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ISRO expressed concerns on restarting the Liquid Apogee Motor (LAM) for Mars Orbit Insertion (MOI) after a long coasting period of its Mars Orbiter Mission (MOM). ISRO has redesigned the LAM plumbing to isolate the fuel / oxidizer lines used for Trans-Mars Injection (TMI) and instead use separate (and fresh) fuel / oxidizer lines for the MOI manoeuvre.

ISRO will test fire the LAM ahead of MOI for a short duration to check its health. Plan B, if it does not pass the test, is to use the attitude thrusters for MOI to enter a mission salvaging orbit around Mars.

Both the LAM and the attitude thrusters use the same fuel/oxidizer from shared tanks:

http://www.isro.org/mars/pdf/press%20briefing%20on%20MOI.pdf (page:8)

How is it then, that the thrusters are considered more reliable than the LAM?

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It's not clear that the thrusters are considered more reliable. It may be as simple as it being unlikely that both the LAM and the thrusters would fail, and the thrusters have quite a bit of redundancy if a subset fail. Depending on how they're arranged, four working thrusters might be enough to orient the craft for the MOI burn, and two could do the "Plan B" burn.

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  • $\begingroup$ A relatively shorter down-time on the thrusters too. They were used as recently as June 2014, and another burn was scheduled for September 14th which was re-scheduled to occur September 22d (isro.org/mars/pdf/press%20briefing%20on%20MOI.pdf) The fuel system diagram on page 8 of that document may be helpful for anybody who knows how to interpret it (+: I don't $\endgroup$
    – Everyone
    Sep 17, 2014 at 2:57

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