Founded in 1999, XCOR Aerospace was a California company which specialized in the design and production of high reliability and low cost rocket engines.
The XR5M15 was one of XCOR's most powerful engine designs, with a rated thrust of 7500 lbf (33.4 kN).
This prototype engine was developed as a partnership between XCOR and ATK for NASA as part of the Vision for Space Exploration. It was intended to provide propulsion for return flights from the Moon and Mars, as well as for in-space maneuvering. The design built upon their smaller XR3M9 LOX/methane engine, and reused elements from many of their other designs.
As it is fueled by methane and LOX, this type of engine has a great deal of potential use for proposed Mars missions due to the possibility of producing methane on the Martian surface from locally available materials.