Space Shuttle OMS Engines
Aerojet Rocketdyne produced the Orbital Maneuvering Subsystem engines for the space shuttle. The engine is a pressure-fed, multiple-restart reusable engine that performed orbit insertion and circularization, maneuvering, and braking for each shuttle mission. The rated thrust for each engine assembly is 6,000 lbs (vacuum) and the expansion ration is 55:1. These engines use N2O4 and MMH propellants and were rated for 100 missions. The OMS engines consistently performed to all original specification since the first shuttle flight in 1981 until the final flight in July 2011. The OMS have exhibited the highest reliability of any operational reusable engine (zero failures).