During the late 1980s and early 1990s, the United States was actively searching for a way to reach orbit with an integrated scramjet powered vehicle. This eventually took the form of the X-30, commonly known as the National Aerospace Plane. It used a highly integrated propulsion system and structure to allow hypersonic speeds just inside the atmosphere.
The motivations behind the X-30 were two-pronged. If the required technologies could be matured, then the X-30 would serve as the prototype for not only a hypersonic airliner, but also a single-stage-to-orbit spaceplane. As an airliner, it would amount to the modern day version of the Orient Express, greatly reducing flight times between the world's largest cities. The Orient Express would not enter space per se but would hurtle hypersonically through the upper atmosphere using its integral scramjet engines and hydrogen fuel supply, at a speed between Mach 10 and Mach 15. The shovel-shaped air intake would create a large shock wave to compress the airflow prior to entering the combustion chamber. Likewise, the integral aft-body and nozzle would efficiently expand the exhaust products to the rear. The X-30 was to have been a waverider, effectively riding on its own compression shock wave, like a surfer at the beach. The phenomenon of compression lift, which promised greater lift and lower drag, would allow this. The X-30 had a lifting body design and was expected to endure temperatures of 1,800-3,000°F. The project was eventually abandoned in 1993 because of the huge costs in developing the structural materials to withstand the excessive thermodynamic loads at scramjet operation speeds.4
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