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-51-F, STS-124, STS-128 and STS-135.
|Country of origin||United States|
|Used on||Space Shuttle|
|Length||21.8 feet (6.6 m)|
|First flight||STS-1 (12 April 1981)|
|Last flight||STS-135 (8 July 2011)|
|Powered by||1 AJ10-190|
|Maximum thrust||26.7 kilonewtons (6,000 lbf)|
|Specific impulse||316 seconds (vacuum)|
|Aft Primary RCS|
|Powered by||Primary RCS engines|
|Maximum thrust||3.87 kilonewtons (870 lbf)|
|Aft Vernier RCS|
|Powered by||Vernier RCS engines|
|Maximum thrust||106 newtons (24 lbf)|
|Burn time||1–125 seconds (each burn)|
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. The oxidizer-to-fuel ratio is 1.65-to-1, The expansion ratio of the nozzle exit to the throat is 55-to-1, The chamber pressure of the engine is 8.6 bar. The dry weight of each engine is 260 pounds. 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 (N
4), 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 4,087 kilograms (9,010 lb) of MMH and 6,743 kilograms (14,866 lb) of N
4, allowing the OMS to produce a total delta-v of around 1,000 feet per second (300 m/s) with a 65,000-pound (29,000 kg) payload.
Diagram of OMS pod components
An OMS pod detached from an orbiter for maintenance
It was never built, but to augment the OMS an OMS Payload Bay Kit was proposed. It would have used one, two or three sets of OMS tanks, installed in the payload bay, to provide an extra 500 ft/s, 1000 ft/s or 1500 ft/s of delta-V to the orbiter. The orbiter control panels had related switches and gauges but they were nonfunctional.: 1–2
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