Only a 1/3-scale concept demonstrator was built, “flown” only in a high-temperature tunnel between 1986-1994. This joint effort by NASA, the Department of Defense, and five major contractors explored development of technologies for a new generation of aerospace vehicles for hypersonic cruise in the atmosphere or single-stage-to-orbit using air breathing primary propulsion and horizontal takeoff and landing. Although a full-scale aircraft was never built because Congress ended funding in 1994, the program had expected such a vehicle to fly at Mach 25. The program developed significant advances in high-temperature, carbon-carbon materials, lightweight titanium and beryllium alloys, and high strength, corrosion-resistant titanium-alloy composites. These technologies and the program’s work with supersonic-combustion ramjet propulsion will all be useful to subsequent U.S. aerospace efforts in the hypersonic area.