The X-37 is an unmanned demonstrator spacecraft designed and developed by Boeing’s Phantom Works, US, to meet the requirements of the National Aeronautics and Space Administration (Nasa) and the US Air Force. The spacecraft development is part of the Orbital Space Plane program designed to support the transportation of crew and contingency cargo in Nasa’s International Space Station.

The X-37 is principally used for space exploration, risk reduction and developing reusable space vehicle technologies. It is derived from the X-40A spaceflight and is one of the most modern spacecraft in the world. Fueled with military fuel JP-8 and hydrogen peroxide, the Rocketdyne engine of the X-37 is designed to run for nine months. The engine installed in the aircraft currently uses hypergolic nitrogen tetroxide or hydrazine.