despite progress in the necessary structural and propulsion technology, nasa still had substantial problems to solve. the department of defense wanted it to carry a crew of two and even a small payload. the demands of being a human-rated vehicle, with instrumentation, environmental control systems and safety equipment, made the x-30 larger, heavier, and more expensive than required for a technology demonstrator. the x-30 program was terminated amid budget cuts and technical concerns in 1993.