[2] 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).

[3] The OMS consists of two pods mounted on the orbiter's aft fuselage, on either side of the vertical stabilizer.

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.

[8] It would have used one, two or three sets of OMS tanks, installed in the payload bay, to provide an extra 150 m/s, 300 m/s or 450 m/s( (500 ft, 1000 ft/s or 1500 ft/s) of delta-V to the orbiter.