Orion (ex CEV: "Crew Exploration Vehicle"), was the manned space vehicle in the Constellation programme designed to replace the American space shuttles. It was originally designed to send astronauts to the Moon and from there to Mars, but the Constellation programme was cancelled in October 2010. NASA chose a three-stage development approach in successive "spirals".
Spiral 1 included the development of Orion for low orbit missions, a dedicated heavy launcher (Ares 1, formerly CLV) and appropriate ground systems. In the request for proposal, it was specified that the weight of Orion must not exceed 20 tonnes at launch. NASA had planned an unmanned test flight in 2008. On that date a single team would have been chosen from the competing industrials with the task of achieving a manned flight in 2014.
Spiral 2 was to validate Orion for lunar missions on a 2015-2020 horizon. The vehicle was to have been compatible with two other components, also to be developed: the Earth Departure Stage (EDS), a propulsion system capable of taking Orion from low Earth orbit to lunar orbit, and the Lunar Surface Access Module (LSAM), for the crew to reach the surface and live there for a minimum of four days.
After 2020, Spiral 3 was to provide the extra components needed for lunar missions of several months.