 km per hour (400 miles per hour), then put his machine into a 50 degree dive to scream down at 930 km per hour (580 miles per hour), at the last moment pulling up the nose in order to hit the targeted ship at the waterline.

A navy flight unit was set up to operate the Ohka. Soon nicknamed the ‘Thunder God Corps’ it drew hundreds of volunteering pilots in spite of the nonexistent career prospects. After rejecting those who were married, were only sons, had too important family responsibilities, or were simply too old, some 600 remained. They trained first with a conventional Mitsubishi A6M ‘Zero’ fighter, practicing the attack profile with the engine off. Several pilots were given some flight instruction in one of the MXY7 prototypes of the K-l two-seat trainer, but most were only able to rehearse using an Ohka while it sat on the ground.

It appears that some 751 Ohka Type 11 aircraft were built at two production sites but only a small number were deployed against the Allied fleet before the war ended, with poor results. The first time they are used is on 21 March 1945. Sixteen Betty bombers carrying Ohkas and two Bettys to provide navigation and observation are sent to attack US Navy Task Group 58, which includes the aircraft carriers Hornet, Bennington, Wasp and Belleau Wood. The bombers were to have been escorted by a force of 55 Zero fighters but owing to technical problems 25 of these either did not take off or had to turn back. Some 113 km (70 miles) from their target the planes are intercepted by 16 F6F Hellcat fighters. The Bettys immediately jettison their Ohkas, sending the pilots to watery graves without even a chance to impart damage on the enemy. All the Bettys are shot down and only 15 of the escorting Zeros make it back to base. On 1 April six Betty/Ohka combinations try again, attacking the US fleet off Okinawa. This time the bombers are able to approach close enough to their targets, and one Ohka completes a successful attack on the battleship West Virginia, causing moderate damage to one of its gun turrets. Three cargo ships are also hit by suicide aircraft but these may have been conventional kamikaze planes rather than Ohkas. The Bettys are all shot down. Eleven days later nine Bettys with Ohkas again attack the US fleet off Okinawa. One Ohka plunges onto the destroyer Mannert L. Abele, causing an explosion that rips the ship apart. The Abele becomes the first warship to be sunk by a kamikaze rocket plane, demonstrating the vulnerability of a ship to an accurately guided rocket missile flying at high speed. Another Ohka aiming for USS Jeffers is hit by anti-aircraft fire from the destroyer and blows up only 45 meters (148 feet) from the ship, imparting extensive damage. A pair of Ohkas target the destroyer Stanly and one hits it just above the waterline. However, the plane’s explosive charge punches right through the ship and explodes only after emerging from the other side of the hull, causing little damage. The other Ohka narrowly misses the ship and falls into the sea. Only one Betty survives the mission.

Further attacks on 14 April (with seven Ohkas), 16 April (six Ohkas) and 28 April (a night attack with four Ohkas) fail to produce any Ohka hits and most of the Betty carriers are shot down. On 4 May the Japanese have better luck when one of seven Ohkas sent against the US fleet near Okinawa hits the bridge of the destroyer Shea and causes extensive damage and casualties. The minesweeper Gayety is damaged by a near-miss of another Ohka. Again the price for the Japanese is high, as all but one Betty is lost (in addition to all Ohkas and their pilots). On 11 May one of the four Ohkas sent out hits the destroyer Hugh W. Hadley and causes such extensive damage and flooding that the vessel is deemed to be beyond repair. But this proves to be the final Ohka success, as the attacks on 25 May (eleven Ohkas, with most returning to base owing to bad weather) and 22 June (with six Ohkas, two of the Bettys making it home) are ineffective. Initially presuming the Ohka to be just a new type of anti-ship bomb, the Allies learn of its true nature only after capturing some of the machines on Okinawa in June 1945.

Deployed in greater numbers, the Ohka might have played a more significant role in the war but the few successes do little to stop the mighty US fleet. These attacks do show how difficult it is to stop a rocket propelled missile, and that a single hit can severely damage or even sink a large warship. The post-war development of anti-ship missiles was rapid but the kamikaze pilots were superseded by electronic guidance and the rockets were launched from fast attack jets, not lumbering bombers like the Betty whose crews had also been effectively flying suicide missions.

In an artificial cave set behind the main buildings of Kenchoji Zen Temple in the ancient Japanese capital of Kamakure there is a monument to remember the Ohka missions. A steel plaque lists all of the Ohka pilots as well as the crews of the Betty bombers who died in the first ever (and hopefully final) kamikaze attacks using a rocket plane. Another plaque in the cave tells the Ohka story, albeit from a rather nationalistic Japanese perspective. The final part of the engraved text reads: “.. .Ohka attacks together with special attacks by Zero fighters carrying bombs were made repeatedly. That heroic battle tactic made American officers and men tremble

with fear. This monument to the Jinrai warriors honors those pure and excellent young men who, without regard for their own sacrifice, courageously went to their place of death for their homeland and fellow countrymen.”

Many Ohka Type 11 have survived and are on display at museums in the US, UK and Japan. The only remaining Type 22 jet-propelled version is at the National Air and Space Museum’s Steven F. Udvar-Hazy Center, which also has a dual-cockpit trainer that seems to have been intended for preparing pilots for land-based launches, where Ohka’s would have taken off with the help of a rail launch cart equipped with two solid propellant rocket boosters.

Japan also experimented with rocket boosters to assist aircraft take off. They were applied to the Nakajima ‘Kitsuka’, a Japanese version of the Me 262 jet fighter that suffered from underperforming jet engines. It was hoped that the additional power of jettisonable rocket boosters would limit the otherwise very long take-off run of this plane. On the second test flight of the first prototype, four solid rocket boosters with a thrust of 8,000 Newton each were installed. However, they had not been set at the correct angle. Rather than adjust them, which would take too much time, the thrust of each booster was halved in the expectation that at such low thrust the misalignments would not cause a significant disturbance to the balance of the plane. On 11 August 1945, after a delay of one day owing to the high level of activity of enemy aircraft in the vicinity, pilot Lieutenant-Commander Susumu Takaoka climbs into the cockpit, has the engines started and then taxies onto the runway where he stops, extends the wing flaps for additional lift at take-off and opens the throttles of the jet engines to build up thrust prior to releasing the brakes. Four seconds into the take-off run he ignites the four boosters and promptly finds himself in serious trouble. The sudden thrust of the four downrated boosters forces the nose of the plane up and makes the tail slam down onto the runway. He pushes the stick forward but it doesn’t help. The boosters burn for 9 seconds with the plane essentially out of control. Just one second before the units bum out, the plane’s elevators suddenly take effect and slam the nose down hard. Takaoka decides to abort the flight, but his brakes have little effect. He mns off the mnway, the undercarriage collapses upon encountering a drainage ditch, and the plane slides to a standstill on its belly. The damage is severe, not only to the landing gear but more importantly to the engines slung under the wings. It is likely that the misalignment of the boosters was the cause of the problems. The Kitsuka never flew again because Japan surrendered several days after this aborted test flight and work on the project halted.

Rocket boosters were also envisaged to help the egg-shaped Kayaba ‘Katsuodori’ get up to take-off speed. This was to be a fighter plane powered by a ramjet engine. As explained earlier, a ramjet is a jet engine without a rotating compressor or turbine in which the air is instead compressed by the speed of the airplane and the shape of the air intake (in other words, the air is rammed into the engine as the plane flies through the atmosphere, increasing its pressure sufficiently for proper combustion and effective thrust). Owing to the lack of moving parts the design of a ramjet is relatively simple, is more reliable than a gas turbine engine, and ought to require less maintenance. By drawing oxygen from the air it can ran for much longer than a rocket engine on the same amount of propellant. But for the ram effect to compress the air sufficiently for the engine to start to function, the plane must already be flying at a speed of at least Mach 0.3. Hence the engine could not be used for take-off. To get the Katsuodori up to speed, four solid propellant rocket boosters were to be mounted on the side of the fuselage beneath the wing roots, in pairs, one above the other. During the horizontal take-off run on an ejectable wheeled dolly the rockets would be fired in pairs, one on each side of the plane, with each lasting 5 seconds. After the second pair burned out the plane’s speed would be sufficient for the ramjet to operate and all of the boosters would be jettisoned. But the project was shelved in 1943, probably in part due to the danger of using multiple solid propellant boosters: they cannot be stopped and if one misfires or has a lower thrust than its partners then the plane can quickly lurch out of control (recall that the German Luftwaffe used liquid propellant Walter rocket pods rather than solid propellant boosters to help their heavy bombers take off).

As in Germany, near the end of the war Japan also had a simple rocket aircraft for ramming purposes under development. Like the Zeppelin ‘Rammjager’, its pilot was to ram his rocket powered plane into an enemy bomber, then glide back for a landing (followed by another hair-raising ramming mission in the same machine until either it or he were lost). But unhke the German machine it was not armed. It would have been accelerated by four of the same solid propellant boosters as used by the Ohka. While the Ohka had only three motors and was laden with a massive warhead, four rockets with a combined thrust of 11,000 Newton would probably have been able to drive the light ramming plane to a speed of over Mach 0.9. The concept remained a paper study but if this plane had taken to the air its test pilot would likely have found himself in serious trouble since the Japanese had virtually no knowledge of transonic aerodynamics. The plane had swept wings but it is not clear whether the designers understood the benefits of such wings at transonic speeds or whether they introduced this shape merely to provide an angled edge to cut more easily through the tail of an enemy plane. It is not known whether the Japanese rammer was to be towed into the air like its German counterpart or be launched from the ground.

The US had no appreciation of how far Japanese jet and rocket plane technology had advanced until after the surrender, when they got access to the aircraft factories, many of which were hidden in tunnels in the mountains, and discovered the fleet of advanced airplanes that Japan had been busy building in preparation for the defense of their home islands. Had Japan started its advanced projects a bit earlier, and had the US been forced to invade Japan itself by conventional military means rather than forcing a surrender by dropping atomic bombs, the US ships and planes would have been met by a variety of jet and rocket planes against which they would have had little defense.

The basic, modern rocket spaceplane concept was bom in the 1930s. It involved a hypersonic rocket aircraft launched by a rail with the assistance of a rocket sled, and capable of flying almost around the globe by using a suborbital trajectory in which it repeatedly bounced off the upper layers of the atmosphere, like a flat stone skipping over the surface of a pond. This ‘rocket glider’ idea was way ahead of its time, and in fact is still ahead of our time. The ‘SilbervogeP (German for ‘Silverbird’) was the brainchild of Austrian-German aerospace engineer Eugen Sanger. He first published

M. van Pelt, Rocketing into the Future: The History and Technology of Rocket Planes, Springer Praxis Books, DOI 10.1007/978-1-4614-3200-5 8, © Springer Science+Business Media New York 2012

the idea in his 1933 book Raketenflugtechnik (Rocketflight Technology). In fact, this work was an elaborated version of his original plan for a doctoral dissertation, but his university had advised him to find a more classical topic and he subsequently got his degree for a study of aircraft wings. Rocket pioneer Hermann Oberth had shown that a rocket plane could only hope to achieve a long range by starting with a very steep ascent, leveling off at high altitude in order to use the remaining propellant to attain its maximum speed in the thin air, and then glide back down for the remainder of its flight. Sanger’s calculations led him to the same conclusions. His initial rocket plane design involved an aircraft shaped like an elongated bullet with large but thin double-wedged wings (like those of the X-2 subsequently built in the US), a small single tail fin and two small horizontal stabilizers. It bore little resemblance to the blunt-shaped biplanes of that time.

Together with Austrian-German mathematician and physicist Irene Bredt, who he would marry in 1951, Sanger further iterated the design during the 1930s and early 1940s. Initially they intended their plane to transport passengers at hypersonic speeds all over the globe but he also tried to pitch the idea as an intercontinental bomber to the Austrian military in 1933. Not surprisingly, in an age where transonic jet airliners were still science fiction the proposal was rejected, primarily because of the risk of the rocket engine exploding.

The German Luftwaffe, however, did see value in a ‘RaketenBomber’ (Rocket Bomber), as well as the basic rocket engine development and testing Sanger was already conducting at the University of Vienna. Not wanting to be outdone by the Wehrmacht (Army) and its rocket development by von Braun’s team, the Luftwaffe in 1936 invited Sanger to establish a secret rocket propulsion research institute in Trauen, Germany. It was named “aircraft test site Trauen” to hide its true nature, and Sanger was even given a fake job at the University of Braunschweig so that people wouldn’t wonder where he was working. Like Wemher von Braun, Sanger funded his work via the military as this was the only source available in Germany during the war. Under his leadership, the Trauen site quickly became an impressive laboratory with a wind tunnel, a rail launch track test rig, and a large rocket engine test stand. Sophisticated experimental rocket engines that ran on fuel oil and liquid oxygen were developed and tested, including components for a 1,000,000 Newton engine intended to propel the Silbervogel. An innovative feature of Sanger’s engine designs was the cooling of the combustion chamber by circulating propellant around it. This cooling strategy, sometimes called the ‘Sanger-Bredt design’, was actually implemented in early rocket engines such as that of the A4/V2, and in most liquid propellant rocket engines since then (including, as we have seen, those used to propel aircraft). For the engine of the Silbervogel, Sanger proposed to use a water loop to cool the massive nozzle and combustion chamber because the propellants he intended to use (fuel oil and liquid oxygen) were poor coolants. The water would be turned into superheated steam by the high temperatures in the engine and then be fed into a turbine to run the propellant pumps and the water coolant pump. After the turbine, the water would be condensed and pumped back into the cooling loop. But having three types of liquids (fuel, oxidizer and coolant) and all the associated pipes, valves and tanks made it a relatively complicated engine.

Although the Nazi government was interested in the Silbervogel as a possible ‘Amerika Bomber’, for which a number of more traditional aircraft designs were also developed, it was clear that the concept was much too advanced for the technologies available in the 1940s and that the bomber would never be ready in time to affect the war. Even Sanger himself predicted that it would take at least 20 years to make his machine operationally useful. The institute at Trauen was closed down in 1942 when the military gave priority to the VI pulsejet bomb and A4/V2 rocket developments at Peenemiinde, because these would be able to be introduced sooner and hence make a greater contribution to the war effort.

Sanger and Bredt transferred to the DFS institute in order to continue their studies and experiments on ramjet technology. But the Silbervogel never attracted sufficient support and funding, and they ended up spending most of the war developing basic rocket engine technology and a design for a ramjet fighter that never got to fly either. They nevertheless always kept thinking about their favorite concept in private and in 1944 summarized all their design and experiment work in a secret report titled ‘Uber einen Raketenantrieb fur Fernbomber’, subsequently translated and published in the US as ‘A Rocket Drive For Long Range Bombers’. The concept they finally arrived at was a 100,000 kg (220,000 pound) rocket plane that would be 28 meters long with a wingspan of 15 meters. It featured a pressurized cockpit for a single pilot near the nose, a central bomb bay, and the main rocket engine as well as two smaller auxiliary engines in the tail. The rest of the fuselage would mostly consist of two parallel rows of tanks containing a total of 90,000 kg (200,000 pounds) of liquid oxygen and fuel oil. Two short wedge-shaped wings with swept-back leading edges and a horizontal tailplane that had a small fin on each tip give the Silbervogel a conventional-looking rocket plane shape. However, the design incorporated the innovative idea of having the fuselage itself generate lift through its ‘flat iron’ shape, hence acting as a partial lifting body.

A powerful rocket sled would be used to help the Silbervogel take off from a long rail track. The sled’s rocket engines would not need to be very efficient, since they would only operate for a brief time and would not leave the track with the plane. For the sled, trading efficiency and thus propellant weight for more brute power in order to get the Silbervogel going would involve little penalty. Sanger proposed to use von Braun’s A4/V2 rocket engines. The starting speed given by the innovative rail launch system resulted in a smaller, lighter spaceplane requiring a less powerful engine and smaller wings in comparison to a similar vehicle that had to take off on its own (at higher speeds the same amount of lift can be provided with smaller wings). The rail system also meant that the Silbervogel would only need a light undercarriage for its glide landing with empty tanks, thereby further reducing its weight. Furthermore, the rail sled would make detailed knowledge of transonic flight behavior unnecessary, as it would push the plane through this mysterious region of aerodynamics whilst it was still firmly connected to the track (as mentioned above, transonic aerodynamics were not properly understood until well after the war). The rail launch system would limit the possible launch azimuths, but Sanger suggested that it could be used with either end as the starting point. As Germany’s enemies were primarily to the west (the US) and the east (the USSR), a single launch track

aligned east-west would probably have been adequate. The spaceplane would be able to alter its flight direction after leaving the track, but the larger the maneuver the more costly it would be in terms of energy and thus range. The aircraft, the rocket sled, the track and the other infrastructure on the ground would all be reusable.

The 1944 Silbervogel design was to use a 6,000,000 Newton thrust rocket sled to accelerate to a speed of 1,800 km per hour (1,100 miles per hour) on a rail track 3 km (2 mile) long. As this would occur in only 11 seconds it would expose the plane and pilot to a substantial but certainly manageable acceleration of 4.6 G. Leaving the first stage sled behind (which would have brakes to rapidly decelerate to avoid flying off the track) the Silbervogel would climb unpowered to an altitude of 1.7 km (5,600 feet) while turning into the intended direction of flight, then continue gliding up at an angle of 30 degrees. At an altitude of 3.7 km (12,000 feet), 25 seconds after take-off, the onboard 1,000,000 Newton rocket engine would fire and in about 8 minutes push the aircraft up to an altitude of 150 km (500,000 feet). Leveling off, the Silbervogel would then continue to accelerate to a speed of 22,000 km per hour (14,000 miles per hour). At the end of its powered run the aircraft would have consumed almost all of its propellant (90% of its take-off weight) and under the constant thrust of its rocket engine reached its peak acceleration of 10 G, which is about the tolerance limit for a trained pilot. In the climbing phase of the flight the G would build up gradually, as gravity would partially counteract the rocket’s thrust, but in level flight the increase from 7 G to 10 G would occur in a mere 20 seconds. Nevertheless, the pilot would sit upright with his back to the rocket engine so that his heart would not have to pump

blood into his brain against the direction of the acceleration. Knowledge gained from Luftwaffe acceleration experiments on human volunteers and drugged primates led Sanger to believe that such acceleration would not cause a well-trained pilot seated in this position to black out.

The ultimately attained speed would be some 6,000 km per hour (3,800 miles per hour) short of that required to enter orbit, so after reaching its highest altitude the Silbervogel would gradually descend into the stratosphere. However, at an altitude of 40 km (130,000 feet) the increasing air density would generate enough lift to cause the plane to “bounce” back up to about 125 km (410,000 feet) altitude. Part airplane, part satellite, the Silbervogel would repeat this profile a number of times, with each successive bounce getting shallower and covering less distance horizontally owing to the continuous loss of speed resulting from the aerodynamic drag. The aircraft would heat up each time it hit the atmosphere but have time to cool down (by radiating the heat away) during each hop back into space.

The pilot would not have much window space to admire the view because to keep the external shape smooth, and probably also the difficulty of producing windows for extreme temperatures, Sanger foresaw the pilot being provided with side view slits and “optical aids” (presumably periscopes). However, for landing, he noted, “a kind of detachable windshield can be used, since then the pressurization of the cabin and maintenance of the bullet-shape are unimportant”. Exactly what this would have involved is not entirely clear, but it seems to suggest the pilot was to open the cockpit and stick his head out when approaching the airfield; a rather awkward and archaic way to land a hypersonic spaceplane.

Sanger’s baseline hypersonic bomber, equipped with a rocket engine capable of a specific impulse of 300 seconds, would have dropped a rather small bomb of 300 kg (650 pounds) on New York, then continued its unpowered hop-fly over the continent to land in Japanese-held territory in the Pacific. The Silverbird could only lay a small explosive egg, but the psychological and hence political impact of a German bomb of any size dropped on US soil would have been substantial (as was the first US raid on Japan). With a more efficient engine and/or closer targets, the bomb load could have been increased to several metric tons. After landing as a glider (like the Space Shuttle Orbiter) the aircraft would be re-launched back to Germany, dropping another bomb on the way. From point to point, the range would be a spectacular 19,000 to

24,0 km (12,000 to 15,000 miles). Sanger proposed that it would be possible to stretch this distance even further and enable a landing back at the launch site if the efficiency of the rocket engine could be increased. One possibility to achieve this would be to add metal particles to the fuel in order to increase the exhaust temperature, improving the specific impulse to 400 seconds and so either producing higher thrust with the same propellant consumption or running the engines at the same thrust for longer without increasing the tank volume. The basic idea was sound, because metal particles were later added to solid propellants to increase the performance of boosters such as those used by the Space Shuttle. However, for liquid propellant engines it turned out to be impractical since particles can only be kept well mixed with liquid propellants if they are turned into a gel, and doing that leads to all manner of complications.

The feasibility of bouncing off the atmosphere was inadvertently demonstrated in 1962 by Neil Armstrong when flying the X-15. He came down from a high altitude with an overly steep angle of attack (i. e. with the aircraft’s nose too far up), skipped back up and as a consequence severely overshot his planned landing site at Edwards. In fact, he flew all the way to Los Angeles. However, he managed to make a gliding turn with a huge radius and thus fly back to base. Although he bounced only once, he proved the extended range of a Silbervogel-type trajectory. Crewed space capsules returning to Earth can use similar ‘skip re-entry’ trajectories, typically bouncing only once. The Apollo capsules were capable of flying such a ‘skipping’ trajectory, but it was never an operational necessity. However, the Soviet unmanned Zond prototype lunar mission capsules did demonstrate it successfully during several flights.

A postwar analysis of the aerothermodynamics of the Silbervogel discovered that Sanger and Bredt had made an error in the heat load calculations: during the first re­entry into the atmosphere the structure of the spaceplane would have become much hotter than they predicted and consequently would have needed additional protection in the form of heat shield material which would have made the vehicle much heavier than the original design, leaving little room in terms of weight for people or bombs.

After the war Sanger and Bredt were recruited by the French government to work on missiles and ramjets. In 1949 Sanger founded the Federation Astronautique, and in 1951 he was made the first president of the International Astronautical Federation that hosts the annual International Astronautical Congress. Meanwhile in the Soviet Union, Stalin had become fascinated by the Silbervogel concept, which had come to his attention through three captured copies of Sanger and Bredt’s highly secret 1944 report. Stalin saw it as a possible means of attacking the United States because the advent of nuclear weapons meant that the puny bomb load of Sanger’s design could now yield a very powerful punch. In 1947 Stalin sent his son Vasily together with aviation experts Serov and Tokayev to either win over or kidnap Sanger and Bredt and bring them to Russia to further develop their concept. However, Vasily overly enjoyed his playboy life in Paris and Tokayev defected to the British and blew the operation, so nothing came of it. By then, however, the design bureau NII-1 NKAP, established by Mstislav Keldysh in 1946 specifically to work on a Soviet version of the Silbervogel, had further elaborated on the idea presented in the captured report. By 1947 they had concluded that with the rocket engines and structures which either already existed or were likely to become available in the near future, some 95% of the initial weight of the spaceplane would have to be propellant; Sanger and Bredt had calculated ‘only’ 90%. This would leave very little weight for the structure, tanks, engines, and other essential equipment. The poor ratio between take-off weight and structural weight is a well known issue for any spaceplane concept, even today, and particularly so for a pure rocket propelled vehicle.

The Russians decided that ramjets using atmospheric oxygen instead of internal oxidizer would make the design more feasible: the weight limitation of the vehicle without propellant (i. e. the dry weight limit) would increase from 5 to 22%, while the lower maximum speed in comparison to the Silbervogel would still give the plane an intercontinental range of 12,000 km (7,500 miles). This so-called ‘Keldysh Bomber’ would have a take-off weight of about 100,000 kg (220,000 pounds). It would start with an 11 second run along a track that was 3 km (2 mile) long, pushed by a rocket sled powered by five or six liquid oxygen/kerosene RKDS-100 rocket engines with a combined thrust of 6,000,000 Newton. The bomber would climb to an altitude of 20 km (66,000 feet) and accelerate to Mach 3 using a single RKDS-100 and a pair of wingtip-mounted kerosene ramjets. The ramjets would then flame out due to a lack of oxygen and possibly be jettisoned to shed their weight. Next, the rocket engine would push the vehicle to a speed of 18,000 km per hour (11,000 miles per hour) and up into space, after which there would be a series of atmospheric skips just like the Silbervogel. It was estimated that developments in rocket and aircraft technologies would make it possible to start serious development of the design in the mid-1950s. But by then the concept of the intercontinental ballistic missile, which was easier and cheaper to develop and did not require a far-away landing site, had made the Keldysh Bomber obsolete.

Walter Domberger, the former head of A4/V2 development in Germany, tried to interest the US military in the Silbervogel concept when he joined Bell Aircraft in 1950, carefully calling it the ‘Antipodal Bomber’ rather than its wartime moniker of the ‘Amerika Bomber’ (‘antipodal’ meaning two sites exactly opposite each other on the Earth’s surface; more or less the Silbervogel’s maximum flight distance). But the sheer technical complexity of advanced materials, hypersonic aerothermodynamics and guidance accuracy, together with the doubtful military value of such an aircraft, meant that a real project never materialized. Nevertheless Dornberger’s lobbying did eventually lead to the X-15 rocket plane, the X-20 Dyna-Soar concept and ultimately the Space Shuttle. (The Shuttle is not a true rocket plane and it doesn’t use a skip re­entry trajectory but it does resemble Sanger’s design in that it has a flat base, straight fuselage sides, a rounded top, and a series of massively powerful rocket engines in the back.) The X-15 and the Shuttle incorporated several features that Sanger had not foreseen but whose inclusion would have increased both the weight and complexity of the Silbervogel. One example is a reaction control system to control the spaceplane outside the atmosphere and to properly orientate it for re-entry. Another is the need for precise guidance control sensors and electronics. Although one X-15 pilot managed to fly a manual re-entry when his guidance control system failed, for a safe re-entry both the X-15 and the Shuttle required guidance computers that were not available in the early 1950s. Such assistance would certainly have been required for the complicated bouncing trajectory of the Silbervogel.

As a passenger transporter, the original role Sanger intended for his rocket plane, the Silbervogel would have been much too complex and expensive because of its huge propellant consumption, its elaborate take-off and landing infrastructure, and its payload mass and volume allowing only a few passengers. These considerations still plague recent concepts for hypersonic airliners such as the US National Aerospace Plane (NASP) of the late 1980s. The fact that even the less complex and more economical Concorde never reached its financial break-even point makes it difficult to see how a hypersonic passenger transport vehicle could ever be a financial success.

Sanger returned to Germany in 1954 and three years later became director of the newly-created Institute for the Physics of Jet Propulsion in Stuttgart. However, when in 1961 the German government found out that Sanger was secretly making trips to Egypt, presumably to assist a group of rogue German engineers to develop missiles that could be used to attack Israel, they forced him to resign. The loss of his position, and scant prospect that his Silbervogel would be built during his lifetime, sent him into a state of depression and his health rapidly deteriorated. Sanger was unofficially rehabilitated when it was realized he had only acted as a consultant for an Egyptian meteorological sounding rocket project and had lectured at the university of Cairo. He then continued his work by assisting with a new spaceplane project at the revived Junkers company. Based on decades of research, he proposed a 200,000 kg (450,000 pound) reusable, two-stage vehicle consisting of a delta-wing carrier rocket plane and a smaller delta-wing orbital spaceplane. A steam-rocket sled was to provide a starting velocity of about 900 km per hour (560 miles per hour) at the end of a track 3 km (2 mile) long. The steam rocket would be relatively simple, using only heated water, but not very efficient in terms of performance. However, as with the original Silbervogel’s sled, that would not be particularly important for the overall spaceplane system’s performance. Its simplicity would save development effort and cost, whilst making it reusable would be relatively straightforward due to the easy – to-handle and cheap propellant (water) and the absence of extremely hot exhaust gases to eat away at the nozzle.

The orbital vehicle, called ‘HORUS’ (Hypersonic ORbital Upper Stage), would separate from the carrier at an altitude of 60 km (200,000 feet), then proceed into a 300 km (980,000 feet) orbit while the carrier plane returned to Earth. Having fulfilled its mission, HORUS would de-orbit and glide back to Earth very much like the Space Shuttle Orbiter. Both planes would be powered by similar rocket engines, three on the carrier and one on the orbital plane, each engine delivering 2,000,000

Newton of thrust at sea level and burning the powerful combination of liquid oxygen and liquid hydrogen. This is another similarity with the later Space Shuttle, whose three main engines used those propellants and each had a sea-level thrust of

1,800,0 Newton. In fact, the entire concept has similarities to some of the Space Shuttle designs of the early 1970s. Designated the Junkers RT-8, this reusable launcher was to be able to place a 3,000 kg (7,000 pound) payload into low orbit. An improved version would later use a single-stage spaceplane with an integrated rocket-ramjet engine.

In October 1963 Sanger also accepted a professorship at the Technical University of Berlin where in February 1964, aged 58, he died while giving a lecture. Shortly before his death he wrote that he believed the US and the USSR would direct their full technological capacity towards an ‘Aerospace Transporter’ similar to the RT-8 as soon as the ‘Moon Race’ ended and that “there is therefore at the moment a unique but only a short-lived opportunity for Europe, with its great intellectual and material resources, to become active in a sector of spaceflight in which the major space powers have not yet achieved an insuperable lead”. His last spaceplane design, which after his death evolved into the ‘Sanger-Г RT-8-02, would take off vertically without the need for a launch sled and rail, but it never left the drawing board. Junkers was unable to secure enough support from the government since the ambitious, expensive and economically risky project was deemed to be a step too far.

Like Max Valier, but unlike most other rocket and spaceflight enthusiasts of the time, Sanger was a real rocket plane pioneer: he fully intended his rocket engines to propel rocket aircraft rather than ballistic rockets such as the A4/V2. Sanger was certainly a genius but, Uke Wernher von Braun, his willingness to work for the Nazi military in order to move his dream machines closer to reahty, even if it meant they would be used to bomb innocent civilians, has made him a rather controversial figure (his 1944 report contains a map of New York displaying the expected efficiency of a bombing campaign by a fleet of Silbervogel planes). Irene Bredt worked for the institute in Stuttgart until 1962 and survived her husband by 19 years. In 1970 she was honored with the Hermann Oberth Gold Medal for her scientific contributions.

Sanger and Bredt’s ideas have certainly influenced rocket plane design since the end of the war: the idea for the Space Shuttle can be traced back (via Dyna-Soar and the Bell ‘Antipodal Bomber’) to their revolutionary design. In his 1963 book, which was published in 1965 in English as Space Flight; Countdown for the Future, Sanger cites all of the reasons why, in his opinion, “aerospace planes” hold the future of spaceflight instead of expendable missiles: lower costs per flight, the ability to flight- test each type of production vehicle, the possible use of airfields in densely populated countries, easy self-transportation of the vehicle from the production plant to launch site, and the ability to use them for both orbital missions and long-distance flights. These are still the principal reasons for pursuing spaceplanes although nowadays the need for (and the advantages of) such vehicles seem less obvious. Certainly nothing resembling the Silbervogel has yet been built. In the same book he writes, “military aerospace planes will be used as reconnaissance planes, fighter planes against Earth satellites and extraterrestrial space stations, satellite inspections planes etc” and also “we can possibly count space fighter planes among the most important of all space

weapons”. At that time work on the X-20 Dyna-Soar was still ongoing, but after its cancellation work on such military orbital vehicles all but ceased (with the exception of the Space Shuttle, which was partially based on military requirements). However, considering the current renewed interest by the US Air Force in hypersonic vehicles Uke the X-51 and the Falcon Hypersonic Technology Vehicle, as well as automated orbital shuttles like the X-37, Sanger may well have been right on this after all.

The development of rocket planes in Russia before the war followed a very similar path as in Germany, with spaceflight enthusiasts developing rocket motors and later incorporating them into simple gliders. However, whereas in Germany rocket plane development was not deemed to be very urgent until the situation took a turn for the worse in 1943, in Russia it was the complete opposite. When German forces invaded the Soviet Union, Russia was ill prepared and its forces were initially easily overrun. The Luftwaffe pilots were able to accumulate individual scores of hundreds of Soviet planes shot down. Russia needed a ‘wonder weapon’ quickly. The development of an operational rocket propelled interceptor became an instant priority. As the situation improved, military support for rocket plane development actually lessened in Russia, while at the same time in Germany the need for such aircraft rapidly increased.

The history of rocket planes in Russia starts with a club of rocket enthusiasts led by rocket engine developer Fridrikh Tsander called GIRD, the Russian abbreviation for ‘Group for Research of Reactive Propulsion’. Working without financial support, the members jokingly explain that the name of their organization actually means ‘Group of Engineers Working without Money’. Inspired by the Russian theoretician Konstantin Tsiolkovsky and the German rocket pioneer Hermann Oberth, Tsander is a prominent advocate of spaceflight but he doesn’t agree that other planets should be reached by expendable rockets. In an article ‘Flights to Other Planets’ published in the journal Tekhnika I zhizn in 1924 he explains that parachutes are less than optimal for landing a rocket on a planet which has an atmosphere, or indeed for returning a spacecraft to Earth, as parachutes do not offer the possibility of landing in a precise location. He continues: “For descending to a planet having sufficient atmosphere, using a rocket, as proposed by K. E. Tsiolkovsky, will also be less advantageous than using a glider or an aeroplane with an engine, because a rocket consumes much fuel during the descent, and its descent will cost, even if there is only one person in the rocket, tens of thousands of rubles, whereas descending with an aeroplane costs only several tens of rubles, and with a glider, nothing at all.” In 1933 GIRD manages to launch the first Soviet liquid propellant rocket (called the GIRD 10) to an altitude of 400 meters (1,300 feet). The rocket and its engine were mostly designed by Tsander, but sadly he died shortly before the test.

Another prominent GIRD member was Sergei Korolev, who would go on to become famous as the chief designer of the early Soviet space rockets. During the Cold War Korolev was the Russian equivalent of Wernher von Braun, and was responsible for the launches of Sputnik in 1957 and cosmonaut Gagarin in 1961 that began the space race and caused President Kennedy to direct NASA to beat the Russians to a manned landing on the Moon.

Shortly after the creation of GIRD in 1931, Korolev approaches Tsander with an idea for a rocket plane. He proposes to base this RP-1 on the existing BICh 8 tailless flying-wing glider and to power it using Tsander’s OR-2 rocket motor, which used gasoline and liquid oxygen and delivered a thrust of about 500 Newton. Later it is decided that the BICh 11 glider is better suited. In May 1932, Korolev becomes the director of GIRD and continues the design of the RP-1 and a successor called the RP-2. His work on the RP-1 and RP-2 designs evolves into the more ambitious RP – 218, a two-seat rocket plane for high-altitude research equipped with a pressurized cabin. A fixed main landing gear is planned initially, but this is soon changed to a retractable undercarriage. The RP-218 was to be taken to altitude by a carrier

airplane and released to boost itself to an altitude of 80 km (50 miles) or higher; to the edge of space, in fact. The plane is never built, partly because no rocket motor with the requisite thrust and weight is available. Interestingly, the envisaged mission scenario was very similar to that of the US X-15 rocket plane of the 1960s.

In 1935 Korolev designs the much simpler wooden SK-9 two-seater glider, which he intends to serve as a test bed for rocket motors. The RNII Rocket Scientific Research Institution, a new professional organization created by the merging of GIRD and the Gas Dynamics Laboratory in Leningrad in September 1933, sets out to transform the glider into a rocket plane by equipping it with an OR-2 engine. Being optimized to fly at relatively low speeds, modified gliders are useful for testing low-thrust engines such as this but they are not normally aerodynamically and structurally designed for the loads that come with powerful engines and high velocities. Otherwise gliders are well suited for conversion to rocket planes because they are fairly cheap and easy to modify, they do not have engines in the nose that need to be removed, they can be towed into the air by another airplane prior to starting the rocket engine, and they are able to glide to a safe landing once the propellants have been consumed. But great care has to be taken to ensure that the balance of the original design is not disturbed too much; hence most of the added weight has to be located near the original center of gravity. An added complication is that the weight of the propellant will decrease as the engine runs, whilst the fixed weight of the added structures, tanks and engine will remain unchanged. If this is not properly taken into account, an aircraft that is nicely balanced at take-off can become unstable as the flight progresses.

The rear seat of the SK-9 is replaced by a tank for 10 kg (22 pounds) of kerosene and two tanks for 20 kg (44 pounds) of fuming nitric acid. The rocket motor and its nitrogen pressurization system are installed in the aft fuselage, with the nozzle exit under the slightly modified rudder. The resulting RP-318 rocket plane has a take-off weight of 660 kg (1,460 pounds), a wingspan of 17 meters (56 feet) and a length of 7.4 meters (24 feet). The test phase begins with ground firing tests, initially with the OR – 2 controlled from the cockpit but separated from the plane by an armor plate (in case it blows up) and later with the engine installed in the aircraft. More than 30 test firings are performed. In April 1938 the plane is deemed ready for flight but then the notorious ‘purges’ of the paranoid Soviet leader, Josef Stalin, take their toll. Already, in 1937, the director and the chief engineer of the RNII institute (now called

NII-3) were executed. But a war with Germany is looming and Stalin finally realizes that shooting Russian aircraft engineers is detrimental to the quality of his air defenses. By locking them up in development center prisons instead, it will be possible to keep an eye on them while they help to design planes for the war effort. Valentin Glushko, the chief engine designer, is sent to the Butyrka prison and works in a special design bureau for “subversive elements”. When in June 1938 Korolev himself is declared an “enemy of the people” and sentenced to ten years’ hard labor in the horrible Kolyma gold mines in which temperatures regularly drop to minus 38 degrees Celsius (minus 36 degrees Fahrenheit), the development of the RP-318 halts. Although Korolev is soon transferred to a prison design bureau on the request of famous aircraft pioneer Sergei Tupolev (himself in prison) he is not permitted to work on rocketry except at night in his own time.

Only near the end of 1938 is the RP-318 project resumed at NII-3, now under the leadership of Arvid V. Pallo and without the involvement of Korolev. It is decided to repair and modify the existing prototype into the RP-318-1, involving the rebuilding of the tail section that was damaged during the ground tests, the installation of a new landing ski, and the fitting of a shock absorber to the tail skid. The most important change is the replacement of the OR-2 engine by the more powerful ORM-65 rocket engine designed by Glushko and Leonid Pushkin. But concern soon arises about this choice. The ORM-65 has been ground tested many times and flown nine times on the winged experimental RP-212 cruise missile designed by Korolev, but it is not really suitable for a reusable piloted aircraft. The engine can only be ignited on the ground and, once operating, cannot be turned off. Also the heat of the combustion degrades the engine to such an extent that it will be dangerous to attempt to use it for several flights. The design is therefore modified to make it compatible with a manned rocket plane. The resulting RDA-1-150 engine is 2 kg (4 pounds) lighter, has an improved cooling system and redesigned propellant injectors, can be ignited in flight in a low thrust regime in which only about 10% of the normal amount of propellant flows into the combustion chamber, and its operating thrust can be regulated between 700 and 1,400 Newton. The new engine is ground tested over 100 times, including 16 times while installed in the actual aircraft.

The flight test program with Vladimir Pavlovich Fedorov as pilot begins in early February 1940 at a grassy airfield in Podlipki near Moscow. It starts with unpowered glide flights using a dummy engine for mass balance and with the plane being towed to altitude by an R-5 biplane. On the first flight the propellant tanks are empty, on the second they are half filled, and on the third the full tanks are slowly drained to mimic propellant consumption by the engine. In February 1940 three low-power flights are conducted during which the engine is run in the low-thrust ignition regime. Fedorov reports that the engine can be clearly heard in his open cockpit, which means that its proper functioning can be monitored by its sound as well as by the instrumentation in the cockpit.

Finally the aircraft is ready for a full powered flight. On 28 February 1940 the RP – 318-1 is towed to an altitude of 2.8 km (1.7 miles) and released. It glides 200 meters (660 feet) down before Fedorov ignites the rocket engine. Gray smoke shows that the powder charge has fired to ignite the engine’s liquid propellant, then brown smoke shows that the engine is operating in its starting regime. As Fedorov further opens the propellant flow, a bright, almost smokeless flame nearly 1.5 meters (5 feet) long streaks from the nozzle. It pushes the RP-318-1 from 80 to 140 km per hour (50 to 90 miles per hour) in 5 seconds. Next, the plane climbs up to an altitude of 2.9 km (1.8 miles). When the engine stops after 110 seconds of continuous operation, Fedorov glides the aircraft to a safe landing. The plane makes another two successful powered flights on 10 and 19 March, after which the arriving spring melts the snow and turns the airfield into an unusable mire. In the autumn the plane is returned to NII-3 and dissembled. There are plans for further tests using another engine and a jettisonable wheeled dolly but these never take place due to other priorities within the institute. In August 1941 the German Army approaches Moscow, and as the institute prepares for evacuation to the safety of the Ural mountains the RP-318-1 is burned to prevent the Germans from finding it.

Meanwhile, in 1940 NII-3 makes a study of a plane primarily powered by wing – mounted ramjet engines and an RD-1400 rocket engine in the tail to propel the plane up to the speed required for the ramjets to start working. In the spring of 1941 a draft concept called the Tikhonravov 302 is put together under the leadership of Mikhail Tikhonravov. This is later approved by the director of the institute, Andrei Kostikov, and Tikhonravov leads a team of engineers in developing the detailed design. He also assumes responsibility for the necessary aerodynamic calculations.

Kostikov had become director of the institute after the execution of his predecessor and the imprisonment of Korolev and Glushko; all of which he seemingly engineered to advance his own career. When war breaks out with Germany and Stalin takes an interest in the new project, Kostikov decides to claim the design in the expectation that its success will raise his standing with Stalin. In November 1942 Stalin names him chief designer, and Tikhonravov’s revolutionary airplane concept becomes the Kostikov 302.

The Soviet State Defense Committee gives Kostikov only one year to get the 302 into the air. He duly promises that it will be able to fly for 20 minutes at an altitude of 8 km (26,000 feet) at a speed of 800 km per hour (500 miles per hour). A budget is allocated for the construction of two prototypes by NII-3’s OKB-55 experimental production facility headed by Matus R. Bisnovat, and a series of flight tests. The 302 is mainly wood but the elevators are made of aluminum alloy. The straight, tapered, low-slung wings have a shght dihedral for enhanced roll stability. It has a pressurized cockpit, an undercarriage with retractable main wheels and a retractable tail wheel, and hydraulic actuators to help the pilot to handle the expected large forces on the control surfaces (normally fighter planes of that time were operated by muscle power alone, which could make steering a plane at high speed with high aerodynamic forces very ‘heavy’). Because of the war, the test phase is to be minimized and the airplane turned into an operational fighter as soon as possible. Hence the 302 prototypes are equipped with armored glass in the canopy, an armor plate under the instrument panel and four ShVAK 20-mm cannon; two in the nose and two in the forward belly of the plane. In addition, the aircraft would be able to carry rockets on rails under its wings, or two 125 kg (276 pound) bombs for ground targets. The ramjets were to have been installed under the wings but development difficulties lead to the decision

to cancel them altogether and operate the plane by rocket power alone, as the 302P (‘Perekhvatchik’, Russian for Interceptor).

The lack of ramjets greatly reduces the potential range of the aircraft but it is still valuable as a short-range interceptor for fast, short-duration attacks on enemy aircraft (essentially giving it the same role as the German Me 163). The new engine chosen for the plane is the RD-2M-3V developed by Dushkin and Glushko. Like the engine developed for the German Me 263 (and for the same reason) it has two combustion chambers: a large one with 11,000 Newton of thrust for take-off and ascent, and a smaller 4,000 Newton chamber for more economical cruise flight (these numbers are the thrust given at sea level; at higher altitudes the thrust is slightly greater because atmospheric pressure hinders the outflow of the exhaust). The propellant load for this engine consists of 505 kg (1,110 pounds) of kerosene and 1,230 kg (2,710 pounds) of 96% concentrated nitric acid; a nasty and dangerous substance. These propellants are not hypergolic, so an igniter is required to initiate combustion. The pumps providing the propellant to the combustion chambers operate using 80% concentrated hydrogen peroxide and provide gas at high pressure by the process of decomposition.

In the spring of 1943 the first of the two prototypes built by OKB-55 is sent for testing in the large T-104 wind tunnel of the TsAGI institute. Glide test flights begin in August 1943 with the 302P prototype being towed by a Tupolev SB bomber to its release altitude. V. N. Yelagin is the engineer responsible for these test flights, with pilots Sergey N. Anokhin, Mark L. Gallai and Boris N. Kudrin (the nation’s oldest

active test pilot). The twelve tow flights reveal serious stability problems at speeds over 200 km per hour (120 miles per hour), which is of course a major hurdle for a plane that is one day expected to fly at transonic speeds. Modifications are made and another series of glide flights are conducted in which the 302P is towed by Tupolev SB, Tupolev Tu-2, and North American B-25 bombers (the latter one of the planes donated by the US to help the Russians in their fight against Germany). This time the 302P proves to be exceptionally stable and rather easy to fly and land while gliding, so expectations for its handling under rocket power are high. However, development of the rocket engine is lagging far behind. In early 1944 it is still not able to reach the performance required to make the 302P the effective interceptor that Kostikov promised.

With the ram engines deleted, the plane is now expected to be able to fly at 8 km (26,000 feet) altitude for only 5.3 minutes instead of the specified 20 minutes, and at 725 km per hour (450 miles per hour); some 75 km per hour (50 miles per hour) less than originally specified. If the 302P were to fly at the original altitude and speed, it would run out of propellant in just 2.5 minutes. The absolute top speed also dropped from 900 km per hour (560 miles per hour) to 800 km per hour (500 miles per hour). The machine is still expected to be able to shoot up to 9 km (30,000 feet) in only 2.8 minutes but the military value of the plane as an interceptor is now highly doubtful. Moreover, whereas at the start of the project the Soviet Union was being overrun and overflown by the Germans, by early 1944 the need for an advanced interceptor plane is less urgent. In March 1944 it is decided to cancel the entire program, although one powered flight of the first 302P prototype remains in the planning. In the winter of 1944 it is fitted with skids and makes its first and final flight powered by an RD-2M3 rocket engine. Details are scarce but eyewitnesses say the flight was a success, even though one of the undercarriage ski legs failed at touchdown and caused the plane to slew into a snowdrift. However, the failure of the 302P as an effective weapon has dire consequences for Kostikov. Despite having the ‘Hero of Socialist Labor’ medal and the Stalin Prize, he is sent to prison on 15 March 1944 for obstructing the war effort and is not released until 1945.

During 1942 Aleksandr Yakovlev, the famous designer of Russian fighter aircraft, worked on the design of a concept very similar to the 302. It was to be based on his Yak-7, but instead of a piston engine and propeller it was to be driven by two ramjets mounted under the wings and a Dushkin D-l-A liquid propellant rocket motor in the rear fuselage. The result would be the Yak-7R (the ‘R’ standing for ‘Reaktivnyy’, meaning ‘Reaction-propelled’). But the project never left the drawing board owing to the lack of reliable ramjets.

The most famous Soviet rocket plane of the Second World War is the Bereznyak – Isaev BI. This story begins in the spring of 1940, when the Zhukovsky Institute in Moscow (TsAGI) hosted a conference on ramjet and rocket propulsion. It is probable that the meeting was inspired, at least partially, by the advanced rocket and aircraft developments in Germany, which they knew of because Soviet intelligence had been able to recruit Willy Lehmann, a German Gestapo officer who kept them informed. Among the attendees were Viktor Fedorovich Bolkhovitinov, head of design bureau OKB-293, and Aleksandr Ya. Bereznyak and A. M. Isaev, two of his top engineers. Both Bereznyak and Isaev were very excited by the idea of rocket propelled aircraft and convinced Bolkhovitinov to let them start to design one. In the autumn of 1940 they showed fellow engineer Boris Chertok a preliminary design of what they called ‘Project G’. It was a concept for a compact plane built of wood and duralumin (an aluminum alloy) with a take-off weight of 1,500 kg (3,300 pounds). To serve as an operational interceptor it was to have four machine guns; two 12.7­mm and two 7.6-mm caliber. The engineers intended to power their plane with a new

14,0 Newton rocket engine burning low-grade kerosene and red fuming nitric acid that was under development at NII-3 by a team led by Leonid Dushkin (who had also designed the RDA-1-150 that powered the RP-318-1). Since the thrust of the engine was close to the maximum weight of the plane, which would decrease as it burned propellant, it would be able to climb almost vertically once airborne. The top speed was estimated at 850 to 900 km per hour (530 to 560 miles per hour). According to the designers the most important selling points were the incredibly fast climbing rate (enabling it to reach enemy planes quickly and intercept them by surprise), its high speed (making it virtually invulnerable to enemy fighters), and the inherent simplicity of the rocket in terms of manufacturing and maintenance when compared to high-performance piston engines.

Bereznyak, Isaev and Chertok visited NII-3 in March 1941 to check on the status of the rocket engine, called the D-l-A-1100. This was state-of-the-art at the time. It weighed 48 kg (106 pounds) and consisted of several large forged-steel sections (the conical head with 60 propellant injectors, the cylindrical combustion chamber and the nozzle) joined using bolts and copper gaskets. Cooling was provided by pumping the kerosene fuel through the double-walled combustion chamber and the nitric acid oxidizer through the double-walled nozzle. The engine was ignited using a glowing plug of nichrome; later replaced by silicon carbide. But this marvelous technology was not working yet, mostly due to problems with Dushkin’s innovative turbopump driven by hot gas and steam produced by a small combustion chamber that was fed a mixture of water and the same propellant as the main rocket combustion chamber; an efficient but complicated affair. Furthermore, the engine was not going to deliver the specified 14,000 Newton of thrust: the prediction was that it would deliver no more than 11,000 Newton. On 21 June Isaev proposed running the engine’s turbopump on compressed air instead; it would result in a heavier rocket engine but would be much simpler.

The very next day Germany invaded the Soviet Union and the need for the rocket propelled interceptor instantly became very urgent. Bereznyak and Isaev set to work on a new, more detailed design. They finished it in only three weeks and on 9 July, together with Bolkhovitinov, met with the head of NII-3, the earlier mentioned Andrei Kostikov. Although Dushkin was not happy with the idea of altering his fuel pump, Kostikov agreed that the urgency of the situation meant that using compressed air made sense. A letter was sent to the Kremlin, and it was even shown to Stalin personally. The Project G team went to Moscow to report on their design and were ordered to build the plane in only 35 days. The engineers were given leave to visit their families, then literally lived in the factory to meet the extremely demanding deadline. The same order tasked NII-3 to finish the development of the D-1-А-1100 engine as soon as possible, and make it capable of multiple restarts in flight as well as thrust variation in the range 4,000 to 11,000 Newton.

The new design was called the BI for ‘Blizhnii Istrebitel’ (Close-range Fighter) and also the first letters of the two inventors Bereznyak and Isaev, although whether this was deliberate is unclear. It was now a sleek low-wing machine with a length of only 6.4 meters (21 ft) and a wingspan of 6.5 meters (21 ft). The take-off weight was 1,650 kg (3,640 pounds), of which 710 kg (1,570 pounds) was propellant. This made the BI a very diminutive fighter aircraft; smaller and lighter than the Me 163B. For comparison the conventional German Messerschmitt Bf 109G fighter had a length of

9.0 meters (29 ft), a wingspan of 9.9 meters (33 ft) and a maximum take-off weight of 3,400 kg (7,500 pounds), and was still regarded as being a relatively small fighter. The BI was kept as simple as possible so that it could be produced in short order and in sufficient numbers to overcome the German invasion of Soviet airspace. The four machine guns planned earher were replaced by two more powerful 20-mm ShVAK cannon. The BI would have a wooden frame and a 2 mm (0.08 inch) plywood skin covered by a bonded fabric, and it would be easy to mass produce. The wings were to be relatively short to limit drag whilst still providing sufficient lift at the planned high flight speeds (lift is a function of both the area of the wings and the flight speed, so at higher speeds smaller wings are sufficient). However they were not particularly well designed for transonic flight phenomena (something that will result in a serious accident, as we shall see). The ailerons, elevators and rudder were covered by fabric but the flaps were duralumin. Ten tanks with compressed air (held at a pressure of 60 atmospheres), five in the forward section and five in the aft section, were required for the rocket engine’s turbopump, to retract and deploy the landing gear, and to power the cannon. The forward section also housed two kerosene fuel tanks while the aft section had three tanks of nitric acid oxidizer. The air tanks were made from a high – strength steel (Chromansil) that was great for making light pressure vessels but not very resistant to corrosion. Their proximity to the extremely corrosive nitric acid was thus rather hazardous and required the acid tanks to be replaced periodically in order to ensure that no leaks could develop.

Working around the clock (with local furniture makers supplying the wood-and – fabric airframe) the team delivers the first prototype on 1 September 1941. A second prototype is also being assembled. However, Dushkin’s engine is still not available. The first prototype, BI-1, is towed into the air by a Pe-2 bomber on 10 September with test pilot Boris Kudrin at the controls. Following release, he glides back to the airfield and makes a successful landing. Another fourteen unpowered flights follow and establish that the plane behaves well at low speeds. Interestingly, rival aircraft designer A. S. Yakovlev had the prototype towed to the TsAGI T-104 wind tunnel for testing. This alarmed the BI team because Bolkhovitinov had a rather rocky history with Yakovlev, but Yakovlev himself, and his aircraft designer, Ilya Florov, studied the results and gave the team good suggestions for improvements. In this way a yaw instability was corrected by enlarging of the rudder and adding two circular vertical plates at the tips of the horizontal stabilizer.

In addition to the problems with the engine, the BI project was delayed by the evacuation of both OKB-293 and NII-3 in October 1941 (in preparing for which, as mentioned above, the RP-318-1 rocket plane was burned). Most of Moscow’s vital war industries were moved deep into the Ural mountains to ensure they would not be overrun by the rapidly advancing Germans. The BI team was stationed in Bilimbay but Dushkin’s team ended up 60 km (37 miles) away in Sverdlovsk. Near their new accommodation the team built a test stand for their aircraft on the shore of the frozen Lake Bilimbay. It comprised a cradle that could hold the plane during engine tests, as well as measure the thrust. But there was still no engine to install. Dushkin was now increasingly absorbed by other projects (including NII-3’s own Kostikov 302 rocket plane) but he assigned his engineer Arvid Pallo to oversee the installation and testing of the rocket engine. When the static test campaign finally begins in early 1942 it becomes immediately clear that the nasty nitric acid is trouble: it corrodes parts of the airplane as well team members, causing skin burns and respiratory irritation. Tanks of sodium carbonate solution have to be kept handy to neutralize the all-too-frequent acid spills. For these tests the new test pilot Grigory Yakovlevich Bakhchivandzhi (Kudrin was ill) operates the engine from the cockpit: a method fraught with risk, as we have seen with the He 112 which almost killed Erich Warsitz during a ground test. Indeed, on 20 February the BI-l’s engine explodes, blasting the nozzle section into the lake. The forward assembly of the engine smashes through the airframe and strikes the rear of Bakhchivandzhi’s seat, knocking him against the instrument panel. Fortunately his injuries are minor. Nitric acid spraying from a broken propellant line drenches Pallo. Luckily his eyes are saved by his protective glasses and the rest of his face is partly spared by alert mechanics who dunk him head-first into a tank of soda solution. His scars serve as a grim reminder of the dangers of rocket testing. A study of the engine debris reveals that the combustion chamber had succumbed to corrosion fatigue. In pushing on with the testing phase despite a shortage of engines, the one D-l-A-1100 available had been operated too many times and for too long. After the test bench is rebuilt and the engine’s propellant supply system improved, static firing tests resume, with the undeterred Bakhchivandzhi performing three of them. A 5.5 mm (0.22 inch) steel plate is added to the rear of the pilot’s seat as protection.

By April 1942 the BI-1 is deemed ready for flight testing at the nearby Koltsovo airfield (now the main airport of the city of Sverdlovsk). Interestingly, in spite of the obvious danger, the nitric acid for the engine is actually transported to the airfield in glass bottles and there poured into the containers from which it will subsequently be fed into the plane’s tanks. All of this is done without any protective clothing.

On 2 May Bakhchivandzhi takes the controls of the BI for a short, low-thrust hop one meter above the ground. Then on 15 May he prepares for the first real test flight. Like the Me 163, the BI could explode if it were to make a hard landing before all the propellant was consumed, so it is loaded with only 240 kg (530 pounds) of nitric acid and 60 kg (130 pounds) of kerosene. He arrives wearing a new leather coat and shiny boots but when he climbs into the cockpit he is wearing his old flying gear: he explains that if he doesn’t survive the flight the new coat and boots will be useful for his wife… she could make some money by selhng them! Taking off under rocket power, he leaps into the air and quickly reaches an altitude of 840 meters (2,800 feet) and a speed of 360 km per hour (220 miles per hour) with the thrust limited to 8,000 Newton. Another safety measure, a fairly standard one for the early flights of new airplane prototypes, is that the undercarriage is kept down. After one minute, an indicator lamp reports the rocket is overheating, so he shuts the engine off. Gliding in to land, the plane descends too rapidly owing to insufficient forward speed and the resulting lack of lift. The touchdown is hard and breaks the undercarriage but the plane is not significantly damaged. Bakhchivandzhi lives to wear his new coat and boots another day.

Compared to today’s test flying, taking up a plane for the first time was in those days a truly scary business, especially if it was powered by a rocket engine. Modern airplane prototypes have already been exhaustively tested by sophisticated computer simulations long before metal is cut. The designs are based on an enormous database on subsonic, transonic and supersonic aerodynamics, control theory, materials and so on. Engines are tested hundreds of times before being deemed sufficiently reliable to be fitted into an airplane. All of this ensures that the question to be answered by the first flight is not whether it will fly, but rather how well it matches the performance predictions.

In contrast, pilots taking up revolutionary barely tested machines like the Me 163, Syusui and BI were really pushing very experimental technology into the unknown. Rather than wondering how the planes would fly, their minds were probably more occupied with the question how these new beasts were going to try to kill them. And unlike modem pilots, these pioneers did not have teams of engineers monitoring the flight on the ground, ready to help in case of trouble; once in the air, they were truly on their own. Last but not least, they had no ejection seat to instantly boost them out of a hairy situation.

The BI’s first flight lasted only 3 minutes and 9 seconds but was judged a success, with Bakhchivandzhi reporting, “the aircraft performed stable decelerations, gliding and handhng like any ordinary aircraft”. The State commission in charge of assessing the BI project delightedly noted: “The take-off and flight of the BI-1 aircraft with a rocket motor used for the first time as the aircraft’s main engine has proved the practical feasibility of flight based on a new principle; this opens up a new direction in the development of aviation.” This flight is sometimes hailed as that of the world’s first operational rocket fighter plane, but this is somewhat of a stretch. Even though the BI was designed as an operational weapon, it was still very much experimental. It is certainly true that it flew before the first Me 163B in Germany, but the DFS 194 and Me 163A predecessors of that machine had taken to the air long before the first BI flight.

Encouraged, Stalin authorizes the production of a batch of 30 BI interceptors for operational military service. These are enhanced with racks for small bombs that can be dropped onto enemy bomber formations by flying above them, causing damage by a combination of shock waves and shrapnel. The decision to declare the BI ready for military service after only a single low-speed flight soon proves to be premature.

In July, Pallo is recalled to NII-3 by Dushkin to help him with the institute’s own Kostikov 302 rocket plane. Isaev takes over management of the BI’s rocket engine in OKB-293. To help get started, he goes to learn the tricks of the trade from Valentin Glushko in the Butyrka prison design bureau. Glushko shows Isaev how to improve the engine, and Isaev starts to work on what will become the RD-1 rocket engine that will later be incorporated in the BI aircraft.

After its first and only flight, the BI-1 is deemed too damaged by nitric acid spills for safe flight and it is retired. Testing continues using the second prototype. On 10 January 1943 Bakhchivandzhi flies the BI-2 for the first time. He still limits the D-l – A-l 100’s thrust to 8,000 Newton and the speed to 400 km per hour (250 miles per hour) and hence achieves an altitude of only 1,100 meters (3,600 feet). This time the undercarriage, with skids instead of wheels for taking off from the snowy airfield, is retracted, resulting in a smoother flight with aerodynamics more representative of a BI interceptor in operational use.

A third flight (the second with the BI-2) is made two days later by another pilot, Konstantin Gruzdev. (Bakhchivandzhi was at that time visiting NII-3 to check upon progress with the Kostikov 302; there was clearly a great deal of interaction between the rocket plane teams of NII-3 and OKB-293.) This time the propellant flow is fully opened, allowing the engine to provide its full thrust of 11,000 Newton. At the peak altitude of 2,190 meters (7,190 feet) Gruzdev achieves a speed of 675 km per hour (420 miles per hour). When he extends the undercarriage one of the skids breaks off but he manages to land safely. Asked about the flight, Gruzdev comments, “It’s fast, it’s scary, and it really pushes you in the back. You feel like a devil riding a broom.” Henceforth the ‘devil’s broomstick’ nickname is used by everyone who works on the BI project. Film of this flight has survived, showing the BI accelerating quickly over the frozen lake, taking off and shooting up. The less than perfect landing was also captured, with the plane toppling forward because of the broken skid and performing a ground loop as it skidded across the ice. If such a thing had happened on a grassy airfield the plane would probably have burrowed its nose in the ground, with a much more severe outcome.

On his return Bakhchivandzhi takes over from Gruzdev and flies the refurbished ski-equipped BI-1 prototype on 11 and 14 March 1943, and on the 21st he takes off in the third BI prototype (also on skids) and climbs at a maximum rate of 83 meters (272 feet) per second; this is about half the rate of an Me 163B but still at least five times better than contemporary Russian piston-engine propeller fighters. On the 27th Bakhchivandzhi makes another low-altitude test flight. After 78 seconds, as he opens the throttle to push the plane beyond its speed record, the BI-3 suddenly goes into a 50 degree dive and smashes into a frozen lake instantly killing the pilot. The BI team has discovered the infamous transonic ‘Mach tuck’ phenomenon the hard way. This is confirmed by tests in TsAGI’s new T-106 high-subsonic wind tunnel. The BI – 3’s onboard recording instruments were too badly mangled by the crash to give accurate data on the final speed, but estimates range from 800 up to an astonishing 990 km per hour (500 to 620 miles per hour). This disaster prompts the Air Force to cancel the pre-production order. For his achievements and ultimate sacrifice Bakhchivandzhi is posthumously awarded the ‘Order of Lenin’. (In 1973 he gained the more prestigious ‘Hero of the Soviet Union’.)

In May 1943, with OKB-293 relocated to Moscow following the German retreat, Bolkhovitinov writes a detailed report on the experiences with the BI prototypes. He emphasizes the need to study the shock effects that had caused the BI-3 to crash, and in order to investigate transonic and supersonic flight dynamics he recommends the development of a rocket plane capable of 2,000 km per hour (1,200 miles per hour).

No BI flights are made for over a year, probably in part because the urgent need for an operational rocket interceptor has lessened considerably, but also because time is required to build new airplanes. In 1944 five more prototypes are readied. BI – 6 is given a pair of ramjet engines instead of a rocket engine. It is towed into the air on three occasions but the test pilot never manages to get the engines to work properly. The other prototypes are to be fitted with the new RD-1 rocket engine designed by Isaev, the first example of which is completed and tested in October 1944 (it should not be confused with the smaller RD-1 engine of Dushkin and Glushko).

The general layout of the engine is similar to that of the D – 1-А-1100 and also has a maximum thrust of 11,000 Newton, but Isaev has introduced numerous improve­ments, including a more reliable electric-arc igniter instead of the glow plug, and new injectors designed to improve the fuel and oxidizer mix in the combustion chamber. The BI-7 is fitted with the Isaev RD-1 and flown by test pilot Boris Kudrin on 24 January and 9 March 1945. The maximum speed attained is 587 km per hour (365 miles per hour), which is well short of the dangerous transonic flight regime. These flights reveal a problem of excessive vibration in the tail. Gliding tests using the BI-5 and BI-6 are made to investigate the problem but the pilots are unable to recreate the vibration. However, by this point the war is nearly over and there is no operational requirement for the BI interceptor, so work is halted. The ‘devil’s broomstick’ is never flown in combat but its developers have gained valuable experience that will be put to good use after the war in developing new rocket propelled aircraft.

No examples of the BI survive but a reasonably accurate replica can be seen in the Russian Federation Air Force Museum in Monino. At the airport of Sverdlovsk, a monument of a BI replica shooting into the sky commemorates the rocket aircraft’s first flight from that location.

Another rocket plane that however never progressed as far as the BI was the ‘Malyutka’ (Little One), the final aircraft designed by famous aviation pioneer N. N. Polikarpov. The construction of a prototype started in early 1944 and was nearly complete by the middle of the year. However, all work was suddenly stopped when Polikarpov died of a heart attack on 30 July of that year, and his facilities were absorbed into the rival Lavochkin design bureau. Work on the project was never resumed.

The Malyutka was initially planned to use a D-l-A-1100, the same rocket engine as powered the BI, but it was later decided to use a dual-chamber RD-2M-3V, which was the same engine as intended for the Kostikov 302P. The combined thrust of the two chambers was expected to be sufficient for a top speed of 845 km per hour (525 miles per hour). As the propellants were consumed, the changing center of gravity of the aircraft would cause stability problems. The solution was to equip the plane with a tank from which water could be discharged in order to compensate for the changing weight balance; simple but not very elegant. The fuselage would be made of wood, but unlike any previous Polikarpov fighter the wings and tail section would be lightweight aluminum alloy. The aerodynamic control surfaces would be operated by a pneumatic system, the cockpit would be pressurized for high-altitude flight, and the armament would comprise two powerful VYa-23 23-mm cannon. In contrast to the conventional undercarriage of the 302P and the BI, the Malyutka would employ an undercarriage and a retractable nose-wheel instead of a tail wheel. A plane with a tail wheel (a so-called ‘tail-dragger’) has its nose angled up whilst taxing, which makes such an undercarriage a good choice for a machine driven by a propeller that has to clear the ground. However, a jet or rocket aircraft has no need for a large ground clearance of its nose and so can be equipped with a nose wheel in order to align the plane more horizontally on the runway. This gives the pilot a much better view of where he is going during taxiing and the take-off run. Furthermore, with the plane in a horizontal position there is less danger of jet or rocket engine exhaust melting the runway. While most propeller fighter aircraft of the two world wars had tail wheels, nearly all jet fighters employ so-called tricycle undercarriages, with wheels under the wings and the nose.

The idea of adding rocket engines onto existing piston-engined airplanes (like the Germans with the Heinkel 112) was also explored as a stop-gap while waiting for the rocket and jet airplanes. The 3,000 Newton thrust Dushkin and Glushko RD-1 engine was fitted to various types of aircraft to boost their performance. On 1 October 1943 tests began with the engine in the aft fuselage of a Petlyakov Pe-2 dive bomber, with the turbopump driven by one of the two standard piston propeller engines. The tests with the Pe-2RD prototype revealed problems with the RD-l’s electrical ignition, so it was replaced by a chemical ignition system. Both the RD-1 and the RD-lKhZ (the improved engine) were also flown on two Lavochkin La-7 fighters (the La-7R1 and La-7R2), an older La-7 prototype airframe (the La-120, converted into the La-120R), a Sukhoi Su-7 high-altitude interceptor (the original Su-7, not the jet fighter that was introduced in the 1950s with the same designation) and a Yakovlev Yak-3.

These tests proved the concept. For instance, on 11 May 1945 the rocket-equipped Yak-3, the Yak-3RD, reached a speed of 782 km per hour (486 miles per hour) at an altitude of 7.8 km (25,600 feet); some 130 km per hour (80 miles per hour) faster than the top speed of a conventional Yak-3. Indeed, it seems that a La-7R with an operating rocket motor successfully participated in the Moscow air displays of 1946 and 1947. However, on several flights the RD-1 exploded as kerosene fuel and nitric acid oxidizer came into contact outside the combustion chamber owing to leaks. The brave test pilots were usually able to land their damaged planes. One pilot of the sole rocket propelled Su-7 prototype was not so lucky, because while preparing the plane

for the first post-war air display over Moscow in 1945 the rocket motor exploded, destroying the aircraft and kilhng him. On 16 August 1945 test pilot V. L. Rastorguev died when his experimental Yak-3RD crashed for unknown reasons.

It became clear that apart from reliable and safe rocket engines, Russia also lacked vital knowledge on the dynamics of transonic flight. By 1935 Aleksandr Moskalyov had already drafted a concept for a rocket propelled aircraft that he thought should be able to exceed the speed of sound. The planform for this plane was based on that of his SAM-9 ‘Strela’ (Arrow), a propeller aircraft that had a revolutionary ogival delta wing (also known as a Gothic delta because its shape resembles the arches in Gothic cathedrals). Moskalyov expected this type of wing to be well suited for transonic and supersonic flight, and this was later confirmed by the supersonic, ogival delta-winged British-French Concorde and Russian Tupolev 144 (‘Konkordski’) airliners. Piston engines and propellers were not going to show the full potential of his wing, but with a rocket engine he expected to be able to reach transonic speeds and beyond.

With Dushkin’s help for the propulsion part, in 1944 Moskalyov came up with the design for the SAM-29, also known as the RM-1 (for ‘Raketnyi Moskalyov’, Russian for Moskalyov Rocket). Like the Strela, it had an ogival delta wing and big vertical stabilizer, but no horizontal tail. The planned engine was Dushkin’s RD-2M – 3V. To comply with the military’s rather impractical demand that any new rocket plane must be armed to serve as an operational fighter, the experimental RM-1 would have two cannon in the nose. Unfortunately, at the end of the war the project

was deemed too futuristic and in January 1946 Moskalyov’s design bureau was closed. Had those in power understood the RM-l’s potential and continued their support, then either it or a close descendant might well have become the first aircraft ever to fly faster than the speed of sound.

More or less in parallel with the RM-1, the development of another dedicated research rocket aircraft concept started in 1943. Designer Ilya Florentyevich Florov led the project for the Russian Air Force, and his Florov 4302/4303 was a relatively small rocket plane made entirely of light alloy. Its exterior had a very smooth finish to minimize aerodynamic drag, but unlike the Me 163 and various other high-speed German designs it had straight wings rather than swept back wings or delta wings. It is unlikely that the benefits of swept wings for transonic flight were fully understood in Russia at that time. (Nor indeed, as we shall see in the description of the post-war X-l, was the concept of the swept wing understood in the United States). The fully horizontal wings of Florov’s design, which were set high on the fuselage, had down­ward angled ‘flippers’ at the tips. These effectively produced a negative dihedral in order to avoid ‘Dutch roll’, a stability problem common to high-winged aircraft that imparts an out-of-phase combination of ‘tail-wagging’ and rocking from side to side. (The German He 162 jet plane that flew near the end of the war also had a high wing and similar drooping wingtips, which the Germans called ‘Lippisch Ears’.) The pilot was housed in a small pressurized cockpit. Three aircraft were built. The first had a fixed undercarriage with a tail wheel (using parts from a Lavochkin La-5FN fighter plane) and was intended for low-speed gliding flights only. The other two aircraft were for powered flight and (like the German Me 163B) were to take off employing an ejectable tricycle dolly, then land on a skid and a tail wheel. Aircraft 2 would be a

Florov 4302 with a nitric acid/kerosene RD-1 rocket engine designed by Isaev with a maximum thrust of 11,000 Newton at sea level. Plane number 3 would be finished as a Florov 4303 with the RD-2M-3V two-chamber engine (the same engine that was planned for the Kostikov 302P and the Polikarpov Malyutka) delivering a combined maximum thrust of 15,000 Newton at sea level.

However, the flight test phase only begins in 1946, well after the end of the war. Pilots A. F. Pakhomov and I. F. Yakubov are appointed and that year make 46 towed glide flights with aircraft number 1. After some taxi tests and a short hop, Number 2 is flown for the first time under rocket power in August 1947, with Pakhomov at the controls. He is towed to an altitude of 5.0 km (16,400 feet) by a Tu-2 bomber. After release, he ignites the rocket engine and quickly accelerates to a speed of 826 km per hour (513 miles per hour), which is rather daring in a new experimental airplane that has not previously been tested under power at lower thrusts and speeds. Afterwards Pakhomov reports that the plane behaved well in all respects, and there were no vibrations. Several more flights with the 4302 then follow, and on one occasion a propellant feed line ruptures and noxious acid vapors slightly intoxicate the pilot. But by late summer 1947 the concept of the Florov 4302/4303 was obsolete thanks to the new information on high-speed flight and aerodynamics obtained from the defeated Germans. Moreover, jet fighters were now reaching similar speeds as those for which the 4302/4303 were designed. It was therefore decided that sufficient data had been gathered from the testing and that it would be better to concentrate effort and funding on the more advanced MiG 1-270 rocket plane (described in the next chapter). When the 4302/4303 program was halted, aircraft number 3 was still awaiting its engine.

While on the subject of future spaceplanes let us have a look at how these were (and still are) depicted in fiction. The existence of spaceplanes as an efficient means of transportation between Earth and space is generally taken for granted in science fiction, much like airliners are used in the real world. Apart from ideal aircraft-like operations, one thing that most of the spaceplanes in science fiction books, movies and television series appear to have in common is an amazingly efficient propulsion system because most of the volume is available for passengers and cargo rather than being taken up by bulky propellant tanks.

Take for instance the Orion III ‘Pan Am Space Clipper’ of the famous movie 2001, A Space Odyssey of 1968. We are shown a spaceplane that operates much like an airliner, even with stewardesses. No take-off is shown in the movie but it appears that the Orion is a single stage vehicle with double-delta wings (similar to those of the Space Shuttle, which had not yet been designed when the movie was produced). Windows cover only a short stretch of the middle of the fuselage, which makes sense for a spaceplane requiring large volumes of propellant. Still, as a relatively small single-stage-to-orbit spaceplane (judging from the size of the windows) 200Гs Orion must have fantastically efficient engines; jet engines, if the series of holes that can be seen on the leading edges of the plane’s wings and in front of the engine module are air intakes. However, having intakes on the wing leading edges would be rather poor engineering: tapping off the air before it has a chance to flow over the wings would seriously reduce lift. Nevertheless, Orion is probably the most believable spaceplane ever depicted in any block-buster movie.

The most famous space fighters of the movies, the Star Wars’ X-wing and Battle Galactica’s Viper, have wings and very apparent air intakes but spend most of their time in the vacuum of space. Even so, they seem to require only very small amounts of propellant as there are no large tanks to be seen. This does not seem to make sense: if you can fly and maneuver in space for hours without any external airflow, why bother with air intakes and wings for the brief periods in an oxygen-rich atmosphere? Moreover, these vehicles seem to maneuver in space as if they were flying through air, banking into nice round turns, flying in loops etc. In space there are of course no aerodynamic lift and drag forces, making such maneuvers only possible with the help of a serious set of reaction control thrusters which aren’t apparent in these fictional designs. Moreover, such airplane-like actions are rather useless in space (but not in a movie, as it certainly looks more exciting than real orbital mechanics).

Fireball XL5, a spaceplane shown in the British 1962-1963 television series of the same name also lacks apparent propellant tank volume, but according to the series it is powered by a “nutomic reactor” that enables it to have a range of many lightyears. Although the Fireball is a fictional vehicle without any regard for the limitations of real spaceflight, it is interesting to note that it takes off using a rocket powered sled and a mile-long launch rail that culminates in a 40 degree “sky ramp”, whereupon the spacecraft uses its own propulsion to ascend into space; very similar to the take­off mode of Sanger’s Silverbird.

In reality, even although serious work on orbital spaceplanes has been underway since before the Second World War, they still only fly in the realms of fiction. Like most of the hardware depicted in 2001, A Space Odyssey, nothing like an Orion III was available in the real year 2001; nor in 2011 for that matter. Only the videophone used the movie is actually better in today’s reality. In general, science fiction often overlooks the complexity of spaceplane transportation, and especially the limitations of propulsion technology. Of course, with engines working on fantasy and built out of unobtainium, anything is possible. What the spaceplanes of the movies do show us, however, is the ultimate goal of the real-world launch business: airline-like flights into space.

While engineers in Germany, Russia and Japan were busy building experimental rocket propelled interceptors and designing concepts for even more advanced rocket aircraft, very little work was done on this subject in the United States and the United Kingdom. The success of Allied conventional fighter planes in gaining air superiority over European and Japanese territories gave no incentive to investigate the potential of rocket planes.

The first rocket research to receive financial assistance from the US government was the development of solid propellant RATO (Rocket Assisted Take-Off) units for aircraft by the Rocket Research Group of the Guggenheim Aeronautical Laboratory at the California Institute of Technology (GALCIT). On 12 August 1941 a tiny Ercoupe sports plane piloted by Captain Homer A. Boushey Jr., was fitted with such a solid propellant booster and launched from March Field in California. The booster burned for 12 seconds and gave a thrust of only about 130 Newton. In a later test the RATO unit exploded during level flight. The Ercoupe made a safe landing, but there was clearly something not entirely right with the propellant. On 16 August, Boushey nevertheless took off in the Ercoupe with six RATOs firing. The next step was to get the plane airborne by rocket thrust alone, and this was achieved on 23 August. The propeller was removed and 12 RATO units were fitted. The little plane was towed to a speed of about 40 km per hour (25 miles per hour) by a truck and then the rockets were ignited. Although only 11 units actually fired, the Ercoupe left the ground and reached an altitude of about 6 meters (20 feet).

After these flight tests the team discovered that RATO units tended to explode if they were stored for several days instead of being used immediately after production. The propellant grain shrank and caused cracks and openings to develop between the propellant and the casing, and these caused sudden destructive surges in the internal pressure. Once it became clear that this problem could only be solved by using a new type of propellant, the team developed an innovative solid propellant which was a paste created by mixing black gunpowder with common road asphalt. Its mechanical properties were much more stable under various storage conditions than those of the earher powder propellant. Another major advantage of this composite propellant was that it could be cast into a predetermined shape, allowing propellant grains with pre-programmed thrust-over-time profiles (more or less equivalent to throttling a liquid propellant engine). This provided the basis for the sohd propellants for all later large solid propellant rocket motors, including those on the Space Shuttle.

Based on the new propellant (called GALCIT 53) the team managed to deliver on a Navy contract for 100 RATO units capable of prolonged storage in hot deserts as well as arctic conditions and then delivering a thrust of 900 Newton for 8 seconds. Shortly thereafter, production of operational units for the Navy began at the Aerojet

Engineering Corporation, a company set up by the GALCIT rocket research team for the commercial exploitation of their work.

Surprisingly, the only real American rocket aircraft under development during the Second World War was not an interceptor such as the German Me 163 or Japanese Syusui, nor even an experimental research aircraft like the Russian Florov 4303, but more like the rather desperate German and Japanese back-against-the-wall, last- stand designs for ramming aircraft. In 1942 John K. Northrop, the famous aircraft designer with a fascination for ‘flying wings’, came up with the idea for a fighter which would be sufficiently sturdy that it could slice right through an enemy bomber. His ‘Flying Ram’ was a tailless flying wing built like a knife, with a reinforced leading edge over most of its span and no vulnerable air intakes. Northrop intended it to be powered by an Aerojet XCALR-2000A-1 ‘Rotojet’ liquid propellant rocket engine (which did not yet exist) delivering a thrust of 9,000 Newton. Its take-off was to be assisted by a pair of 5,000 Newton thrust solid rocket boosters which would be dropped once airborne. The engine would run on mono-ethylaniline fuel and red fuming nitric acid oxidizer; a combination that we would not nowadays consider suitable for a manned military aircraft because it is rather toxic. Moreover this fuel would be especially corrosive to the innovative magnesium alloy structure which was to make the aircraft especially sturdy and resistant to damage. Northrop wanted the pilot to lie prone in the cockpit, in the expectation that this would enable him to survive the violent collision with an enemy plane. Moreover, this would make the flying wing much flatter so that the 8.5 meter (28 feet) wingspan would, seen from the front, present a minimum silhouette that would be difficult to hit by gunners in the targeted bomber and also enable it to more easily slice through the bomber.

Northrop managed to interest the US Army Air Forces (USAAF, forerunner of the US Air Force) in the project although at that time there was no obvious requirement for such a radical defense against enemy bombers. Perhaps intelligence forewarning of the secret long-range bomber developments underway in Germany was behind the support for this wild idea. In January 1943 the USAAF issued the Northrop company a contract for three rocket propelled prototypes under the designation XP-79, but in March it was decided to equip the third prototype with a pair of Westinghouse 19-B turbojets as the XP-79B. Similar to the development logic implemented in Germany, Japan and Russia, ghder test vehicles were built to verify the aerodynamics of the aircraft design. Two prototypes (designated MX-334) were pure gliders but the third (designated MX-324) was fitted with an Aerojet XCAL-200 rocket engine that used mono-ethylaniline and red fuming nitric acid. Its thrust of 900 Newton was rather puny compared to the 17,000 Newton of the engine that was at that time propelling the Me 163B in Germany, and a clear indication of how far US rocketry was lagging behind the developments in Germany, Russia and Japan. The airframes of the gliders consisted of a center section of metal tubing covered with plywood, wooden wings, and a fixed tricycle undercarriage.

Flight tests of the MX-334 glider, towed into the air by a P-38 Lightning fighter, showed the flying wing to be rather dangerously unstable even after the addition of a simple vertical fin that was held in place using metal cables. On one flight, the glider got caught in the propeller wash of the tow plane just after release, which caused it to suddenly pitch up, stall and enter a spin. Test pilot Harry Crosby managed to recover from the spin but ended up flying inverted. Finding himself lying on the roof of the cockpit unable to reach the controls, he managed to open the hatch and parachute to safety. The MX-324 was tested at Harper Dry Lake in the Mojave Desert of southern CaUfornia, where secret airplanes by both the Hughes and the Northrop companies were tested. On 20 June 1944 ground tests of the rocket motor were started, followed by taxiing tests with Crosby at the controls. On 5 July the engine and the plane were deemed flight-ready. He eased himself into a prone position in the cramped cockpit with his head in a sling to enable him to look ahead through the large windshield. In front of him he saw the P-38 that was going to tow him to release altitude. The two planes took off and climbed up to 2.5 km (8,000 feet), where Crosby triggered the towline release, then braced himself as he pressed the engine ignition button on the control stick. The thrust was very modest but still resulted in an acceleration of 0.08 G due to the plane’s low total mass of about 1,130 kg (2,500 pounds). When the engine ran out of propellant after 4 minutes, Crosby glided the plane down to a gentle landing on the dry lake. Thus the MX-324 became the first true US rocket propelled aircraft to fly (fully five years after Germany’s He 176). Several more flights were conducted, some equipped with transmitters that sent flight test data to ground-based recorders: an early use of telemetry that would

eventually enable test engineers to monitor in real time how an airplane prototype was performing.

The actual XP-79 rocket plane was never built. Delays in the development of the complicated Rotojet rocket engine, which could never be made to work at full scale, eventually led the USAAF to cancel the XP-79. The development of the jet-powered XP-79B continued. On 12 September 1945 Crosby finally took the XP-79B up from Mojave’s Rogers Dry Lake (later to become famous as Edwards Air Force Base). All was well for about 15 minutes, then the plane suddenly entered a spin from which he could not recover. Crosby failed to bail out and was killed when the plane struck the desert floor. The magnesium alloy structure was almost completely consumed by the resulting fire. After this disaster the USAAF decided to abandon the project. Flying wings like the MX-334 and the XP-79 were signature designs of Northrop and had many advantages over more conventional aircraft shapes, but they proved difficult to fly. Only when sophisticated control electronics became available did a flying wing finally become operational as the Northrop Grumman B-2 Spirit stealth bomber in 1997.

In the United Kingdom rocket aircraft developments were even more modest. A launch sled propelled by solid rocket motors was developed to ‘catapult’ especially modified Hurricane fighters dubbed ‘Hurricats’ off the bows of merchant ships as a means of protecting convoys from marauding German Condor long range bombers. Steam catapults, as used to launch small float planes from Navy ships, were too weak to get the heavy fighter airborne. The Hurricat was a stop-gap measure, as the plane could be used only once: after its mission it had nowhere to land and the pilot had to bail out or ditch his aircraft as near as possible to the convoy that he was defending, and hope that one of the ships would pick him up.

By the mid-1980s it had become clear that a spaceplane based on rocket propulsion only was very difficult to achieve, and that introducing airbreathing engines for at least part of the flight would be necessary. Whilst a single-stage orbital rocket plane must consist of at least 90% propellant, for an efficient airbreathing spaceplane this drops to less than 70%. In other words, for the same payload and propellant weight the structure weight of an airbreathing spaceplane can be more than tripled to over 30% instead of 10% of the overall weight. The dramatic relaxation of this constraint just might make a single-stage spaceplane possible, although it would require a propulsion system significantly more complex than a pure rocket design.

In Germany in 1985, Messerschmitt-Bolkow-Blohm (MBB, with which Junkers had been merged in the meantime) revived the idea for a two-stage, horizontal take­off and landing (HTHL) spaceplane. They named the new concept the ‘Sanger-IF, and its goal was to lower the launch price of satellites and other cargo by a factor of three to ten. As with the Sanger-I it would involve a large, delta-winged hypersonic carrier aircraft and a smaller orbital vehicle, but the carrier would take off from a regular runway and instead of rocket engines it would use airbreathing turboramjets with liquid hydrogen as fuel. Since no oxidizer would be carried, this would result in great mass and volume savings. However it required five very complicated engines that would work as turbojets at speeds up to Mach 3.5 and then as ramjets at higher velocities (the Lockheed SR-71 Blackbird had turboramjet engines but the Sanger-II carrier would be required to fly much faster than the SR-71’s top speed of Mach 3.2). It would be 84 meters (275 feet) long and have a wingspan of 41 meters (135 feet). After taking off from a runway in Europe the carrier aircraft would fly at Mach 4 to

the appropriate latitude for its intended orbit (typically south of Europe, closer to the equator) at an altitude of 25 km (82,000 feet) in order not to pollute the critical ozone layer of the atmosphere. Next it would accelerate to Mach 7 and fly up to an altitude of 31 km (100,000 feet) to release its upper stage, which would use its own rocket engine (burning liquid oxygen and liquid hydrogen) to continue into orbit while the carrier glided back to base. In a modified form the first stage would also be able to function as a hypersonic airhner capable of flying 230 passengers at a top speed of Mach 4.4 for a distance of 11,000 km (6,500 miles); e. g. Frankfurt to Cape Town in under 3 hours. The upper stage would either be a non-reusable, unmanned ‘Cargus’ with up to 15,000 kg (33,000 pounds) of payload, or a HORUS reusable shuttle with a two-person crew and either 36 passengers or 3,000 kg (7,000 pounds) of cargo. The maximum lift-off weight of the Sanger-II would be 350,000 kg (770,000 pounds).

The German government funded a concept study in order to refine the design, as well as a technology development program that led to ground runs of Europe’s first turboramjet engine at MBB in 1991. However, it was concluded in 1994 that full development would be much too costly and the operational launch cost savings in comparison to those of expendable launchers too uncertain, so the entire project was canceled. All that seems to be left are a large scale model of the spaceplane and a laboratory-sized ramjet demonstrator, both of which are on display in the German Technik Museum Speyer (close to the jet-engined Buran shuttle).

The Sanger-II project was part of a kind of spaceplane revival that began in the mid-1980s and ended abruptly in the mid-1990s. This renewed interest was prompted by the rationale that something new was required in order to cut the costs of access to space in comparison with uneconomical expendable rockets and the Space Shuttle, and also that the technology necessary for this was now within reach. In parallel with Germany’s Sanger-II the US devoted a lot of effort to the aforementioned NASP, the British worked on their HOTOL spaceplane, and France, Japan and Russia were all independently working on reusable aircraft-like launch vehicles. It appeared that the days of the expendable launch vehicle were finally numbered.

Even as the Space Shuttle was being developed, in the US in the 1970s there were many studies of a possible successor in the form of a single-stage-to-orbit reusable launch vehicle. The intrinsic weight issues led to the conclusion that complicated tri­propellant rocket engines would very likely have to be created for rocket propelled spaceplanes. These would initially use low-energy but high-density kerosene as fuel to generate high thrust for take-off with a limited tank volume, and then low-density but high-energy liquid hydrogen to efficiently accelerate up to orbital velocity. Sled- launch systems such as Sanger envisioned were also seen as a potential solution; for instance the Reusable Aerodynamic Space Vehicle single-stage spaceplane proposed by Boeing, which envisaged using two Space Shuttle Main Engines for propulsion. Rockwell International offered an alternative concept called the ‘Star-Raker’, a delta-winged HTHL SSTO with ten (!) “supersonic-turbofan/air-turbo-exchanger/ ramjet” engines, three large rocket motors and an undercarriage that would be jettisoned and recovered by parachute. The company issued colorful illustrations showing several Star-Rakers at a commercial airport with their hinged noses open to load cargo, thus emphasizing airline-like operations.

The various studies by NASA, the US Air Force and contracted industries in the 1970s led to a classified military program called Copper Canyon (as with most secret military programs the meaningless name was intended to mask what it was about) that ran between 1982 and 1985, and out of which the US National Aerospace Plane (NASP) emerged as the less classified follow-on announced by President Reagan in his State of the Union of 1986. NASP was to lead to an air-breathing scramjet HTHL spaceplane prototype designated the X-30, operational derivatives of which would be able to function as a single-stage-to-orbit launch vehicle, a hypersonic airliner called the Orient Express (somewhat similar to the dual use the Germans had in mind for the first stage of their Sanger-II), or a military Mach 12 reconnaissance plane and/or strategic bomber offering the response speed of a ballistic missile and the flexibility, accuracy and ‘recallability’ of a bomber. (RecallabiUty means that you can change your mind about blowing some place to bits when the bomber is already on its way, something impossible with a ballistic missile.) Early artistic impressions showed an elegant Concorde-like design which looked as sleek and fast as it was intended to become.

The program was jointly run by NASA and the Department of Defense. In 1990 Rockwell International became the prime contractor for its development. By then the spaceplane had grown considerably in weight and size in comparison to the original design of 1984. Having lost its resemblance to the Concorde, it now had a wedge-shaped aerodynamic configuration called a ‘waverider’ (essentially a hypersonic surfboard) with most of the lift being generated by a shock wave compressing the air below the plane. This shock wave, created by the forward fuselage, would also compress the air before it entered the engines, effectively

supplying the scramjets with more oxygen. The aft fuselage formed a gigantic integrated nozzle for expanding the scramjet’s exhaust. There were small wings to trim the aircraft and provide control. Its overall configuration was ideal for efficient high-speed flight but gave poor lift at low speeds and in particular for taking off.

Much new technology was required, including a lightweight, composite-material hydrogen tank and advanced computer programs for modeling the airflow around the aircraft and through the engines. The hydrogen fuel would require to be carried in the form of a slush (liquid and ice mixture) to limit the volume of the propellant tanks and therefore the size, and most importantly weight, of the aircraft’s structure (a kilogram of hydrogen ice has a lower volume than a kilogram of liquid hydrogen). Heat-resisting carbon materials would be needed for the aerodynamic surfaces that would endure temperatures over 1,700 degrees Celsius (3,000 degrees Fahrenheit) during hypersonic ascent and atmosphere re-entry, and titanium aluminide panels for most of the fuselage. A major hurdle was the development of the scramjet in which liquid hydrogen would be injected into the combustion chamber and be ignited by the hot compressed air rushing in at hypersonic speed. The exhaust would primarily consist of water vapor and be environmentally friendly but the decision to use hydrogen as fuel was mainly driven by the need for high performance and high efficiency.

The NASP design incorporated the clever idea of using the atmospheric heating of the vehicle to increase the thrust of its scramjet engines: by circulating hydrogen fuel through the plane’s skin to warm it up prior to injection into the engine the energy generated by atmospheric drag was effectively added to the thrust of the scramjet. At the same time the cryogenic hydrogen flow would cool the aircraft. It was initially believed that this revolutionary scramjet propulsion and temperature control system would make it possible for NASP to reach Mach 25 in the high atmosphere; enough for it to achieve orbit without the need for additional rocket engines. However, as the development progressed it became clear that the maximum speed attainable would be about Mach 17, as at higher speeds the weight of the active thermal control system would exceed that which would be required to add conventional rocket engines and propellant. Hence for NASP to be used as a single-stage-to-orbit spaceplane it would need additional rocket propulsion. In fact, rocket propulsion would be required also to get NASP up to Mach 3 for the scramjets to take over. And rocket propulsion would be required to perform the deorbit maneuver at the end of an orbital mission. To keep the vehicle sufficiently light, it was planned to use a new type of rocket engine that, apart from onboard fuel, would be fed with air liquefied during atmospheric flight by a combination of ram-compression and cooling by liquid hydrogen; an airbreathing rocket engine known as LACE (‘Liquefied Air Cycle Engine’). Updated requirements stated that the X-30 must carry a crew of two and that, although it was an experimental vehicle, it must also be able to deliver a small payload into orbit. Hence rather than a demonstrator, the X – 30 was to be a semi-operational vehicle. It was supposed to be able to fly a mission every 72 hours (compared to a maximum of one per month for the Space Shuttle) and require only 100 workers for its operations. The ensuing fully operational launch vehicle derivative was expected to cut the cost per kg of payload by a factor of ten.

Meanwhile the estimated cost of the full development into an operational vehicle had increased far beyond the originally projected $3.3 billion for a relatively modest technology demonstrator. By the early 1990s the projected cost for the demonstrator was $17 billion and the fully operational launch vehicle would require another $10 to $20 billion (in 2011 dollars those numbers would be close to 27 and 16 to 32 billion, respectively). It was also expected that another two decades of development would be required to master all the relevant technological issues prior to building a working prototype. Moreover, the argument that NASP would enable airplane-like operations that would result in low costs per flight and rapid turn-around times sounded awfully similar to those predicted but never achieved for the Space Shuttle. The use of liquid hydrogen alone would mean a complete departure from conventional airport storage and distribution facilities, essentially ruling out the use of normal airfields because it would be prohibitively expensive to equip a sufficiently large network of them with the required production, storage and handling facilities. The severe cost increase and schedule stretch, uncertain operational benefits, and the necessity to comply with too many (civil space, commercial airline and military) requirements eroded support for NASP below the critical level. In addition, the collapse of the Soviet Union severely reduced the push in the US for ambitious technical and military programs. Inevitably, it was terminated in 1993.

NASP was initially superseded by the Hypersonic Systems Technology Program (HySTP) in which NASA and the Department of Defense continued with technology development on a less ambitious scale, but when the Air Force withdrew in 1995 the development of a US spaceplane pretty much expired.

During the winter of 1993-1994 the Air Force’s Phillips Laboratory conducted a six-week study of an interesting alternative called ‘Black Horse’ which called for a single-stage rocket propelled spaceplane using hydrogen peroxide and kerosene. This non-cryogenic propellant combination is better suited than cryogenic fluids such as liquid hydrogen and liquid oxygen for rapid-reaction launches for military purposes, and furthermore has a much higher density leading to smaller tanks and therefore an overall smaller, lighter aircraft. But it lacks the specific impulse required for a single­stage spaceplane. To compensate for this lack of performance (and made practicable by the use of storable fluids) once the Black Horse was airborne it would rendezvous with a large subsonic tanker aircraft (a converted airliner) for aerial refueling prior to continuing into orbit. The spaceplane would effectively start its flight not from the ground at zero speed but from 13 km (43,000 feet) and Mach 0.85 (a more advanced system could involve a newly developed supersonic tanker able to do the refueling at a much higher speed). As a pure rocket plane the structure weight constraints for this Aerial Propellant Transfer (APT) vehicle where nevertheless severe. And although aerial refueling is standard procedure for agile military jet fighters, doing it with an

84,0 kg (185,000 pound) rocket plane would be a different matter entirely. In early 1994 Martin Marietta investigated a near-term suborbital X-plane with turbofans and liquid oxygen/kerosene rocket engines to demonstrate the APT concept. Flying up to about half orbital speed, Mach 12, this aircraft could fire an expendable upper stage to insert a satellite into low orbit, or use a Sanger-type atmospheric bounce trajectory to fly for long distances or drop bombs. Being about half the size of the Black Horse design it was called ‘Black Colt’. Several people who worked on these studies went on to establish the Pioneer Rocketplane company in 1996 to develop a commercial satellite launcher based on ATP called ‘Pathfinder’. However, they quickly found out that a switch from hydrogen peroxide to liquid oxygen as oxidizer was required to turn Black Colt into an effective launch vehicle. In the late-1990s, just as the size and complexity of the vehicle increased, the intended market of launching constellations of communications satellites evaporated due to develop­ments in less costly terrestrial mobile phone networks. Without a strong demand, the Pathfinder could no longer be pursued.

The British HOTOL (short for ‘Horizontal Take-Off and Landing’) was a concept for an unmanned, single-stage-to-orbit spaceplane able to use ordinary runways. It would require the development of a novel propulsion system that combined turbojet, ramjet and rocket engine elements. As with the Sanger-II and X-30/NASP, it would use hydrogen as fuel and draw upon atmospheric oxygen as much as possible in order to save the weight and volume of oxidizer that the vehicle would otherwise be required to carry.

In 1982 rocket engineer Alan Bond came up with the idea for a new type of engine combining airbreathing and rocket propulsion that he thought would enable a spaceplane to consist of only one single vehicle (like NASP). Around the same time Robert Parkinson of British Aerospace (BAe) was conducting a study of a reusable launch vehicle. Bond’s engine design, the rights for which had by then been bought by Rolls Royce, was combined with BAe’s launch vehicle concept and in 1985 the BAe/Rolls Royce HOTOL project was bom. It became an official national program in 1986 when the government decided to fund a 24 month proof-of-concept study led by Parkinson and John Scott of Rolls Royce.

The design that emerged looked somewhat like a torpedo with small delta wings at the rear, a single moveable fin up near the nose, and air intakes at the aft-bottom fuselage. It would be powered by four of the Rolls Royce RB545 Swallow engines, which in the atmosphere would use liquid hydrogen to pre-cool the hot air entering the engine and thereby make unusually high compression possible. The air initially entering the engine would have a temperature of about 1,000 degrees Celsius (1,800 degrees Fahrenheit) because it would arrive at high speed and then be slowed down almost to a standstill, resulting in almost all kinetic energy being converted into heat. Subsequent compression in the engine for efficient combustion and thrust generation would increase the air temperature even further, so starting off with the hot air would quickly lead to unacceptably high temperatures in the engine. However, using pre-cooling the compression would start with air which had been chilled to minus 130 degrees Celsius (minus 200 degrees Fahrenheit), yielding less extreme temperatures after high compression. In addition, cooling the air would avoid the need for heavy, high-temperature materials in the compressor section of the engine. Some of the now relatively warm hydrogen coming out of the air pre-cooler system would be used to drive the engine’s hydrogen turbopump while the rest would be burned together with the cooled air in the turbojet section of the engine at relatively low speeds and in the ramjet section at supersonic speeds. At an altitude of 26 km

(85,000 feet) and flying at Mach 5 the engines would be switched to pure rocket mode to bum hydrogen with onboard liquid oxygen instead of air. Unlike NASP, there would not be any scramjet. The return flight would be completely unpowered.

From the very start, HOTOL was to be able to fly into space and back completely automatically, without a crew and with limited contact with ground control stations. Any astronaut passengers would merely be payload in a special container that would fit into the cargo bay located in the middle of the fuselage.

The development of HOTOL soon came up against a typical spaceplane issue that must have also plagued NASP and Sanger-II: the large movement of the center of gravity as the flight progressed. Most of the propellant was housed in the forward and center fuselage whilst the heavy and fixed weight of the propulsion system was all necessarily placed at the aft end of the vehicle. This meant that the plane’s center of gravity moved significantly aft as propellant was consumed. At the same time the large range of Mach numbers meant the aerodynamic center of air pressure moved significantly during the flight: it being aft while accelerating during the ascent, and forward while slowing down upon return. Another complicating factor was that the plane would take off with virtually full tanks but would later approach the airport and land with empty tanks and very little payload, so the center of gravity would thus be completely different at the same relatively low velocities at the start and the end of a mission. Balancing the centers of gravity and pressure became very tricky for the HOTOL lay-out, forcing the designers to modify the fuselage and to locate the wings far aft in order that their lift could counteract the weight of the engines and keep the plane stable at all speeds and propellant loads. But the new configuration that solved the balancing problems required a reduction of the payload. This was compensated by abandoning the conventional aircraft take-off in favor of a rocket propelled trolley (resulting in a similar take-off approach to that Eugen Sanger had in mind for his Silbervogel). This was a serious departure from the originally envisaged aircraft-like operations capability and significantly lowered the commer­cial attractiveness of the project. And when the design team nevertheless found that they had to resort to all manner of untried, experimental materials and structure technologies to maintain a decent payload at a reasonable flight price this caused the government to withdraw its support in 1988, and shortly thereafter Rolls Royce also pulled out. In an effort to save the project in 1990 BAe approached the Soviets to study launching a HOTOL-derived vehicle off the back of their Antonov An-225 (as planned for their MAKS concept). This so-called ‘Interim HOTOL’ would also abandon the complex RB545 engines and instead use conventional rocket engines, possibly of Russian pedigree. Thus HOTOL would become a pure rocket plane launched by a subsonic carrier first stage that would release it at an altitude of 9 km (30,000 feet) and a starting velocity of about Mach 0.7. Antonov also studied the possibility of fitting the An-225 with two additional jet engines (turning it into an An-325) to carry a larger version of the vehicle. But neither the UK government nor the European Space Agency expressed any serious interest and the disintegrating USSR could ill afford to participate, so in 1992 the project was canceled.

Whereas Sanger-II was to be a jet-engined hypersonic carrier aircraft for a rocket propelled upper stage, and NASP was initially conceived to be an airbreathing-only hypersonic spaceplane, the original HOTOL was to fly itself into space using rocket motors and would therefore have been a real rocket plane in that respect (albeit with additional jet propulsion). On the other hand it was to fly unmanned, making it more like a missile than a plane capable of being controlled by a pilot at will. For these spaceplanes the distinction between a jet aircraft, a pre-programmed launcher and a rocket plane becomes rather ambiguous.

The Soviets also had their own aerospaceplane projects. From the mid-1970s to the late 1980s the Myasishchev Experimental Design Bureau worked on the MG-19, a rather megalomaniac concept involving a triangular lifting body with a 500,000 kg take-off weight and a 40,000 kg payload to low orbit. It would use turbojets and then scramjets to get to Mach 16, and subsequently rocket propulsion with hydrogen fuel superheated by a nuclear reactor to achieve orbit. The complexity of the vehicle, the dangers involved in flying a nuclear reactor in a hypersonic aircraft, and the priorities of the Buran space shuttle project meant that by the 1990s this project was gone. The idea of using nuclear power in a spaceplane was not new (since the aforementioned Martin Astroplane with its nuclear magnetohydrodynamic engines had already been proposed in the US in 1961) but it is surprising that Myasishchev still considered it to be a sane solution as late as the 1980s.

The USSR’s specific response to NASP was the Tupolev Tu-2000, a long-range heavy bomber and single-stage-to-orbit vehicle whose turbojet/scramjet/rocket engines used liquid hydrogen and liquid oxygen. Development of this spaceplane started in 1986, aiming for an initial experimental two-person design called the Tu – 2000A that would be capable of reaching Mach 6. After the collapse of the Soviet Union work continued in Russia with two tests of an experimental, sub-scale scramjet at subsonic and supersonic speeds up to Mach 6 using S-200 tactical missiles in 1991 and 1992. However, in 1992 the project was suspended owing to a lack of funds. From the few concept images available it appears that the Tu-2000 would have looked very similar to NASP.

In Japan some spaceplane development was ongoing during the late 1980s and early 1990s under the designation ‘Japanese Single Stage To Orbit’ (JSSTO). Four LACE propulsion units were to drive the vehicle to Mach 5, then six scramjets would accelerate it to Mach 12. Further acceleration to orbital speed would also be achieved using the LACE engines, but now being above the ‘sensible’ atmosphere the engines would be fed air that was liquefied and stored in tanks earlier in the ascent, a process called ACE (‘Air Collection Engine’). Mitsubishi Heavy Industries tested a sub-scale scramjet in a hypersonic wind tunnel in 1994 but the work does not seem to have progressed much further than that.

In a research effort named STS (Space Transportation System) 2000, Aerospatiale in France in the late 1980s and early 1990s investigated a single-stage ramjet/rocket spaceplane that looked similar to the Concorde, as well as a Sanger-II-like concept in which a ramjet/rocket aircraft carried a rocket propelled second stage spaceplane that would be separated at Mach 6. Another French company, Dassault Aviation, worked on a Mach 7 scramjet aircraft that would air-launch an expendable Ariane 5 second stage carrying a Hermes-derived shuttle. This was called STAR-H, for ‘Systeme de Transport spatial Aerobie Reutilisable – Horizontal’ (i. e. airbreathing reusable space transportation system for horizontal take-off and landing). These French concepts were not particularly new, all resembling (aforementioned) ideas from the mid-1960s such as the European Space Transporter, the Dassault Aerospace Transporter and the various two-staged spaceplanes studied by the British Aircraft Corporation.

Of all the spaceplane projects of the 1980s, NASP, a single-stage-to-orbit vehicle with (at least initially) only airbreathing propulsion, appears to have been the most ambitious and most complex. Nevertheless, despite the large amount of technology development that was carried out, not much of this is in the public record; the project was so advanced that even today many of its details remain secret. The Sanger-II was theoretically the least complex by using two stages instead of the more constraining single-stage-to-orbit approach and incorporating airbreathing and rocket propulsion in two separate vehicles. Sanger-II’s first stage would not fly fast enough to require exotic thermal protection materials and scramjets; conventional titanium panels (with additional carbon layers at the hot-spots) and relatively simple ramjets would suffice. During re-entry, the vehicle, being mostly large and now empty tanks, would have a significantly lower density than the Space Shuttle Orbiter (hence a larger surface area in comparison to its weight) and so would encounter relatively benign temperatures. In contrast to NASP it would have been able to put substantial payloads into orbit and operate as a real launch vehicle, potentially beating everybody else to the market. However in the end all of the spaceplane concepts proved to be too far ahead of their time: scramjet and combined propulsion technology was not yet sufficiently developed and the computer programs for simulating airflow and combustion at high speeds and temperatures were not mature enough. An article on NASP in the magazine Flight International in October 1987 had already included an ominous warning: “The odd thing is that the excitement is based almost entirely on theoretical research and small-scale laboratory work. Nobody has run a Mach 25 scramjet continuously for more than a few seconds, and no powered atmospheric vehicle has attained anything like the speeds envisioned for NASP.” Nevertheless, in March 1992 Popular Mechanics enthused “Space Race 2000 is on”, anticipating one of the international spaceplane contenders developing a real vehicle by the turn of the century. But by the mid-1990s all the spaceplane projects had more or less gone: the ideal, airliner-like spaceplane as described in the Introduction of this book was (and still is) a long way off.

Part of the issue is that whereas for a conventional aircraft the design can be split into elements like fuselage, wings and engines, and each can (to some extent) follow an independent development track, a spaceplane requires a fully integrated approach in which any small change of one item can have dramatic implications for the rest of the design. For HOTOL for instance, it turned out that for each additional kilogram of inert weight that the vehicle design gained (say, an additional piece of electronics or thermal insulation) some 25 kg of additional propellant would be needed to restore the vehicle’s performance; and additional tank and structure mass would be required to house this extra propellant, which itself further increased the overall weight. It was a vicious circle. Another parameter with a dangerously strong growth factor was the specific impulse of the rocket propulsion, where a change of just 1 % would impose a 4% change in the gross lift-off weight. Therefore a slight increase in rocket engine performance would pay off but over-optimism concerning the engine’s performance could make the vehicle considerably heavier, larger and more expensive. Accepting a slight reduction in speed to compensate for weight growth is possible in the design of normal aircraft, but a no-go for a spaceplane that needs to achieve a fixed minimum velocity if it is to enter orbit. As only 3% of HOTOL’s take-off weight would consist of payload, it would not require many design changes to consume all of this weight allocation for useful cargo and thus render the vehicle completely useless. The Concorde had a 5% payload but its design was considerably less sensitive to changes because it flew much slower than HOTOL and had more scope to trade-off between payload, speed and range; flying slightly slower than originally envisaged does not a ruin an aircraft design, but for a spaceplane it means the difference between achieving orbit or not.

The very high sensitivity of its performance to the input assumptions makes the design of a single-stage-to-orbit vehicle particularly difficult, and obliges engineers to pay very close attention to the fine detail. It also requires that a wide range of new technologies be advanced to maturity before the spaceplane design can be finalized, because any small discrepancy in expected weight or performance can have major consequences for the entire vehicle design. All this, plus the need to make the vehicle easy to maintain and operate, makes clear just how daunting the task of developing a spaceplane is.