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The scenario: A Soyuz-MS spacecraft is on-orbit and ready for its deorbit burn. The crew then discover that there is a fault in the propulsion system and the deorbit engine can't fire. The craft is stable, in the correct orbit, and (apart from a non-functional engine) is fully intact. Is there any way the crew can return safely to Earth?

Nature of the failure (choose one):

  • Either the N2O4 or UDMH feedlines (you pick which) are fully blocked. Could the deorbit engine be used as a cold gas thruster? If so, would it have sufficient thrust?

  • Total failure of the N2O4/UDMH subsystem; it's intact but completely non-functional. Do the other thrusters (such as the H2O2 thrusters on descent module) have sufficient thrust to deorbit the craft? Are there any outside-of-the-box solutions?

Docking with a rescue vehicle/tug is specifically excluded.

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    $\begingroup$ On most craft the RCS can be used as a backup deorbit method. $\endgroup$ – Organic Marble Dec 26 '18 at 14:10
  • $\begingroup$ @OrganicMarble would that include the H2O2 thrusters on their own? I believe the primary RCS thrusters on MS are N2O4/UDMH based. $\endgroup$ – Alex Hajnal Dec 26 '18 at 14:13
  • $\begingroup$ No, the orbital RCS. $\endgroup$ – Organic Marble Dec 26 '18 at 14:13
  • $\begingroup$ The answer depends on the redundancy setup of the ship's prop system and exactly what you are failing. Not in a position to look into the former now. $\endgroup$ – Organic Marble Dec 26 '18 at 14:15
  • $\begingroup$ Right. It looks like there are RCS thrusters on the orbital module as well but it's not clear where they're tanked from. $\endgroup$ – Alex Hajnal Dec 26 '18 at 14:18

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