In the SpaceX Inspiration4 Launch broadcast at about T-01:31:05 (91 minutes before launch) the process for selection of launch windows for the mission is roughly outlined:

So the procedure for picking the launch window is actually a little bit different.

We reserved a couple of days -- a couple of twenty four hour days for the mission, but had to wait until L minus five, or five days before the first launch day that was selected to narrow it down to twelve hours. And then after that, we waited until L minus three to select the five hour window that we have today.

And then we have four opportunities in each of those launch windows about an hour apart, to lift off.

So it's a very unique case; so we really just knew just three days ago what the T zero in the launch window would be.

Question: Why are the four launch opportunities within each Inspiration4 launch window "about an hour apart"?

I don't know if it's relevant or not, but the orbital period of the final altitude of 575 km is about 96 minutes. I don't think it is relevant since there's no rendez-vous involved in this mission, but there could be an anti-rendez-vous; something at that altitude worth avoiding for example.

SpaceX Inspiration 4 Launch broadcast cued at about T-01:31:05 (91 minutes before launch) where the term "L minus five" is used:

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    $\begingroup$ A 5 hour window with 4 opportunities means they could actually be 96 minutes apart, matching the orbital period... just thinking... $\endgroup$
    – asdfex
    Commented Sep 16, 2021 at 14:06
  • $\begingroup$ It's possible they are talking about the recycle time. When they have a hold, they usually reset the clock to T-15 minutes, but I have never actually seen them pick the countdown back up. I would assume they need to defuel and refuel, and fueling starts at T-38 minutes. So, a couple of minutes for troubleshooting, 20 minutes for detanking, and then pick up the countdown at T-38 minutes would add up to "about an hour". This was a launch commentator making an unprepared remark, after all, not a PhD dissertation on orbital mechanics. $\endgroup$ Commented Sep 16, 2021 at 14:18
  • $\begingroup$ @JörgWMittag that's Jessie Anderson, a SpaceX Production and Engineering Manager What is it about her running commentary throughout that makes you feel she is "unprepared"? $\endgroup$
    – uhoh
    Commented Sep 16, 2021 at 14:22


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