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, 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.
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.

The OMS consists of two pods mounted on the orbiter's aft fuselage, on either side of the vertical stabilizer.
Each pod contains a single AJ10-190 engine, based on the Apollo Service Module's Service Propulsion System engine, which produces 26.7 kilonewtons (6,000 lbf) of thrust with a specific impulse (Iₛₚ) of 316 seconds.
Each engine could be reused for 100 missions and was capable of a total of 1,000 starts and 15 hours of burn time.

These pods also contained the Orbiter's aft set of reaction control system (RCS) engines, and so were referred to as OMS/RCS pods.
The OM engine and RCS both burned monomethylhydrazine (MMH) as fuel, which was oxidized with dinitrogen tetroxide (N₂O₄), with the propellants being stored in tanks within the OMS/RCS pod, alongside other fuel and engine management systems.
When full, the pods together carried around 8,174 kilograms (18,021 lb) of MMH and 13,486 kilograms (29,732 lb) of N₂O₄, allowing the OMS to produce a total delta-v of around 1,000 feet per second (300 m/s) with a 65,000-pound (29,500 kg) payload.
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, 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. 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. 
The OMS consists of two pods mounted on the orbiter's aft fuselage, on either side of the vertical stabilizer. Each pod contains a single AJ10-190 engine, based on the Apollo Service Module's Service Propulsion System engine, which produces 26.7 kilonewtons (6,000 lbf) of thrust with a specific impulse (Iₛₚ) of 316 seconds. Each engine could be reused for 100 missions and was capable of a total of 1,000 starts and 15 hours of burn time.
These pods also contained the Orbiter's aft set of reaction control system (RCS) engines, and so were referred to as OMS/RCS pods. The OM engine and RCS both burned monomethylhydrazine (MMH) as fuel, which was oxidized with dinitrogen tetroxide (N₂O₄), with the propellants being stored in tanks within the OMS/RCS pod, alongside other fuel and engine management systems. When full, the pods together carried around 8,174 kilograms (18,021 lb) of MMH and 13,486 kilograms (29,732 lb) of N₂O₄, allowing the OMS to produce a total delta-v of around 1,000 feet per second (300 m/s) with a 65,000-pound (29,500 kg) payload.
Space Shuttle Orbital Maneuvering System