Can the space shuttle use its OMS engines if the shuttle is short during the runway approach? Is fuel available for use in such a situation and will the engines provide reasonable thrust to get to the runway?

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    $\begingroup$ I would be surprised if they wouldn't immediately destroy themselves because of flow separation. They are vacuum engines, after all, not sea-level. The OMS engines for Orion (which are refurbished Shuttle OMS engines) are test-fired in a vacuum chamber. SpaceX recently tested a vacuum version of the Raptor at sea-level ambient pressure, but they had to run it at full throttle, and add additional bracing to the nozzle, to prevent it from destroying itself. $\endgroup$ Commented Jan 24, 2021 at 7:54
  • $\begingroup$ This spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/oms/… indicates 70k feet as lowest altitude to operate the OMS but not what physics that comes from. $\endgroup$ Commented Jan 24, 2021 at 9:25
  • $\begingroup$ @GremlinWrangler it's because the engine bells would collapse due to the low pressure inside / high pressure outside. That is indeed the answer. $\endgroup$ Commented Jan 24, 2021 at 12:57
  • $\begingroup$ I would expect this to work like "base bleed" in artillery shells. The exhaust wouldn't need to produce trust so much as reduce the wake drag. $\endgroup$
    – MSalters
    Commented Jan 25, 2021 at 12:03

1 Answer 1



As mentioned by @GremlinWrangler in a comment, the Orbital Maneuvering System (OMS) engines could not be fired below 70,000 ft (21 km) altitude.

The minimum altitude for an OMS engine burn is 70,000 feet. Below this altitude, the pressure difference between the inside and the outside of the OMS engine nozzle could cause it to collapse.

Source: Orbital Maneuvering System training manual, p. 3-18


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