XCOR and ATK developed this prototype LOX/methane rocket engine as a stepping stone to NASA's original Orion CEV manned spacecraft and return to the moon and manned mission to Mars plans. These envisioned a shift to methane propulsion, since methane could be extracted from the Martian atmosphere. The 5M15 was based on XCOR's existing 3M9 LOX/methane engine, as well as the 8 kN 4K5, 22.3 kN 5M12 design, and 1.78 kN 4A3 engines.
The planned CEV main engine development used several features from the 3M9, including the augmented torch electrical ignition system and propellant combination. Relevant features taken from the 4K5 engine included the igniter geometry, the torch spark igniter, and the fuel cooling configuration. However compared to the 4K5, the 5M15 used a different fuel, a lower chamber pressure, and was larger. 3M15 design used methane cooling analysis tools developed for the XR5M12 DARPA concept engine, and proven in 3M9 engine runs. Many 5M15 engine features were proven in XCOR's FAA licensed manned vehicle, the EZ-Rocket.
The prototype engine validated key engine design elements, including the regeneratively cooled chamber/throat assembly, the stability and performance of the injector, and the reliability of ignition. It also incorporated safety and reliability features needed for the CEV human-rated application. The modular design facilitated rapid test of new components during development, and enabled modification of the design to a space-weight version for future exploration applications
Application: First stages.
Thrust: 33.36 kN (7,500 lbf).
First Launch: 2006-2008.