Joyriding a rocket plane

“Ah, but a man’s reach should exceed his grasp, or what’s a heaven for?” –

Robert Browning

On 4 October 2004 the (unofficial) airplane altitude record of 107.8 km (353,700 feet) established by the X-15 in 1963 was finally broken. Not by a new, large-budget government rocket aircraft but by the privately developed SpaceShipOne rocket plane which pilot Brian Binnie flew to an altitude of 112.0 km (367,400 feet). The project was entirely funded by a private sponsor and the vehicle was developed and flown by a small commercial aircraft company.

This revolutionary development in rocket planes and spaceflight had its roots in the X prize, a $10 million reward announced in 1996 for the first private enterprise to develop and launch a suborbital vehicle. The competition’s rules dictated it had to be capable of carrying three people to the ‘edge of space’, and this, in accordance with International Aeronautical Federation regulations, was defined as an altitude of 100 km (62 miles). An X prize vehicle would give its passengers a thrilling ride, enabling them to view the curvature of the Earth and enjoy several minutes of weightlessness in the same way as experienced by X-15 pilots. To prove its reusability, the X prize organization required the same vehicle to make a second flight within two weeks of the first launch with at most 10% of its dry weight being replaced. In addition to the pilot, it had to be capable of carrying two passengers, but the flights required to win the prize could be made by the pilot only.

The purpose of the prize (in 2004 renamed the ‘Ansari X Prize’ following a multi­million dollar donation from entrepreneurs Anousheh Ansari and Amir Ansari) was to encourage the development of suborbital space tourism and thus kick-start a non­governmental human spaceflight industry. It was modeled after the aviation prizes of the early twentieth century which tremendously boosted aviation, such as the Orteig Prize for crossing the Atlantic that was won by Charles Lindbergh and the Schneider Trophy that encouraged the development of extremely fast seaplanes (the heritage of which was evident in several fighter planes of the Second World War, most notably the Spitfire). Twenty-six teams from around the world declared their participation in the competition, with some intending to employ relatively simple rockets (one even a modern derivative of the A4/V2 design) launched from the ground or slung beneath stratospheric balloons, others choosing rocket powered spaceplanes, and others rather exotic concepts such as pulse-jet driven flying saucers. One group even imagined a do-it-yourself suborbital rocket plane which you would be able to assemble in your own garage and launch from the nearest airfield.

The big surprise, however, was Scaled Composites, the Californian company of famous aircraft designer Burt Rutan, which initially shied away from publicity but in April 2003 revealed a project that was far ahead of its competitors. Not only did the company have a good plan but also real hardware: a fully operational twin-engined turbojet high-altitude carrier plane called the White Knight, a mobile mission control center, a mobile propulsion test facility, and a prototype of the Space – ShipOne air-launched, three-seat rocket plane. The company was by then already known for its innovative small aircraft designs, among them the Voyager aircraft that in 1986 flew around the Earth in just over 9 days without refueling or landing (73% of its weight at take-off consisted of fuel, leading to design constraints somewhat similar to those faced by spaceplane designers).

SpaceShipOne is primarily built using composite materials, a signature of Scaled Composites’ designs, as indicated by the name of the company. The fuselage is bullet shaped, similar in appearance to the X-l. Its stubby wings have a slightly swept-back

SpaceShipOne in a glide flight [Scaled Composites, LLC].

SpaceShipOne carried under the White Knight aircraft [Scaled Composites, LLC].

leading edge, a straight trailing edge, and a vertical fin bearing a single horizontal stabilizer at each wingtip. The total length is 8.5 meters (28 feet), the wingspan is 8.2 meters (27 feet), and the total take-off weight is 2,900 kg (6,380 pounds). Its flight profile resembles that of the X-15 by involving an air-drop, boosted ascent, ballistic trajectory into space, re-entry and glide back to the ground. But it is intrinsically a much simpler aircraft, designed not for cutting-edge research flights but purely as a precursor for commercial tourism flights, and it benefits from an additional 40 years’ of developments in aerodynamics, materials and avionics (as well as the considerable experience of the X-15 program). Although its maximum speed is Mach 3 rather than the X-15’s Mach 6.7 and the mission does not call for extreme speed, it does call for extreme altitude. And whereas the X-15 could not survive a steep descent into the atmosphere and so had to fly a 40 degree ascent and descent trajectory over a horizontal distance of some 500 km (300 miles), SpaceShipOne flies up and down almost vertically so that its entire flight occurs within 40 km (25 miles) of its base. This greatly simplifies its operations by not requiring a large network of ground stations, chase planes and emergency landing sites.

SpaceShipOne is propelled by a single, revolutionary rocket motor which is a mix of a solid rocket booster and a liquid propellant motor. This SpaceDev SD010 hybrid motor uses a solid rubber-like HTPB (hydroxyl-terminated polybutadiene) grain as fuel, but in combination with liquid nitrous oxide (also known as laughing gas). The main benefit over a solid propellant booster is that this hybrid engine can be throttled and shut down at any moment by varying the amount of liquid oxidizer that enters the combustion chamber. Without the liquid oxidizer, it is totally safe from explosion during transport and handling. Furthermore these propellants have a higher specific impulse. The hybrid is also simpler than a liquid propellant rocket engine by having only one valve and redundant igniters. In contrast to the complex

SpaceShipOne flight profile [Scaled Composites, LLC].

SpaceShipOne shoots up under rocket power [Scaled Composites, LLC].

XLR99 engine of the X-15 the SD010 uses only non-toxic, easy-to-handle propellants and it has never failed to start. It has a maximum thrust of 75,000 Newton, a specific impulse of 250 seconds, and a maximum total burn duration of 87 seconds.

Prior to re-entering the atmosphere the plane’s two tail booms and the rear half of the wings fold upward on a hinge that runs the length of the wing. This ‘feathered’ position gives the aircraft a high-drag that allows a safe, stable “carefree, hands-off’ penetration of the atmosphere which greatly reduces aerodynamic and aerothermal loads. For this innovative solution Rutan was inspired by a badminton shuttlecock, which always orients itself correctly with the direction of flight. The cockpit has a spacecraft-like environmental control system and features many windows to provide a good view for the pilot and passengers (although no passengers were carried). The aircraft has three flight control systems: a direct manual control for subsonic speeds, an electric control system for supersonic speeds (where muscle power alone is unable to handle the aerodynamic forces), and a reaction control system for high altitudes. The thrusters emit non-toxic cold gas (there is no combustion involved). State-of- the-art instrumentation provides the pilot with the precise guidance information he needs to manually fly SpaceShipOne during the critical boost and re-entry phases. Flight test data is sent to a mission control center during each flight, where it is recorded for careful post-flight analyses.

The only SpaceShipOne aircraft was registered as N328KF, with N the prefix for US-registered aircraft and 328KF chosen by Scaled Composites to stand for 328 К (for kilo, meaning thousand) feet, corresponding to the 100 km altitude goal (registry number N100KM was already taken).

The White Knight plane, SpaceShipOne’s carrier, is itself an innovative aircraft. It too is made mostly out of composite materials. It has two afterburning turbojets, thin wings that have a total span of 25 meters (82 feet) and two tail booms. Most of the cockpit, instrumentation and other internal equipment are identical to those installed on SpaceShipOne, enabling it to flight-qualify much of the equipment intended for SpaceShipOne, thereby sharing the development costs for the two aircraft. The White Knight could be used as a trainer aircraft for SpaceShipOne pilots. The high thrust from its turbojets with afterburners in combination with the low weight, as well as it enormous speed brakes for rapid deceleration meant that rocket plane pilot trainees could use the White Knight to rehearse SpaceShipOne’s boost flight, approach and landing very realistically.

On 21 June 2004 the White Knight took the diminutive SpaceShipOne with 62- year-old pilot Mike Melvill to an altitude of 14 km (46,000 feet). The spaceplane was dropped into a gliding flight, then fired its rocket motor for 76 seconds. Shortly after ignition of the rocket motor, wind shear suddenly made the aircraft roll 90 degrees to the left. Melvill attempted to correct it and unexpectedly rolled 90 degrees to the right. He then managed to level the plane again and proceed with the steep but still somewhat unstable powered boost to a maximum speed of Mach 2.9. During the rocket bum Melville reported a loud bang that was later reahzed to have been caused by the overheating and subsequent crumpling of a new aerodynamic fairing that had been fitted around the rocket nozzle. Fortunately the fairing’s collapse did not affect the flight. After burn-out of the engine the plane continued unpowered to an altitude in excess of 100 km (62 miles). This coasting phase and the following free-fall back to Earth lasted about 3.5 minutes, during which time Melvill opened a bag of M&Ms and watched them float weightlessly around the cockpit. At the highest point of the trajectory the vehicle’s speed was almost zero. Then it began to fall, accelerating to a maximum speed of Mach 2.9 (the same as its maximum speed going up, as potential energy converted back to kinetic energy). During the fall, the two tail booms and rear parts of the wings were put in a vertical position to achieve the high-drag configuration that facilitated a safe, stable penetration of the atmosphere. The thickening air then decelerated the vehicle, and subjected Melvill to a tolerable 5 G deceleration. The re-entry air temperatures remained less than 600 degrees Celsius (1,100 degrees Fahrenheit) owing to the large area of the underside of the aircraft and the relatively modest velocity. There was no need for heat shields or tiles because the hot re-entry phase was brief and the air at high altitude too tenuous to transfer a lot of heat; the skin of the aircraft remained much cooler than the surrounding air (the X-2 flew its ‘heat barrier’ research flights at similar speeds but at much lower altitudes, while the X-15 and orbital vehicles returning from space endure much higher temperatures as a result of their faster entry speeds). In fact, SpaceShipOne’s structure hardly contains any metal parts. At 17 km (57,000 feet) the wings and tail were repositioned and the aircraft reverted to a conventional glider for its descent to the runway in the Mojave Desert in California.

“It was a mind blowing experience, it really was; absolutely an awesome thing,” Melvill said after landing. With this flight he became the first private civilian to fly an aircraft into space, as well as the first person to leave the atmosphere in a non­government sponsored vehicle. (All rocket aircraft except the early, pre-war rocket – boosted gliders were developed under government contracts for military or research purposes.) Measured by the number of world newspapers that carried the story above the fold, the flight was the second largest news event of the year, being topped only by the capture of Saddam Hussein in Iraq.

Work on Scaled Composites’ suborbital spaceplane concept began right after the X Prize announcement in 1996 and the full development program was initiated in April 2001, hidden from the public and the competitors by the inhospitable Mojave Desert. To finance the project the company got a $30 million grant from Paul Allen, Microsoft cofounder and third-wealthiest person in America. Since the X Prize was $10 milhon, Allen could not expect to get a return on his investment any time soon but he was in it for the sense of adventure rather than for the money. The overall plan was to mature the concept, then sell improved vehicles to a space tourism company. “Spaceflight is not only for governments to do,” Allen said. “Clearly, there’s an enormous pent-up hunger to fly into space and not just dream about it.”

SpaceShipOne made its first captive flight on 20 May 2003 and shortly thereafter Rutan announced the project to the public. After a second captive flight there were seven successful glide drop tests before pilot Brian Binnie made the first powered flight on 17 December of the same year (deliberately marking the 100th anniversary of the first ever powered aircraft flight by the Wright brothers). A short burn of the rocket motor pushed the aircraft to Mach 1.2 and an altitude of 21 km (68,000 feet). The left main gear collapsed due to a roll oscillation upon landing but the damage was minor and Binnie was uninjured. After another glide test flight there was a series of progressively faster and higher flights, culminating in the one in June 2004 that put Mike Melvill into space. During the test program SpaceShipOne also became the first privately funded aircraft to exceed Mach 2. All of the flights took place from the Mojave Airport Civilian Flight Test Center, the runway close to Scaled Composites’ premises. The four pilots that flew SpaceShipOne came from a variety of aerospace backgrounds: Mike Melvill was a test pilot, Brian Binnie a former Navy pilot, and both Doug Shane and Peter Siebold were company engineers. They all trained to fly SpaceShipOne using a flight simulator (like the X-15 pilots) as well as by flying the White Knight and other aircraft produced by Scaled Composites.

After Melvill’s space flight, everything was deemed ready to try for the X Prize by making two such flights within a fortnight. On 29 September 2004 Melvill shot up to an altitude of 103 km (338,000 feet), which was slightly less than planned due to a serious roll instability during the rocket-boost phase, but was still above the 100 km requirement. It was quickly followed on 4 October (specifically chosen to mark the 47th anniversary of the launch of Sputnik) by Brian Binnie’s fully successful flight to the record altitude of 112.014 km (367,500 feet) that won the X Prize for Scaled Composites and also made SpaceShipOne the first privately funded aircraft to exceed Mach 3: when the motor cut off at over 61 km altitude (200,000 feet) the maximum speed was Mach 3.09, an equivalent velocity of 3,490 km per hour (2,170 miles per hour). Melvill and Binnie, the two pilots who flew above the 100 km (330,000 feet) mark were issued the first commercial ‘astronaut wings’ by the US Federal Aviation Administration.

No further flights were made, as the prize had been won and the concept and the technology proven. For commercial space tourism flights, Rutan wanted to develop a larger rocket plane that could seat more passengers and incorporate more

SpaceShipOne in the National Air and Space Museum [Photo by Eric Long, National Air and Space Museum, NASM WEB 10516-2005, Smithsonian Institution].

redundant systems and aerodynamic stability for increased safety. In addition, he did not wish to risk damaging the unique and now historic SpaceShipOne. Since 2005 the small rocket plane has hung on display in the main atrium of the National Air and Space Museum in Washington D. C., between the Wright Flyer, the Spirit of St. Louis and the Bell X-l, and near the first X-15. As a tribute to SpaceShipOne’s achievement, in 2006 a small piece of its carbon fiber material was cut off and launched on the New Horizons probe heading for Pluto. An attached inscription reads: “To commemorate its historic role in the advancement of spaceflight, this piece of SpaceShipOne is being flown on another historic spacecraft: New Horizons. New Horizons is Earth’s first mission to Pluto, the farthest known planet in our solar system. SpaceShipOne was Earth’s first privately funded manned spacecraft. SpaceShipOne flew from the United States of America in 2004.”

A fiberglass replica of SpaceShipOne created using the same molds used to make the original can be found in the AirVenture Museum in Oshkosh. Another full-scale replica is on display in the William Thomas Terminal at Meadows Field Airport in Bakersfield, while a third is in the Mojave Spaceport’s Legacy Park, and a fourth is hanging above the stairs in the main entrance of Building 43 of Google’s Googleplex campus (Google cofounder Larry Page was a trustee on the X Prize board) and a card taped to the nozzle implores, “Attention Googlers: Please do NOT launch. Thanks.” SpaceShipOne also became a popular model rocket, with Estes Industries currently offering several SpaceShipOne models that you can launch from your own back yard repeatedly by replacing the little solid propellant rocket motor.

SpaceShipTwo and White Knight Two [Scaled Composites, LLC],

Rutan’s company has now teamed up with the Virgin Group, famous for its airline and its entertainment and communications companies, as well as its charismatic and adventurous head, Sir Richard Branson. Under the name ‘The Spaceship Company’, the Virgin Group and Scaled Composites have set up a joint venture to develop the SpaceShipTwo and White Knight Two aircraft which will be operated by a company called Virgin Galactic. At the time of writing, the ‘spaceline’ plans to operate a fleet of five SpaceShipTwo vehicles starting no earlier than 2012. They have been taking bookings at $200,000 per passenger for the early flights, and by late 2011 had over 450 paid customers. It is expected that ticket prices will drop significantly as flight operations mature, increasing the size of the space tourist market.

SpaceShipTwo, based on the same principle, concept and shape as SpaceShipOne is roughly twice the size in order to house two pilots and six passengers. It will be propelled by a larger hybrid rocket motor named ‘RocketMotorTwo’ delivering over

230,0 Newton of thrust. Development of the new rocket plane was delayed when in 2007 an explosion occurred during an oxidizer flow test that was being conducted at the Mojave Air & Space Port. Three staff were killed and another three severely injured; rocket engines are still potentially dangerous devices that have to be handled with great care. White Knight Two is an innovative twin-hull aircraft that carries the SpaceShipTwo rocket plane between its fuselages. It is also designed to operate as a zero-G parabolic-flight aircraft for SpaceShipTwo passenger training or micro­gravity science flights, and as a high-altitude research plane. It could potentially launch other rockets than SpaceShipTwo, such as small sounding rockets with instruments for scientific research.

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SpaceShipTwo technical diagram [Virgin Galactic].

Unlike previous rocket plan projects, environmental impact is now an important issue in aviation. With respect to carbon dioxide (C02) emissions the hybrid engine is not exactly ‘green’ but according to Virgin Galactic, “C02 emissions per passenger on a spaceflight will be equivalent to approximately 60% of a per-passenger return commercial London/New York flight.” This is about 500 kg of carbon dioxide per passenger per flight. So even if SpaceShipTwo flights eventually number 1,000 per year the resulting carbon dioxide emissions would be in the order of one-thousandth of what a major airline typically expels into the atmosphere during a year. Virgin Galactic nevertheless accepts that the environmental impact of their operations could have serious implications for the image and success of their business, and the larger Virgin empire is committed to being as environmentally friendly as is practical. The company therefore plans to run its spaceport(s) with as much renewable energy as possible, which may even make them a net energy producer and potentially “carbon negative” by preventing more emissions of carbon dioxide than its vehicles produce. White Knight Two’s jet engines will initially burn kerosene but are also capable of running on butanol, a biofuel that can be made from algae.

The first SpaceShipTwo, christened VSS (Virgin Space Ship) ‘Enterprise’ (after the legendary Star Trek starship) made its first glide flight on 10 October 2010, being launched by the first White Knight Two aircraft VMS (Virgin Mother Ship) ‘Eve’, and it performed its first ‘feathered’ flight on 4 May 2011. To date, a total of 16 glide flights have been made, and round 100 test flights are expected before the first
passengers will be carried. The first commercial flight is expected no earlier than 2012. The company will initially operate from Spaceport America, a brand new $210 million airport for suborbital vehicles located in New Mexico. There are also plans for a sister spaceport in northern Sweden. Singapore and the United Arab Emirates have both also shown interest in establishing suborbital flight facilities.

A SpaceShipTwo flight will be an incredible adventure offering the possibility, albeit brief, to experience what astronauts (and X-15 pilots) feel and see, without the heavy workload. You will be dropped from the carrier aircraft at an altitude of 15 km (50,000 feet) and then go supersonic within 8 seconds. After 70 seconds of powered flight, during which you attain a maximum speed of just over Mach 3 (equivalent to about 3,500 km per hour, or 2,100 miles per hour) the rocket plane will coast to a peak altitude of 110 km (360,000 feet). The virtually drag-free parabolic trajectory will last for 3.5 minutes, during which you will be able to float about in the relatively spacious cabin and admire the view of Earth below and the curvature of the horizon through the large windows.

Other companies are also working on suborbital rocket planes for space tourism, with microgravity science and high-altitude experiments (as on the X-15) forming a secondary market. XCOR Aerospace, which is based on the same Mojave airfield as Scaled Composites, is developing its ‘Lynx’ rocket plane (superseding its earlier and similar ‘Xerus’ design). Unlike SpaceShipTwo this double-delta-winged vehicle will take off from a runway on its own power and hence will not require a carrier aircraft. This simplifies the development and operations (one rather than two planes) but it means the rocket aircraft has to carry all the propellant for the entire flight itself. The Lynx Mark-I prototype aircraft is considerably smaller than SpaceShipTwo and will only be able to reach an altitude of 60 km (200,000 feet) carrying a pilot and a single paying passenger. A more advanced Mark-II production version is to be able to reach the milestone of 100 km (330,000 feet). The passenger will have to remain strapped in his seat, as the cockpit is too small for weightless acrobatics. On the other hand, the initial ticket price announced by the company is about half that of a SpaceShipTwo flight. XCOR appears to be well advanced in the general development of liquid propellant rocket engines, and has reported that its 13,000 Newton XR-5K18 liquid oxygen and kerosene rocket engine (four of which will be needed to power the Lynx) is almost ready for flight. But propulsion is only one part of a rocket plane, and although the company has done extensive wind tunnel testing using a scale model of the Lynx, its announcement that it expects to start the test flight campaign of its Mark-I prototype in 2012 appears rather optimistic.

XCOR modified an existing canard configuration (i. e. tailless) ‘Long EZ’ sports aircraft to demonstrate its rocket engine capabilities by installing two 1,800 Newton restartable, pressure-fed, regeneratively cooled rocket engines which burn isopropyl alcohol and liquid oxygen. This ‘EZ-Rocket’, which is a modest-performance rocket plane in its own right, has made a total of 26 flights including a number of air show demonstrations. In December 2005 the EZ-Rocket set the world record for ‘Distance without Landing’ for a ground-launched rocket powered aircraft with a flight from Mojave to California City, a distance of 16 km (9.94 miles). “That was the shortest long-distance record flight ever!” pilot Dick Rutan exclaimed. XCOR also built and

Artistic impression of the Lynx rocket plane [XCOR Aerospace].

flew the ‘X-Racer’, a sleek rocket aircraft based on the airframe of the ‘Velocity SE’ canard sports plane. This was a prototype for aircraft to compete in rocket plane races organized by the Rocket Racing League, an organization that seeks to promote rocket aircraft development by flying competitions. The X-racer is equipped with an XR-4K14 restartable, pump-fed rocket engine that burns liquid oxygen and kerosene with a thrust of 6,600 Newton. It made its first flight on 25 October 2007. The test program has now been completed after a total of 40 flights and demonstrations. The X-Racer holds claim to several (unofficial) records including the most flights made in a single day by a manned rocket powered aircraft, and the fastest turn-around for a manned rocket powered vehicle.

Armadillo Aerospace, the small aerospace company of computer game developer John Carmack, who made his fortune by developing popular games such as Doom and Quake, has also made a rocket engine for the Rocket Racing League. It equipped the Rocket Racing League’s current Mark-II and Mark-Ill Rocket Racers, which are also based on the Velocity airframe (in this case the Velocity XL FG version) with a home-grown rocket engine that is fed with liquid oxygen and ethanol and develops a maximum thrust of 11,000 Newton. Seven successful test flights were made by the Mark-II aircraft during August 2008 and both machines are currently used for flight demonstrations. The Rocket Racing League hopes to generate sufficient interest for a number of teams to build or purchase similar rocket aircraft in order to participate in rocket propelled air races. In the meantime, you can download a video game that puts you in the cockpit of a Rocket Racer.

EZ-Rocket PCCOR Aerospace].

In March 2002 the Space Adventures company that organizes ‘flight participant’ missions to the International Space Station, unveiled a mockup of the ‘Cosmopolis ХХГ (C-21) lifting body-type suborbital rocket plane at Zhukovskiy Air Base near Moscow. This was to be developed by the Russian Myasishchev Design Bureau, be launched from the design bureau’s existing M-55X ‘Geofizika’ high altitude aircraft, and be able to carry a pilot and two passengers into space at $98,000 per ticket with the first flight in 2004. The carrier aircraft with the C-21 attached would first slowly climb to an altitude of 17 km (56,000 feet) and then gather speed in order to make a vertical climb to 20 km (66,000 feet) to release the C-21. The C-21 would then ignite its expendable sohd propellant rocket motor. When this motor burned out it would separate and fall away, leaving the C-21 to follow a ballistic arc to a peak altitude of 100 km (330,000 feet). The rocket plane would glide back to the airport and make a parachute-assisted touchdown. But Space Adventures has abandoned its plans to use the C-21 and instead contracted Armadillo Aerospace to develop a vertical launched, vertically landing suborbital rocket capsule to implement its planned suborbital flight services.

The giant European space company EADS Astrium announced in 2007 that it was to develop a suborbital rocket plane for space tourism. This single-stage, straight-winged plane would take a pilot and four passengers to the edge of space and offer a great view through many large windows and a roomy cabin for weightless antics. It would take off from a normal airport and climb to an altitude of 12 km (39,000 feet) with jet engines, then ignite a Romeo liquid oxygen-methane rocket

The Mark-Ill Rocket Racer in flight [Rocket Racing League],

engine to reach 60 km (200,000 feet) in just 80 seconds with enough velocity to continue unpowered to its 100 km (330,000 feet) apogee. As the plane fell back the pilot would use small thrusters to control its attitude for re-entry into the atmosphere prior to restarting the jet engines to return to the airport. Jet engines use 10 to 20 times less propellant than rocket motors of the same thrust over the same time and are much more efficient for the first and final phases of a flight (SpaceShipTwo’s carrier aircraft uses jet engines for the same reason) but when they are not providing thrust at high altitudes they are dead weight. SpaceShipTwo effectively leaves them behind once it separates from its carrier. Jet engines are also handy in case of a failure of the rocket engine, as well as for ferry flights between airfields. Astrium expected to require around 1 billion euro to develop their system (much more than SpaceShipTwo is estimated to cost), flights to begin in 2012, and tickets to cost up to

200,0 euro. “The development of a new vehicle able to operate in altitudes between aircraft (20 km) and below satellites (200 km) could well be a precursor for rapid transport point-to-point vehicles, or quick access to space,” the company said.

Artistic impression of the take-off of the EADS Astrium suborbital rocket plane [EADS Astrium & Marc Newson Ltd],

Famous designer Marc Newson was to take care of the aesthetics of the design, and the images in the brochure published by Astrium sure are beautiful. As Astrium builds the Ariane 5 launcher and its mother company EADS develops and produces the famous Airbus airliners as well as the Eurofighter military jet, the company seems ideally suited to pursuing a suborbital rocket plane project: it has all the necessary knowledge, experts and facilities in-house, and could incorporate a lot of existing EADS aircraft and spacecraft equipment such as cockpit instrumentation, undercarriage and control thrusters.

After their 2007 announcement, however, Astrium remained awfully quiet about their rocket plane, making it appear to have been merely a publicity stunt rather than a real project. But early in 2011 the company announced that it was indeed working on the concept and that after having placed work on hold for several years due to the global economic downturn it was planning to spend a further 10 million euro on it in 2011; a considerable sum but not much in comparison with the 1 billion euro that it had predicted for full development. “We continue to mature the concept, maintaining the minimum team in order that when we find the relevant partnership we are ready and have progressed sufficiently,” Astrium CEO Franfois Auque told reporters in January 2011. Once it has secured the required financial and industrial partners, the company expects to be able to put the rocket plane into service within five years.

In 2004 another big European aeronautics company, Dassault Aviation in France, announced its own suborbital rocket plane design called VSH. This was based on an earlier design for an automated air-launched reusable hypersonic vehicle known as YEHRA (‘Vehicule Hypersonique Reutilisable Aeroporte’) but was intended to be manned and therefore VSH stood for ‘YEHRA Suborbital Habite’. The delta-winged rocket plane would be carried into the air by a commercial aircraft, be released at an altitude of 7.6 km (25,000 feet) and a speed of Mach 0.7, and ignite a liquid oxygen-kerosene rocket engine to climb to the milestone altitude of 100 km (330,000 feet). Design work is progressing in the context of the K-1000 project that Dassault is self-financing with several industrial partners in Switzerland.

Bristol Spaceplanes, mentioned earlier for its Spacecab and Spacebus projects, is working on a rocket plane called ‘Ascender’. This is a delta-winged aircraft with two jet engines and a single rocket motor similar in concept to that of EADS Astrium but only able to seat a pilot and a single passenger. Ascender’s rocket engine, a prototype of which is to fly on a sounding rocket, will use hydrogen peroxide and kerosene as propellants. As such it resembles the Spectre rocket engines developed in the 1950s to power the SR.53 and SR.177. Ascender is also to pave the way for the company’s orbital spaceplane concepts (discussed above). However progress is slow because the company is waiting for a serious investor so that it can afford to appoint a full-time team of engineers.

Virgin Galactic would seem to be the most advanced company in terms of making and flying suborbital rocket planes, but if the space tourism market really takes off there ought to be room for several aircraft manufacturers and operators to compete. This would hopefully lower ticket prices further, resulting in ever more people being able to afford a flight to the edge of space.

The next step foreseen by Burt Rutan is an orbital rocket plane for space tourism, but that poses a tremendous challenge because although the 100 km (330,000 feet) altitude reached by SpaceShipTwo will be sufficiently above the atmosphere to circle the Earth a couple of times, the speed of the vehicle falls far short of that required to

Artistic impression of the Ascender rocket plane [Bristol Spaceplanes].

enter orbit. To achieve orbit at that height, a vehicle must have a horizontal speed of

7.8 km per second (4.8 miles per second); i. e. 28,000 km per hour (17,500 miles per hour). SpaceShipTwo reaches Mach 3 at engine burn-out in a steep climb but at the top of its parabolic arc its speed is virtually zero (as all its energy has been converted into altitude). Compared to SpaceShipTwo’s maximum speed of 0.9 km per second (0.6 miles per second) an orbital rocket plane needs to go over 8 times faster; and as kinetic energy increases with the square of the speed that means a propulsion system capable of delivering almost 70 times as much energy! This is why satelhte launchers and orbital spaceplane concepts are so much larger than suborbital rocket planes such as SpaceShipTwo and Lynx; even though they all reach space, in terms of energy and thus propellant volume the difference is huge. Weight constraints are also much more demanding for an orbital spaceplane. Whereas a suborbital rocket plane’s dry weight can be approximately 40% of the vehicle’s overall weight including propellant, the energy needed to go into orbit demands that a plane’s empty weight be no more than 10% of its take-off weight (for both types of vehicle these percentages diminish if multiple stages and/or airbreathing propulsion are employed but the large difference remains). This also has consequences for safety: where normal aircraft structures are usually designed to be able to withstand 1.5 times the highest load expected to occur during the plane’s lifetime (and even 2 times for the undercarriage) this margin will be extremely difficult to meet for reusable orbital spaceplanes. Even for expendable launchers, which are less constrained regarding empty weight, this factor is typically only 1.2, except for crewed launchers where it is 1.4 according to NASA standards.

In short, the difficulty in achieving orbit is not so much to get up to high altitude, it is rather to attain the necessary high velocity with a structure weight that provides a reasonable amount of rehability and safety. Factoring in the much more extreme re-entry temperatures that will require heat shields, and that ‘feathering’ cannot be used for hypersonic re-entry, clearly indicates that an orbital SpaceShipThree will not be merely an upgrade of SpaceShipTwo but a completely new, much larger, and more complicated spaceplane that will be vastly more expensive to develop and operate.