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Organic Marble's answer to STS: How much thrust did the nominal post-MECO LOX dump produce? explains that the LOX dump was only started two minutes after MECO, while it was also desirable to finish the dump as soon as possible to enable shutting down the APUs. Two minutes is quite a lot of time in the context of a rocket launch, and a SSME becomes completely useless the moment it shuts down as it can't be reignited, so there's no point keeping the engine "armed".

What was the main factor determining the required length of the delay? (Corrosion of hot engine parts by the LOX dump? Temperature shocks? Venting of residual LH2 first? Something completely different?)

TooTea
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  • Posting as a comment because I don't believe it's explicitly written down anywhere, but I'm pretty sure it was because 1) some stuff happens in there that the crew needs to monitor (ET sep for one) 2) Some time is needed to "catch up" after MECO, check that the MECO targets were met & whether OMS 1 is required, see if malfunctions that occurred during ascent need to be followed up, get with the ground on all this, etc. etc. I'll continue to look for a reference. – Organic Marble Jan 17 '24 at 22:44

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