Orbital Maneuvering System

{{short description|Hypergolic orbital maneuvering engines used on NASA's Space Shuttle}}

{{Hatnote|"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.}}

{{Use dmy dates|date=January 2022}}

{{Infobox rocket stage

|image = OMS Pod removal.png

|imsize = 270px

|caption = The underside of a left OMS/RCS pod on Space Shuttle Endeavour

|name = Space Shuttle OMS/RCS Pod

|manufacturer = Aerojet

|country-origin = United States

|rockets = Space Shuttle/Orion European Service Module

|status = Pod: Retired
Engines: Active

|launches = Space Shuttle: 135
Orion: 1

|success = Space Shuttle: 134
Orion: 1

|noburn = 1 (STS-51-L)

|first = 12 April 1981 (STS-1)

|last = {{plainlist|

• Space Shuttle: 8 July 2011 (STS-135)
• Orion: 16 November 2022 (Artemis I)}}

|length = {{cvt|21.8|ft}}

|width = {{plainlist|

• {{cvt|11.37|ft}} (aft)
• {{cvt|8.14|ft}} (forward)}}

|stagedata =

{{Infobox rocket/Stage

|name = OMS Engine

|engines = 1 × AJ10-190

|thrust = {{cvt|26.7|kN}}

|SI = {{cvt|316|isp}}

|burntime = {{plainlist|

• 15 hours (maximum service life)
• 1,250 seconds (deorbit burn)
• 150–250 seconds (typical burn)}}

|fuel = MMH/MON-3

}}

{{Infobox rocket/Stage

|name = Aft Primary RCS

|engines = Primary RCS engines

|thrust = {{cvt|3.87|kN}}

|SI =

|burntime = {{plainlist|

• Up to 150 seconds (each burn)
• 800 seconds (total)}}

|fuel = MMH/MON-3

}}

{{Infobox rocket/Stage

|name = Aft Vernier RCS

|engines = Vernier RCS engines

|thrust = {{cvt|106|N|sigfig=2}}

|SI =

|burntime = Up to 125 seconds (each burn)

|fuel = MMH/MON-3

}}

}}

The Orbital Maneuvering System (OMS) is a system of hypergolic liquid-propellant rocket engines used on the Space Shuttle and the Orion spacecraft. Designed and manufactured in the United States by Aerojet,{{Cite journal|title=Capability and flight record of the versatile space shuttle OMS engine|journal=Space Technology and Science|author=D. Craig Judd|publisher=NASA|year=1992|page=107 |bibcode=1992spte.symp..107J}} 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.{{Cite web|url=http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-oms.html|archive-url=https://web.archive.org/web/20110629115908/http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-oms.html|archive-date=29 June 2011|title=Orbital Maneuvering System|publisher=NASA|year=1998}} 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.{{cite web|url=https://spaceflight.nasa.gov/outreach/SignificantIncidents/assets/space-shuttle-missions-summary.pdf|archive-url=https://web.archive.org/web/20170126160832/https://spaceflight.nasa.gov/outreach/SignificantIncidents/assets/space-shuttle-missions-summary.pdf|url-status=dead|archive-date=2017-01-26|title=Space Shuttle Missions Summary, NASA TM-2011-216142|author=Legler R. D. and Bennett F. V.|publisher=NASA|date=2011}}

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,{{cite report|title=Orbital Maneuvering System Design Evolution|first1=C. |last1=Gibson |first2=C. |last2=Humphrles|url=https://ntrs.nasa.gov/api/citations/19850008634/downloads/19850008634.pdf|publisher=NASA NTRS|access-date=December 6, 2022}} which produces {{Convert|26.7|kN}} of thrust with a specific impulse (I_sp) of 316 seconds.{{Cite web|url=http://www.astronautix.com/o/ome.html|archive-url=https://web.archive.org/web/20160827165114/http://www.astronautix.com/o/ome.html|url-status=dead|archive-date=27 August 2016|title=OME|access-date=16 September 2021|publisher=Encyclopedia Astronautica|year=2009|author=Encyclopedia Astronautica}} 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 {{convert|4087|kg}} of MMH and {{convert|6743|kg}} of MON-3, allowing the OMS to produce a total delta-v of around {{convert|305|m/s|ft/s}} with a {{convert|29000|kg|lb|adj=on}} payload.{{Cite web|url=http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/oms/storage.html|archive-url=https://web.archive.org/web/20010210010533/http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/oms/storage.html|url-status=dead|archive-date=10 February 2001|title=Propellant Storage and Distribution|access-date=8 February 2008|publisher=NASA|year=1998|author=NASA}}{{cite web|date=9 May 1997|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970509c.html|title=Spacecraft Fuel|publisher=NASA|author=David Palmer, Allie Cliffe and Tim Kallman}}

File:OMS Pod schematic.png|Diagram of OMS pod components

File:OMS pod.jpg|An OMS pod detached from an orbiter for maintenance