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According to Wikipedia,

a launch window is the time period on a given day during which a particular rocket must be launched in order to reach its intended target.

SpaceX’s internet launch coverage stated there was a 20 minute “launch window” for Starship’ suborbital flight November 18 2023. What determined this launch window? There was no orbital rendezvous or sun-synchronous orbit to match. How can there be a launch window for a suborbital flight?

Was this a bureaucratic, rather than an orbital mechanics, launch window?

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    $\begingroup$ On the previous launch it was also noted that there once they had fully fueled with cryogenics that they had a limited window to either launch or start draining the tanks, so there may be additional no orbital dynamics related physical limits to a launch window. Comment not an answer since have not seen any similar commentary for November 2023 so possible design changes were made. $\endgroup$
    – GremlinWranger
    Nov 19 at 0:11
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    $\begingroup$ Friday's launch window was two hours. They postponed to Saturday because they needed to replace a grid fin actuator. The launch window for Saturday was twenty minutes which was likely related to the agencies that they were working with, as indicated in the answer by @DragonGeek. Orbital mechanics would not play a part for this test flight, although sometimes there are brief closeouts due to satellites that might be in the vicinity at a particular time. $\endgroup$
    – Steve Pemberton
    Nov 19 at 1:06
  • $\begingroup$ @GremlinWranger - that's a much bigger issue with Falcon 9 where they superchill the LOX just before loading, so they can only go a few minutes past the scheduled T-0. They don't use this method on Starship so they can go much longer once filled. I'm not sure how long but I think it's more than two hours. Friday's window was two hours so they can go at least that long. $\endgroup$
    – Steve Pemberton
    Nov 19 at 13:17
  • $\begingroup$ @StevePemberton As mentioned in a comment below, it's half an hour, not 2 hours. This was mentioned on SpaceX's live webcast. $\endgroup$
    – Steve Melnikoff
    Nov 19 at 21:28
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    $\begingroup$ @SteveMelnikoff - good to know, thanks. Since Starship fueling starts about 1 hour 40 minutes before launch, then probably the most likely reason to use up an entire two-hour window would be for weather. For example if the window is say 7:00 am - 9:00 am, and they start fueling at 5:20 am, they can launch between 7:00 and 7:30 am. But if the weather forecast is bad for 7:00 am but improving, they could start fueling at 6:50 am, then launch anytime between 8:30 and 9:00 am. $\endgroup$
    – Steve Pemberton
    Nov 20 at 0:05

3 Answers 3

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Besides the "physical" constraints of launch windows (orbital parameters, technical limits like fueling), keeping a launch window "open" is also associated with a large fiscal and organizational expense. There are many things that "need to happen" for a launch window to be realized, such as:

  • Road closures
  • NOTAM + Air traffic monitoring
  • Launch corridor ocean clearance
  • and more...

These are all not cheap, and it is directly possible to put a dollar-per-minute figure on them. For example, to ensure that the ocean is clear in the keep-out-zone, someone has to be paid to go out and actually do this. Communicate with traffic, utilize radar or similar systems to ensure it's clear, and if necessary, send coast guard military ships out to police the waves (the dollar-per-minute operating costs of military vessels are not cheap).

A similar situation is applicable with air traffic. The launch window and keep out zone needs to be communicated to all aviators and Air Traffic Controllers so that they can re-route aircraft out of this area. This, again, is connected to an actual financial cost. Airlines might incur financial damage by obeying a keep out zone (eg. they burn extra fuel) and someone has to communicate with all the ATC folks to make sure nothing goes wrong.

Even for the road closures point, some government or government-authorized official has to go out and put physical signs on the roads to stop traffic. In some cases, just like with air traffic, this disturbs commercial activity where shipping needs to re-route or delivery services suddenly can't reach their destinations.

The bottom line is that keeping a launch window open means imposing a small inconvenience on many people, and while a lot of this is covered under "good will" or "taxpayer dollars" along with the actual money that SpaceX pays for the launch licenses, the people calling the shots only have a certain tolerance limit.

I don't know specifically where the 20 minute launch window for Starship IFT2 came from, but it was not related to orbital mechanics or the technical limitations of the rocket and launch procedure. Therefore, yes, the launch window's shortness was administrative or bureaucratic in nature.

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    $\begingroup$ There's also the obvious fact that they use cryogenic propellant which won't stay cryogenic forever so they can't stay 2 weeks on the pad fully loaded they actually have a physical window due to propellant/oxydizer temperature $\endgroup$
    – Bakuriu
    Nov 19 at 10:33
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    $\begingroup$ @Bakuriu during the webcast, I think during the first 40-second hold, Innsprucker mentioned that the Starship stack has a 30 minutes where it can remain fueled and wait to launch. The 20 minute hold is stricter than the cryo limits $\endgroup$
    – Erin Anne
    Nov 19 at 20:27
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    $\begingroup$ @Dragongeek ... so your answer is "YES, it was an administrative launch window" ? $\endgroup$
    – Woody
    Nov 19 at 23:33
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    $\begingroup$ I believe in one of the previous launches one of the announcers mentioned that the fuel tank farm which fuels Starship contains about ~1.2 Starships worth of fuel. So they can accomodate some small delays and keep it topped off, but not indefinitely. Can't find the source for that, unfortunately. $\endgroup$
    – flibwib
    Nov 20 at 1:20
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    $\begingroup$ @Woody, I've amended my answer to make it more clear, but yes $\endgroup$
    – Dragongeek
    Nov 20 at 8:51
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To add to what Dragongeek said, there is a road in Boca Chica that must be closed for launches. So disruptive is this closure, that Elon Musk has considered building a tunnel near the launch site for the road

As SpaceX has ramped up Starship testing and launch activities in South Texas in recent years, the company has more frequently sought the closure of the Boca Chica Highway. This two-lane road runs along the company's rocket assembly and launch facilities.

Residents of South Texas use the highway primarily to travel from Brownsville and nearby towns to Boca Chica Beach, the southernmost beach in Texas. When the road is closed, no one can access or remain on the beach.

And

SpaceX founder Elon Musk has a potential solution. The Brownsville Herald reports that officials from Musk's The Boring Company met with Cameron County officials in July to discuss digging a tunnel from the south end of South Padre Island to the north end of Boca Chica Beach, facilitating alternate access to the barrier island.

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In the latest episode of What about it!?, the host claimed that a cruise ship was scheduled to enter the area (presumable to dock in the Port of Brownsville) later in the day, and that this was the reason for the short launch window:

However, there are no sources cited in the video.

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  • $\begingroup$ In January 2022 a cruise ship leaving Port Canaveral caused a scrub of a Falcon 9 carrying an Italian satellite. An article about the investigation mentions changes made as a result. An interesting comment in the article possibly related to your answer was, "The changes include updated exclusion zones and new modern ways of disseminating launch updates to ship captains. The new rules also consider the possible delays a rocket launch could have on cruise ships." $\endgroup$
    – Steve Pemberton
    Nov 21 at 23:57

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