VON BRAUN’S VERTICAL TAKE-OFF ROCKET INTERCEPTOR

Von Braun became fully occupied with the development of the A4/V2 missile at the Army area of the Peenemunde center, but retained his interest in rocket planes. As with the A4, he again tried to sell impractical designs to those who didn’t need them: in July 1939 he proposed to develop a rocket powered interceptor for the RLM. The first design had a cigar-shaped fuselage and straight, tapered wings. His trademark propellant combination of alcohol and liquid oxygen was stored in tanks behind the cockpit. The rocket engine was installed in the tail, and just as with his A3 and A4

rockets he placed four rudder-like jet vanes behind the nozzle to divert the exhaust jet and steer the vehicle by thrust vector control. Tilting the two opposing horizontal vanes up or down in the same direction would make the plane pitch, while the two vertical vanes would control the yaw. Rolling could be achieved by tilting opposite vanes in different directions. The pilot was to be seated in a pressurized cockpit that would be able to maintain a comfortable air pressure at high altitudes, and he would be protected from enemy bullets by armor plating. The vehicle would be armed with either two or four cannon mounted in the wing roots.

Whilst the plane was to land normally, von Braun designed his interceptor to take off vertically. That way the rocket plane could be launched straight up to the target and reach it in minimal time. A simple undercarriage would only require to be able to handle the empty weight of the vehicle at the end of the flight. The airplane was basically a rocket with wings. Yon Braun envisaged large numbers of his planes would be stored vertically in a hangar/launch facility, hanging on the tips of their wings on two rails. When the air raid alarm rang, pilots would quickly board their interceptors via a removable bridge, then the plane and pilot would be rolled out of the building and launched straight off the rails. For the first minute or so, the plane would be remotely controlled from the ground and steered to the target by the help of radar (as was done with conventional air defense fighters). Then the pilot was to take manual control, switch off the main engine and start a smaller rocket motor that would enable the plane to engage enemy aircraft at sufficient speed while using its remaining propellant at a much lower rate. Spewing out rocket planes like a giant candy machine, a strategically placed launch facility would thus be able to quickly swarm enemy bomber formations with heavily armed interceptors. After

completing his attack, the pilot was to glide his plane back to land on a grass field using a built-in skid.

However, the RLM considered von Braun’s concept too impractical owing to the need for liquid oxygen, which was difficult to produce and store, and the specialized launch facilities that had to be constructed and maintained. Such facilities could also be easily identified by the enemy and destroyed by precision bombing. Several years later this fear was shown to be well founded when the elaborate bunkers constructed at the French coast to launch VI and V2 missiles against England were destroyed by bombers, often before they became operational. The reluctance to use liquid oxygen in an operational military rocket system was also valid, as shown near the end of the war by the difficulties experienced in providing the mobile V2 launch systems with this propellant because of the bombing of the production facilities and transporta­tion networks. Another reason that the RLM did not buy von Braun’s proposal was that Germany expected to quickly win the upcoming war using its existing conventional weapons; in 1939 the prospect of large enemy bomber formations venturing far into Germany was not considered to be realistic. Unlike the other objections, however, this particular evaluation would soon be proven incorrect.

Von Braun reacted to the objections by producing a second version of his Vertical Take-Off (VTO) interceptor design. He switched to Visol and SV-Stoff as the rocket propellants because these are easier to store for lengthy periods and are hypergolic, meaning that they automatically ignite upon contact and thus do not need a separate ignition system, as does a hydrogen/oxygen rocket motor. SV-Stoff was mostly nitric acid, which is a very nasty substance; not something a pilot should feel comfortable sitting close to, and especially not in a combat aircraft whose tanks are quite Ukely to be punctured by enemy bullets, but, as we shall see, this was not a major concern in German rocket powered fighter design. Otherwise the new VTO plane was similar to its predecessor, with the vertical tail being a bit smaller and the wings now dihedral for improved flight stability.

Von Braun tackled the RLM’s objections to the need for large ground facilities by proposing to launch his updated design from a mobile system based on a truck which hauled a trailer. These would first be used to transport the plane to wherever it would be needed. Once at the launch location, the truck and trailer would each be outfitted with a sort of tower structure and placed one wingspan apart from each other. A crane would hoist the rocket plane vertically between the two, and rest each of its wingtips on one of the support towers. A small flame deflector would be positioned beneath the rocket nozzle to avoid it burning up the ground or damaging the nearby equipment. In spite of the updated design, von Braun’s VTO interceptor project was rejected by the RLM in 1941 because at that time the war was progressing well for Germany, with its forces continuously on the attack. Expecting the offensive war to finish soon, they saw no need for an interceptor which, because of its very limited range, was only suitable for local defense against intruding enemy planes that were in any case never expected to reach Germany in large numbers.

Undaunted, Von Braun retained his interest in rocket planes, and near the end of the war did launch two A4 rockets fitted with large swept-back wings. The military rationale was to develop a ‘boost-glide’ missile capable of reaching London when

Original drawing showing the launch configuration of von Braun’s updated rocket interceptor.

launched from inland, because at that time Germany was rapidly losing the coastal territory from which it had been launching its A4/Y2 rockets. On 8 January 1945 a winged A4b left launch complex P7 at Peenemtinde but failed in flight. The second attempt on the 24th was more successful: it reached an altitude of 80 km (260,000 feet) and then briefly performed a supersonic glide using its two swept-back wings until one of them broke off. The increasingly chaotic situation in Germany near the end of the war prevented any further flight tests.

The A4b launches were part of a plan to develop an A9/A10 two-stage rocket to attack the United States. This intercontinental ballistic missile was to have a winged, piloted upper stage (resembling the later X-15) to undertake an extended glide phase and accurate aiming. Once the A10 booster was jettisoned, the pilot/astronaut would steer the A9 to its target with the aid of radio positioning guidance from a network
of U-boats along the flight path across the Atlantic. Once confirmed to be on course, the pilot was to use his ejection seat and land by parachute near an awaiting submarine if he was lucky.

Furthermore, Von Braun was planning the A6, which was basically a winged A4 with a pressurized cockpit instead of a warhead, plus landing gear and an auxiliary ramjet engine for continuing flight at extreme speed and altitude after the propellant for the main rocket engine was consumed. It would be launched vertically but land horizontally after gliding down to an airfield. To get funding for developing the A6, which von Braun saw as precursor to a real spaceplane, he offered it to the German military as a photographic reconnaissance aircraft. With an expected top speed of 2,900 km per hour (1,800 miles per hour) and a maximum altitude of 95 km (310,000 feet) he reckoned it would be impossible to intercept. But the Army did not see any urgent need for such an advanced, complicated and expensive machine, and it was rejected.

Von Braun’s original concept for a vertically launched interceptor was also kept alive by Erich Bachem, at that time technical manager of the Fieseler aircraft plant. He proposed two designs for a Fieseler VTO rocket aircraft named the Fi 166-1 high – altitude fighter. It initially involved a modified Messerschmitt Bf 109 from which the propeller and piston engine would be removed and replaced by an aerodynamic nose cover. It was to be launched with its aft belly affixed to a rocket stage with the same

250,0 Newton engine as von Braun’s large A4 rocket, then under development at Peenemiinde. Some sources say the engine of the smaller A5 rocket was to be used, but its 15,000 Newton thrust would not have been capable of lifting the engineless, empty Bf 109 of about 1,500 kg (3,300 pounds) together with a loaded rocket stage. At about 12 km (39,400 ft) the spent rocket would be discarded and parachute back down to be recovered and reused, while the engineless plane would attack enemy bombers during a gliding descent. A modification of this initial concept replaced the Bf 109 with a new, Bachem-designed aircraft which had two Jumo 004 jet engines installed beneath its wings to give the plane an extended flight capability. The RLM deemed the idea impractical. Undeterred, Bachem drafted a plan for a Fi 166-11. He deleted the rocket stage and designed the new two-seat aircraft (which looked very similar to Von Braun’s VTO interceptor but was considerably larger) for a vertical take-off under its own rocket power. As before, the RLM was not convinced of the feasibility and the necessity for such a weapon. When the situation changed later in the war, Bachem revived the idea and developed the much smaller BP-349 ‘Natter’ (discussed later in this chapter). It is also interesting that the concept of launching a plane vertically on top of a large liquid propellant rocket stage would much later be revisited many times for launching winged vehicles into orbit, and is of course the basic concept behind the Space Shuttle.