The Aerojet-built second-stage engine has been chosen by NASA to be used as the main propulsion engine for the Orion spacecraft that will replace the Space Shuttle after 2010. The engine was chosen due to its restart capabilites along with a switch from the original liquid oxygen/liquid methane (LOX/LCH4) application to hypergolic fuel and oxidizer similar to that in use on the Shuttle's OMS and RCS systems.