From almost the first flight of the Space Shuttle in 1981, NASA realized that it would need to replace its fleet in the first part of the twenty-first century. Understanding that it took almost a decade to build a new space vehicle, NASA pursued several efforts to replace the shuttle in the 1980s and 1990s.
In the 1980s NASA worked with the DoD on a single-stage-to-orbit (SSTO) vehicle for human space access. If there is a “holy grail” of spaceflight it is the desire for reusable SSTO technology, essentially a vehicle that can take off, fly into orbit, perform its mission, and return to Earth landing like an airplane.
This is an exceptionally difficult flight regime with a myriad of challenges relating to propulsion, materials, aerodynamics, and guidance and control. Fueled by the realization the Space Shuttle could not deliver on its early expectations, DoD leaders pressed for the development of a hypersonic spaceplane. With the beginning of the administration of Ronald Reagan, and its associated military buildup, Tony DuPont, head of DuPont Aerospace, offered an unsolicited proposal to the Defense Advanced Research Projects Agency (DARPA) to design a hypersonic vehicle powered by a hybrid integrated engine of scramjets and rockets.
DARPA program manager Bob Williams liked the idea, and funded it as a “black” program code-named “Copper Canyon” between 1983 and 1985. The Reagan administration later unveiled it as the National Aero-Space Plane (NASP), designated the X-30. Reagan called it in his 1986 State of the Union Address “a new Orient Express that could, by the end of the next decade, take off from Dulles Airport and accelerate up to twenty-five times the speed of sound, attaining low earth orbit or flying to Tokyo within two hours.”
The NASP program initially proposed to build two research craft, at least one of which should achieve orbit by flying in a single stage through the atmosphere at speeds up to Mach 25. The X-30 was intended to use a multicycle engine that shifted from jet to ramjet and to scramjet speeds as the vehicle ascended burning liquid hydrogen fuel with oxygen scooped and frozen from the atmosphere.
NASP never achieved anything approaching flight status. It finally fell victim to budget cuts in 1993, in part as a result of the end of the Cold War. But it also ended because of its technological overstretch. For instance, NASA futurist and longstanding advocate of SSTO Ivan Bekey called NASP “the biggest swindle ever to be foisted on the country” because it “was full of dubious aerodynamic claims and engine performance claims and thermal claims.”
Although the program never came near to building or flying hardware, NASP contributed significantly to the advance of materials capable of repeatedly withstanding high temperatures (on the vehicle’s nose and body) or capable of tolerating repeated exposure to extremely low temperatures (the cryogenic fuel tanks). By 1990, NASP researchers had realized significant progress in titanium aluminides, titanium aluminide metal matrix composites, and coated carbon-carbon composites. Moreover, government and contractor laboratories had fabricated and tested large titanium aluminide panels under approximate vehicle operating conditions; and NASP contractors had fabricated and tested titanium aluminide composite pieces.
By the time of its cancellation, the government had admitted to making a $1.7 billion investment in the National Aerospace Plane, but parts of the R&D was highly secret and the official costs were probably somewhat higher.
There have been four major challenges still vexing efforts to develop a viable hypersonic flight vehicle:
- Guidance and Control.
In the first realm of aerodynamics, through a succession of projects and studies many of the roadblocks to effective shapes for a hypersonic vehicle have emerged. Many of the aerodynamic questions are now satisfactorily understood. The same is true for the second challenge of guidance and control. Materials remains an important aspect yet to be resolved as researchers continue to research heat-resistant materials and composites that can reduce weight. But the biggest issue remains propulsion. There is, as yet, no fully operational scramjet engine, although recent X-43 tests suggest that a break-through is possible in the near term.
The aerospace plane concept that NASP research fostered has enormous promise and may well find reality within the first half of the twenty-first century. This is a critical step in opening the space frontier in the twenty-first century, and perhaps we will return to this concept in the near term.
To achieve this vision will require the pursuit of a new SSTO flight research program. Does anyone think this might happen in the next decade? I hope so. Of course, if Aviation Week & Space Technology is to be believed a spaceplane named “Blackstar” began flying missions as early as 1990. If so, although I doubt it, the influence of NASP may have a much broader importance than most people realize.