Orbital Maneuvering System

The Orbital Maneuvering System (OMS) is a system of hypergolic liquid-propellant rocket engines used on the Space Shuttle and the Orion MPCV. 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. From STS-90 onwards the OMS were typically ignited part-way into the Shuttle's ascent for a few minutes to aid acceleration to orbital insertion. Notable exceptions were particularly high-altitude missions such as those supporting the Hubble Space Telescope (STS-31) or those with unusually heavy payloads such as Chandra (STS-93). An OMS dump burn also occurred on STS-51-F, as part of the Abort to Orbit procedure.

"Orbital Maneuvering System" redirects here, but can refer to any system used to modify a spacecraft's orbit. For the similarly-named Gemini component, see Orbit Attitude and Maneuvering System.

Space Shuttle OMS/RCS Pod
The underside of a left OMS/RCS pod on Space Shuttle Endeavour
ManufacturerAerojet
Country of originUnited States
Used onSpace Shuttle/Orion European Service Module
General characteristics
Length21.8 feet (6.6 m)
Width
  • 11.37 feet (3.47 m) (aft)
  • 8.14 feet (2.48 m) (forward)
Launch history
StatusPod Retired/Engines Active
Total launches135 Space Shuttle/ 1 Orion
Successes
(stage only)		134 Space Shuttle/ 1 Orion
Lower stage
failed		1 (STS-51-L)
First flightSTS-1 (12 April 1981)
Last flight
  • STS-135 (8 July 2011) for the Space Shuttle
  • Artemis 1 (16 November 2022) for the Orion
OMS Engine
Powered by1 AJ10-190
Maximum thrust26.7 kilonewtons (6,000 lbf)
Specific impulse316 seconds (vacuum)
Burn time
  • 15 hours (maximum service life)
  • 1250 seconds (deorbit burn)
  • 150–250 seconds (typical burn)
PropellantMMH/N
2O
4
Aft Primary RCS
Powered byPrimary RCS engines
Maximum thrust3.87 kilonewtons (870 lbf)
Burn time
  • 1–150 seconds (each burn)
  • 800 seconds (total)
PropellantMMH/N
2O
4
Aft Vernier RCS
Powered byVernier RCS engines
Maximum thrust106 newtons (24 lbf)
Burn time1–125 seconds (each burn)
PropellantMMH/N
2O
4

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, and the chamber pressure of the engine is 8.6 bar. The dry weight of each engine is 118kg (260lb). 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 MON-3 (mixed oxides of nitrogen, 3% nitric acid), 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 MON-3, allowing the OMS to produce a total delta-v of around 305 metres per second (1,000 ft/s) with a 29,000-kilogram (64,000 lb) payload.

  • Diagram of OMS pod components
  • An OMS pod detached from an orbiter for maintenance
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