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Another question highlighted this SpaceX commentary for the GRACE-FO launch:

Now in order to fly an efficient trajectory for both of the payloads, we’re actually now running the second stage engine at lower power. That means the burn will be longer. For folks who used to seeing us shut down the upper stage engine nine to nine and a half minutes in to flight, today we’ll actually be shutting down the engine just past T+10 minutes into flight. As planned for today, the longer burn at lower power obviously takes more time, but gives us a more efficient trajectory.

The GRACE-FO orbit is comparatively low and circular. Entering it in the usual way, with a boost followed by a wait then a second circularization burn, would have put those two burns about 2 minutes apart. Instead, SpaceX used a longer single burn.

It could be that SpaceX wanted to avoid a "hot" restart of the engine. They routinely restart after the engine has had 20+ minutes to return to lower temperature. Has any mission had a restart after a shorter interval?

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    $\begingroup$ Didn't they do multiple restarts with the Falcon Heavy launch? $\endgroup$ – GdD May 29 '18 at 10:23
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    $\begingroup$ @GdD FH Demo has about 20 minutes between the first SECO and the restart, at the low end of the "pretty typical" range. spaceflight101.com/falcon-heavy-demo/flight-profile $\endgroup$ – Bob Jacobsen May 29 '18 at 14:28
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    $\begingroup$ is hot restart your own term? I haven't found references to specific issues, but maybe I'm looking in the wrong places. $\endgroup$ – GdD May 29 '18 at 15:18
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    $\begingroup$ I'm not sure "hot restart" is an official term, but it's pretty common when discussing smaller engines, i.e. dtic.mil/dtic/tr/fulltext/u2/a261774.pdf and more recently researchgate.net/publication/… $\endgroup$ – Bob Jacobsen May 29 '18 at 15:41
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    $\begingroup$ This seems like it should be doable, SpaceX usually publishes their timelines. $\endgroup$ – PearsonArtPhoto Mar 27 '19 at 13:22
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For the first launch of the ORBCOMM Gen 2 spacecraft there was exactly 1 minute between second engine cut off and second engine restart. Our satellite was deployed during this 1 minute window.

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  • $\begingroup$ just curious, is this the launch you're describing? And is it possible to find the time where the 2nd stage engine is restarted? youtu.be/O5bTbVbe4e4 and spacex.com/sites/spacex/files/… $\endgroup$ – uhoh Dec 12 '19 at 22:44
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    $\begingroup$ Actually the video you posted is for the first full stack of OG2 spacecraft. The timeline I referenced was for the pathfinder launch (spacecraft # 1 only as a secondary payload on an ISS cargo supply mission). The Dragon capsule was supposed to separate first, then, half an orbit later there was a second engine shutdown at T+54:11, OG2 separation, then second engine restart at T+55:11. Unfortunately, what really happened is the Falcon first stage blew an engine about a minute into ascent so we got dumped before Dragon instead :(. That ended in reentry after 3 days of struggle. $\endgroup$ – Terrance Yee Dec 13 '19 at 4:40
  • $\begingroup$ Ah that explains it, thanks! It might be a good idea to add that clarification back into your answer when you get a chance. $\endgroup$ – uhoh Dec 13 '19 at 5:20

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