The Space Shuttle Orbital Maneuvering System (OMS) is a system of hypergolic liquid-propellant rocket engines used on the Space Shuttle. Designed and manufactured in the United States by Aerojet,[1] the system allowed the orbiter to perform various orbital maneuvers according to requirements of each mission profile: orbital injection after main engine cutoff, orbital corrections during flight, and the final deorbit burn for reentry.[2] Rarely the OMS were actually ignited part-way into the Shuttle's main ascent for a few minutes to aid acceleration to orbital insertion (usually while carrying heavy ISS payloads). This occurred on STS-128 and STS-135.