Soon the Inspiration 4 mission will launch and the crew will orbit the Earth for three days.
How will the crew capsule then deorbit? Will it use the super/regular Draco thrusters?
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1$\begingroup$ Related: space.stackexchange.com/questions/34699/… $\endgroup$– BowlOfRedSep 14, 2021 at 6:37
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Crew Dragon uses the regular Draco thrusters for the deorbit burn, and in fact for any burn during a regular flight. The Superdracos are only used for launch escape.
The main reason is that the Superdracos are too powerful. A deorbit burn with the Superdracos takes only a couple of seconds, which means that if they burn a little bit too long or too short, the deceleration is off by a significant fraction of the targeted Δ-v. A deorbit burn with the Dracos takes several minutes, which means an error of the same magnitude does not significantly alter the trajectory.
This means, however, that they need to commit to deorbit while the nose cone door is still open. In case they have trouble closing the nose cone door, they can't hang out in orbit and try to fix the problem. However, Dragon is designed to reenter with an open nose cone door (it will probably be ripped off by aerodynamic loads, also some sources say it can be explosively jettisoned), but it might have to be scrapped instead of reused afterward.
Interestingly, it seems this capability has never been tested, so either SpaceX and NASA are confident enough that the reentry with open nose works or confident enough that the nose can always be closed (or both).
answered Sep 13, 2021 at 15:47
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$\begingroup$ Unfortunately, I don't have any sources to offer. This was discussed on the livestreams for Demo-2 and Crew-1 return, but of course those are dozens of hours long … $\endgroup$ Sep 13, 2021 at 17:38
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$\begingroup$ Does Inspiration 4 have hatch under the glass? Because I highly doubt glass would survive reentry in case nose cone doesn't close. $\endgroup$ Sep 14, 2021 at 7:18
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$\begingroup$ I believe they only take out the docking adapter, the hatch stays in. But I don't think there have been official statements in this regard. Note that the nose is the leeward side of the vehicle on reentry. $\endgroup$ Sep 14, 2021 at 7:52