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The Crew dragon launches with a fairly large amount of fuel for its SuperDraco thrusters so that they can provide launch escape. If the launch goes OK is that fuel carried all the way to orbit and back or is it vented at some point?

If it is carried, why? Surely it could be dumped once launch escape is no longer needed (after first stage separation?) increasing usable mass to orbit? Or dumped in orbit to increase the payload that can be brought back?

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    $\begingroup$ My assumption (if it's carried) is that the firing or venting of the fuel has more risk to the mission than keeping it onboard. Also, having fuel as opposed to not having fuel may open up additional abort contingency possibilities. $\endgroup$
    – CourageousPotato
    Aug 2, 2020 at 23:23
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    $\begingroup$ Note well: The Space Shuttle dumped any remaining main engine propellant early on during reentry, leaving only the hydrazine needed to power the auxiliary power units (APUs) that powered the Shuttle's hydraulic pumps that in turn drove the Shuttle's aerodynamic effectors. $\endgroup$
    – David Hammen
    Aug 3, 2020 at 4:11
  • $\begingroup$ Nope, all main engine prop was dumped and inerted shortly after MECO. You might be thinking of the dump of the forward reaction control system prop right before entry. The aft RCS was active during entry; the yaw jets fired until quite a low altitude. $\endgroup$
    – Organic Marble
    Aug 4, 2020 at 3:24

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Yes, fuel is still carried. Only 600 m before splashdown (2:12 in this video), "Dragon has safed all propulsion systems on board." https://www.space.com/spacex-crew-dragon-demo-2-splashdown.html
So propulsion must be useful in some contingency even that close to splashdown. But I won't speculate on what contingencies were considered.

Edit: On 2019 March 19 Elon Musk said that the thrusters are "likely" a backup for if the chutes fail.

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    $\begingroup$ It's polite when a downvoter adds a comment. This answer provides a citation, and admits that the answer is not complete. $\endgroup$
    – David Hammen
    Aug 3, 2020 at 3:38
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    $\begingroup$ Alternatively, venting any remaining propellant that close to the ground might well be viewed as a greater vehicular hazard than simply leaving the propellant on-board, or might be viewed as an environmental hazard as both nitrogen tetroxide and hydrazine are highly toxic. $\endgroup$
    – David Hammen
    Aug 3, 2020 at 3:59
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    $\begingroup$ BTW, I am not the downvoter. This is a much better answer than is the other answer as of the time of this comment. $\endgroup$
    – David Hammen
    Aug 3, 2020 at 4:26
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    $\begingroup$ It isn't clear to me, at least from this quote from the video whether anything like the full load of fuel that would be needed for launch abort (a few hundred kilos at least) is still present, or if the safing relates to much smaller amounts for attitude control or even just to residue in tanks or pipework. $\endgroup$
    – Steve Linton
    Aug 4, 2020 at 9:42
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Yes, the fuel for the launch abort system is kept during the duration of the flight, however it is not wasted.

The SuperDraco abort thrusters use the same combination of propellants (NTO and N2O2) that the Draco maneuvering thrusters use. In fact, they use the same propellant storage tanks, with different pressurization lines and fuel valve systems.

Dumping the fuel during ascent or on-orbit is not necessary, since it can be used to provide an additional margin for orbit maneuvering.

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  • $\begingroup$ Citation needed. $\endgroup$
    – David Hammen
    Aug 3, 2020 at 3:38
  • $\begingroup$ The question isn't whether dumping propellant during ascent or on-orbit is necessary. The question is why the propellant isn't dumped at some point during reentry. In particular, does the Dragon use any propellant after parachutes have been deployed, and if not, why isn't the propellant dumped shortly after parachute deployment? $\endgroup$
    – David Hammen
    Aug 3, 2020 at 4:14
  • $\begingroup$ How much fuel is used in the long de-orbit burn -- is that significant fraction of the load? $\endgroup$
    – Steve Linton
    Aug 3, 2020 at 15:36
  • $\begingroup$ They carry a significant mass of fuel (500 kg+ I think) for launch escape. That's a lot to haul up to orbit just for "additional margin". $\endgroup$
    – Steve Linton
    Aug 4, 2020 at 9:44

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