Microcosm was developing a family of liquid-propellant rocket engines for its Scorpius series of ELVs and other users. The company has built a pressure-fed, ablatively cooled, 22,250-newton thrust engine using liquid oxygen and jet fuel as propellants. This engine was successfully tested on the company's SR-S and SRXM-1 sounding rockets launched in January 1999 and March 2001. The engine would also be used as the upper stage engine for the Sprite Mini-Lift orbital vehicle should that vehicle move into final development.