[basing this question on the Falcon 9, Paz satellite launch on 22 Feb]

Hi, this is probably a silly question, but there is an approx 3 minute time difference between second stage engine cutoff and the payload deployment stage. Why is this needed?

  • 3
    $\begingroup$ Related, if not a duplicate: Why is there a “coasting” phase in some space launches? $\endgroup$ – David Hammen Feb 27 '18 at 19:43
  • $\begingroup$ possibly to check the achieved orbit and attitude; ensure there is no residual thrust; or to prepare hand-over of control from launch to operational teams. $\endgroup$ – user20636 Feb 28 '18 at 4:41
  • $\begingroup$ Perhaps a better phrasing of this interesting question might be "Why was the coasting phase of the Falcon 9, Paz satellite launch only 3 minutes long?" or something similar? $\endgroup$ – uhoh Feb 28 '18 at 6:13
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    $\begingroup$ Possible duplicate of Why is there a "coasting" phase in some space launches? $\endgroup$ – Martin Schröder Feb 28 '18 at 15:43
  • $\begingroup$ This isn't a duplicate, as it's asking about the coast between the final cutoff of the engine and satellite deployment. The other question is above coast earlier in the launch sequence. $\endgroup$ – Bob Jacobsen Mar 30 '18 at 16:34

Three things happen in sequence at the end of the final burn:

  • Check the orbit, which involves some measurement time to get doppler and/or radar readings
  • Set the spacecraft attitude so it's pointing in the right direction for release (as opposed to the right direction for thrust)
  • Do the pre-release operations on the satellites

What's needed in pre-release varies. You want the satellites attitude control to be working when you release it, but there are some things (opening pre-valves, etc) that you don't want to do while the satellite is under acceleration. But generally, this entire sequence is just a couple minutes of work.


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