X33, X34, X37, X40A, X42 X-planes RLV compile-set

In early 1990s, US congress requested to reduce funding for Space Shuttle operations. It is difficult for NASA to reduce costs without affecting safety. Many studies suggest that a Reusable Launch Vehicle (RLV) designed for quick-turnaround operation after each flight will allow for costs reduction. In 1994, NASA launched the RLV programs to demonstrate technologies of a new generation of space boosters capable of delivering payloads at lower cost. Lockheed Martin was selected as partner for the X-33 development, and Orbital Sciences won contract for the X-34 program. In 1996, the USAF interested in the RLV concept which has potential to become operational military space plane. A competition calling for advanced RLV started. Boeing won contracts to develop the X-37 launch vehicle and X-40A aerodynamic testbed. The X-40A first drop-tested in 1998. In 2001, due to budget cut, both the X-33 and X-34 were cancelled while the X-33 85% completed and the X-34 took place first unpowered flight. In 2002, Orbital Sciences has presented a design for the USAF's reusable solution to the upper stage requirement. It became the X-42 still-classified space project.