The Rockwell X-30 National Aero-Space Plane (NASP) was an attempt by the United States to create a viable single stage to orbit (SSTO) spacecraft. The project was cancelled prior to the first craft being built.
The program to develop the X-30, had its roots in a highly classified, Special Access Required, Defense Advanced Research Projects Agency (DARPA) project called Copper Canyon, which ran from 1982 to 1985. Originally conceived as a feasibility study for a single-stage-to-orbit (SSTO) aeroplane which could take off and land horizontally, Copper Canyon became the starting point for what Ronald Reagan called, “…a new Orient Express that could, by the end of the next decade, take off from Dulles Airport (Washington D.C.) and accelerate up to twenty-five times the speed of sound, attaining low earth orbit or flying to Tokyo within two hours …”
The next stage of the program, called Phase 2, with Copper Canyon being Phase 1, was intended to develop the technologies for a vehicle that could go into orbit as well as travel over intercontinental ranges at hypersonic speeds. There were no commitments to undertake Phase 3, the actual design, construction and flight testing of the aircraft.
There were six identifiable technologies which were considered critical to the success of the project. Three of these “enabling” technologies were related to the propulsion system, which would consist of an air-breathing supersonic combustion ramjet, or scramjet. A scramjet is designed to compress onrushing hypersonic air in a combustion chamber. Liquid hydrogen is then injected into the chamber, where it is ignited by the hot compressed air. The exhaust, consisting primarily of water vapour, is expelled through a nozzle to create thrust. The efficient functioning of the engine is dependent on the aerodynamics of the airframe, the underside of which must function as the air inlet mechanism and the exhaust nozzle. Design integration of the airframe and engine are thus absolutely critical to project success. The efficient use of hydrogen as a fuel for such a system was another crucial element in the development of the X-30.
Other enabling technologies included the development of advanced materials including various composites and titanium-based alloys which maintain structural integrity at very high temperatures. The enormous heat loads associated with hypersonic flight, sometimes in excess of 1,800 degrees Fahrenheit, would necessitate the development of active cooling systems and advanced heat-resistant materials.
Although the NASP effort was announced by President Reagan in his State of the Union address, much of the project remained shrouded in secrecy. Indeed, the paucity of publicly available information on this project was remarkable. This very high level of classification derived at least in part from the core technological innovation that was the genesis of the X-30 project.
Prior analyses of scramjet propulsion systems had concluded that they would only be able to achieve speeds of about Mach 8. At this speed, the thrust emerging from the rear of the plane would be balanced by the heat generated by atmospheric drag and the high temperature of the air as it entered the front of the engine. Thus limited to a maximum speed that was only one-third the orbital velocity of Mach 25, a scramjet-propelled vehicle would need rocket motors to achieve the remaining speed needed to reach orbit. Analyses concluded that such a vehicle would be heavier and more complicated than a conventional rocket.
However, the Copper Canyon project discovered that higher speeds could be achieved through the imaginative use of active thermal management. By circulating, and thus heating, the scramjet’s hydrogen propellant through the skin of the vehicle prior to injection into the engine, energy generated through atmospheric drag was added to the thrust of the scramjet, enabling it to accelerate beyond the Mach 8 thermal barrier. Initially, there was optimism that this active thermal management approach would permit speeds of up to Mach 25 using air-breathing engines alone, eliminating the need for rocket propellants to achieve orbit.
The mass saved by eliminating the final rocket propellants had to be balanced, however, against the mass of the active thermal management system. This system became more complex and massive at higher speeds. At some point, the additional mass of the thermal management system needed to continue the acceleration of the air breathing scramjet would become greater than the mass of the rocket motors and propellant needed to continue the ascent to orbit.
As the NASP effort began, analysis suggested that this transition speed, at which rocket propulsion would be more efficient than continued scramjet operations, would be quite high, above Mach 20. Although this fell short of the initial promise of Copper Canyon, it nonetheless suggested that a scramjet vehicle might offer superior performance compared to conventional rockets. Over time, however, as the complexity of the active thermal management system was better appreciated, estimates of the transition speed declined to below Mach 17. This diminished performance significantly reduced the attractiveness of scramjet propulsion compared with all-rocket vehicles.
Though the protection of this technological principle may explain part of the secrecy surrounding the NASP program, studies of the missions that such a vehicle might perform remain even more closely held.
Defining the mission of NASP to attract maximum support and funding was a tricky business for program proponents. Original cost projections of US$3.1 billion dollars more than tripled, to a total cost of approximately US$10 billion for the development of a pair of single-stage-to-orbit vehicles.
A decision to undertake Phase 3 flight testing would have brought total program costs up to as much as US$17 billion. The target date for the first test flight of the X-30 was pushed back to the 2000-2001 period, 11 years behind schedule and 500 per cent over budget. Many years and a further US$10 billion to $20 billion would have been required for the development of an operational vehicle. Funding this significant increase in a time of general budget cutting is not easy, and program cost over-runs and delays in scheduling made the project less attractive to many supporters.
Though the X-30 was originally touted by the Reagan administration for its civilian commercial applications and as a possible follow-on to the Space Shuttle for NASA, the funding structure of the program tells another story. The Department of Defense was scheduled to fund approximately 80 per cent of the project, or US$2.65 billion out of US$3.33 billion over the eight years of the original project. Budget allocations come primarily from the Air Force, which saw NASP as potentially having a range of military missions.
The mystery remains of what military mission justified this level of effort. Or perhaps there is no mystery at all. The X-30 may have been the purloined letter of military aircraft: an SR-71 follow-on hidden in plain sight.
Such a possibility would also explain the tenacious position of Congressman Dave McCurdy, the only member of Congress at the time to sit on both the Armed Services Committee and the Space and Technology Committee. From 1989 through 1992, McCurdy fought hard for continued funding for and Air Force involvement in NASP.
“It’s important to remember that NASP is not a NASA program. NASP is not an Air Force program. It is a national program. We believe that it is important to the country.”
Presumably, an SR-71 follow-on would also be a national program of importance to the entire country. These arguments are, of course, predicated on the assumption that the NASP vehicle could fulfil such a defence mission. While the reconnaissance and surveillance mission would be similar to the SR-71, closer examination revealed that the possible military applications provided a less than compelling rationale for the NASP effort.
As a single-stage-to-orbit vehicle with a claimed turnaround time of as little as 24 hours, proponents of the Strategic Defense Initiative initially saw the X-30 leading the way to faster, cheaper access to low earth orbit, a critical aspect of lowering the cost of any space-based ballistic missile defence systems. However, as it became clear that the time required for the development of an operational capability would extend far beyond the time horizon envisioned for deployment of space-based anti-missile systems, the SDI program soon lost interest in the NASP effort. A similar disenchantment emerged within the Air Force and NASA, as the high technical risk of the project became increasingly clear. What also become increasingly clear is that the claims made for NASP as a space launch vehicle were eerily reminiscent of the initial claims made for the Space Shuttle in the early 1970s. The assertions that NASP will have aeroplane-like operating characteristics, with lower costs and fast turnaround times on the ground, are assumptions, rather than conclusions based on detailed analysis.
The potential for using NASP derived vehicles for strategic bombardment, as a hypersonic B-3, did not escape the notice of the Air Force. General Lawrence Skantze, commander of the Air Force Systems Command, observed: “We’re talking about the speed of response of an ICBM and the flexibility and recallability of a bomber, packaged in a plane that can scramble, get into orbit, and change orbit so the Soviets can’t get a reading accurate enough to shoot at it. It offers strategic force survivability – a fleet could sit alert like B-52s.”
The idea of reaching targets anywhere in the world in an hour or two may be a tempting idea, but the challenge of accurately dropping a gravity bomb while travelling 20 times the speed of sound would be non-trivial. Unfortunately, a hypersonic aircraft would have high visibility to hostile defence due to its enormous heat signature and non-stealth composition of the fuselage, resembling nothing so much as a barn on fire. This was hardly a major selling point for a reconnaissance aircraft. As a bomber, a NASP derived vehicle would combine the worst features of an aircraft and a missile. With the large signature of an aircraft and the limited manoeuvrability of a missile warhead, it would provide a ready target for defensive systems.
A third suggested mission for NASP derived vehicles would be as an interceptor for defence of the continental United States. Robert Cooper, Director of DARPA, suggested that it could: “… fly up to maybe 150,000 to 200,000 feet, sustain mach 15 plus for a while, slow down and engage an intercontinental bomber or cruise missile carrier at ranges of 1000 nautical miles…”
But the elaborate preparations needed to maintain a liquid hydrogen fuelled aircraft on alert, combined with the limited manoeuvrability of this type of vehicle, would limit its utility for this mission.
A final application of NASP was as an intelligence collection platform. Robert Cooper suggested that it could provide: “… a globe-circling reconnaissance system, a kind of super SR-71 that would… get anywhere on the Earth within perhaps half an hour of take-off …”
But such reconnaissance and surveillance activities of hypersonic craft are constrained by the high speeds and altitudes at which the X-30 or its derivatives would travel. At altitudes nearly three times that of standard reconnaissance aircraft and a fuel cost three times that of aviation grade kerosene, it would certainly seem more economical to get information of comparable (or better) resolution from a satellite in low earth orbit, which could make another pass in 90 minutes instead of being forced to return to base for refuelling.
Although some proponents have viewed these military missions as potentially attractive, a Committee of the National Research Council expressed doubts about the operational effectiveness of NASP derived vehicles: “Another restriction is inherent in the base support requirements associated with cryogenic fuels. They will require a complete departure from conventional airport storage and distribution facilities. For economic reasons alone, we are unable to envision a network of airfields giving the flexibility that today’s aircraft enjoy.
“Sustained cruising flight in the atmosphere roughly between Mach numbers 8 and 20 … is a very stressful flight environment with high skin temperatures, control and manoeuvring difficulties, ionised boundaries through which sensors must operate, and high infrared signatures which would make the vehicle vulnerable to detection. For these reasons, we have great reservations about the military utility of sustained hypersonic flight in the atmosphere above Mach number 8.”
A draft analysis done at the RAND Corporation was even more pessimistic: “Grave doubts exist that NASP could come anywhere near its stated/advertised cost, schedule, payload fees to orbit, etc. On the basis of current knowledge, it is hard to defend previous Department of Defense plans for NASP on the basis of any singular mission utility sufficiently attractive to operators. NASP could do many missions (but none is singularly persuasive). No compelling “golden mission” exists for NASP.”
NASA was disinclined to significantly increase its share of program costs given its budgetary constraints and the Air Force, which has borne the brunt of development costs of Phase 2, expressed doubts about the future viability of the program. According to Martin Faga, Assistant Secretary of the Air Force for Space: “These are exciting ideas, but they are not ready for commitment.”
Clearly, no single vehicle can serve commercial, civil space and military masters at the same time. In spite of efforts to be all things to all people, the NASP remained without a truly credible mission, and ultimately proponents were unable to save it from termination.
The demands of being a man-rated vehicle, with the instrumentation, environmental control system, and safety equipment, made X-30 larger, heavier, and more expensive than required for a technology demonstrator. The result was a cancellation of the X-30 and a more modest hypersonic program that culminated in the unmanned X-43 “Hyper-X”, which is essentially an unmanned scaled-down X-30. A 50-foot, detailed 1/3d scale mock-up of the X-30 was built by engineering students at Mississippi State University’s Raspet Flight Research Lab in Starkville, Mississippi. The mock-up is on display at the Aviation Challenge campus of the U.S. Space Camp facility in Huntsville, Alabama.