If there was an urgent need to launch a rocket to the ISS, how long would it take to have a rocket ready to launch?

I am trying to understand what factors take up the time to prepare for a rocket launch.


Here are some clarifications to limit scope. I am curious how long it takes to prep an emergency launch from a rocketry perspective.

  • Assume there was an urgent need to deliver a small, lightweight package with something vital such as medicine or a replacement circuit board that is available.

  • Assume we CAN use an existing rocket.

  • Assume the rocket is NOT sitting ready on a launchpad.

  • Assume travel to the ISS is within the capabilities of the rocket.

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    $\begingroup$ What are you sending to the ISS? Cargo? Human passengers? Empty seats? $\endgroup$
    – Dragongeek
    Commented Feb 26, 2020 at 19:59
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    $\begingroup$ @Dragongeek: good questions. It is just a hypothetical example that eliminates schedule backlog. Schedule is real, but transcends rocketry. Assume the needed cargo was small and ready to go. If we were able to bump a rocket to the front of the schedule. How long would it take to prepare for a launch as far as rocketry is concerned? Are we talking months, weeks, days, hours? $\endgroup$ Commented Feb 26, 2020 at 20:17
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    $\begingroup$ I picked the ISS example as it's a known, regular mission. Nothing exotic. I am curious if the long times between launches are related to particular needs of rocketry or outside factors such as waiting on completion of a payload. $\endgroup$ Commented Feb 26, 2020 at 20:22
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    $\begingroup$ @uhoh no problem! I'm still confused. $\endgroup$ Commented Feb 27, 2020 at 1:32
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    $\begingroup$ I would exclude "medicine" from the list of emergency supplies. If someone on the ISS is that urgently in need of something medicinal, it's more likely the crew would leave the station and return to Earth than wait for medicinal supplies to be brought up to them. That can be done in a matter of hours rather than weeks. $\endgroup$ Commented Feb 27, 2020 at 14:47

5 Answers 5


A brand new rocket to be launched will have to be assembled, and that's a long process, though I do not know how long.

But if it's for an emergency, you may find ready rockets.

After the Columbia disaster, space shuttle missions all had a contingency mission in case they found issues with the orbiter before reentry.

The planning and training processes for a rescue flight would allow NASA to launch the mission within a period of 40 days of its being called up. During that time the damaged (or disabled) shuttle's crew would have to take refuge on the International Space Station.

You even had two shuttles on pad at the same time for a Hubble servicing mission, as the crew wouldn't be able to reach the space station for a safe haven, and would need to be rescued before the three weeks of consumables on board were exhausted.
The rescue mission would have been launched only three days after call-up.

Space shuttles Atlantis and Endeavour on launch pads

That said the space shuttle isn't operating anymore, and until Spacex' Crew Dragon or Boeing's Starliner are operational (probably sometime soon), the Russian Soyuz is the only option to send people, and it seems to launch a new crew to the ISS roughly every 6 months (if there are no emergencies).
For the last flight of the space shuttle, there was no contingency mission prepared, but instead the mission had only 4 astronauts, and in the case that Atlantis couldn't make the reentry, the astronauts would stay on board the ISS and come back to earth in Soyuz capsules over the following year.

If your emergency doesn't require people to go to the ISS to help, but specific, unplanned cargo is still needed, a spacecraft (cargo or not) goes to the ISS every month or so, so if your emergency can wait between a week and a bit more than a month or so (to account for weather delays, mounting time of the payload and orbit maneuvers) you can just sneak it in one of those resupply missions, or replace some less vital cargo.

If your emergency can't wait at all, and you absolutely need to send something to the ISS on short notice, and there are no upcoming resupply missions, you may be able to hijack another vehicle with sufficient authority.
For March alone there are 10 planned rocket launches from the US, ESA or Roscosmos, so you could probably get emergency cargo to the ISS in around a bit more than a week (this is a guess, assuming the orbital maneuvers take around 3 days, and mounting the payload and waiting for a launch window take a few days too).
Note that if you don't have a proper cargo spacecraft to put the cargo into, maneuvering up to the ISS might prove to be difficult, and the cargo will not be able to mate with the ISS, so astronauts may have to perform an EVA to secure the cargo outside.

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    $\begingroup$ That is some fantastic information! I did not know about the shuttle contingencies post Columbia. Seems your answer boils down to it being faster to wait for a planned mission than to re-purpose a rocket for an emergency if one arose. $\endgroup$ Commented Feb 27, 2020 at 0:28
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    $\begingroup$ @DanSorensen Yes but a lot of what I put in my answer is guesswork and extrapolation from that link on the launch schedule. There might exist some rockets ready at all times, maybe initially meant to carry small payloads or satellites $\endgroup$ Commented Feb 27, 2020 at 0:35
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    $\begingroup$ What a great photo... $\endgroup$
    – T.J.L.
    Commented Feb 27, 2020 at 15:56
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    $\begingroup$ From launch to ISS has been done in 4 hours nasaspaceflight.com/2018/07/… so your 3 days of orbital manoeuvrers would seem to be a bit high for an emergency mission. Obviously, the launch window was carefully chosen to minimise the mission duration. Edit: The article states missing the window "would have resulted in the craft having to fly a two-day [...] phasing profile to the ISS on a realigned launch date later this week" so I guess less than a week to launch, with a two day intercept? $\endgroup$
    – Baldrickk
    Commented Feb 27, 2020 at 16:53
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    $\begingroup$ So, it's basically risk management. "We have a launch scheduled to depart in two weeks. We could launch it in one week instead, but it will have a much higher chance to explode, and then we have to wait months for the next one. Do we want to risk it?" $\endgroup$
    – vsz
    Commented Feb 28, 2020 at 5:06

The ISS does not have emergency's that require a rocket to bring supplies. It can have an urgent need of something. Either everyone stays on the ISS or some/all crew leave. It is downhill all the way to Earth, and the crew can leave anytime. Worst case the crew abandons the ISS and it burns up on re-entry.

There are a couple of good answers on this question, that talk about some of the challenges. But in the end the answer is "It depends, how much do you want to spend?"

There are also a couple of good posts that talk about real emergencies.

Would all crew leave the ISS if one had a medical emergency?

How long can a 2 person crew survive on ISS totally cut from Earth?

  • $\begingroup$ Would the ISS actually burn up completely? It's pretty big. $\endgroup$ Commented Feb 28, 2020 at 2:35
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    $\begingroup$ @FabianRöling No, the Mir was much smaller and about 40 tons of debris ended up in the seas somewhere when it was decommissioned. $\endgroup$
    – smcs
    Commented Feb 28, 2020 at 10:33
  • $\begingroup$ "It is downhill all the way to Earth, and the crew can leave anytime." Can you please clarify this? Can they all leave AND survive? $\endgroup$ Commented Feb 28, 2020 at 12:32
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    $\begingroup$ @TomášZato-ReinstateMonica read the Q&A "Would all crew leave the ISS if one had a medical emergency?" I linked in my answer. It should answer your question, and give you more detail. $\endgroup$ Commented Feb 28, 2020 at 14:30
  • $\begingroup$ New related question based on first two comments What parts of the ISS would impact the Earth with potentially harmful energy? $\endgroup$ Commented Feb 28, 2020 at 16:53

It depends on readiness of a rocket. Rocket assembly is rather long process. If you compare the dates of rocket delivery to launch facility and the launch you'll find that usually it takes about month or more.

So if some rocket is ready to launch to ISS in coming days it's rather easy - just throw out some of less significant things and replace it by the emergency cargo. Well, maybe the cargo should be qualified for spaceflight (e.g. toxicity, srtength for 5-g accelerations, weightlessness behaviour, radiofrequency interference, etc), but for high emergency some of qualifications could be lifted, I think.

But if no any rocket is planned to launch to ISS in next month or two - there is a big problem, and I would say it'll be close to impossible to accelerate the launch so much. Most of the time is spent on tests and checks of rocket and launchpad, so theoretically most of them could be skipped, but... List of rocket disasters tells us why the checks are so rigorous. Also, modern rockets (Falcon, Atlas V, Soyuz-2, H-IIB) make automatic self-checks before launch, and the countdown will be stopped by the rocket itself if something wrong found. Maybe the self-checks can be swithed off, too, but it's already a management nightmare without guarantee of success. All the lauch personnel was teached to follow the rules, and now they should skip most of them but make the thing flying...

It's hard for me to imagine a scenario where emergency delivery to ISS can't wait at least a month. ISS have a lot of spares for this case. The crew can be evacuated if they can't stay. So the danger should be for the whole of ISS structure. Maybe some thermal regulation problem that can result in major overheat or freezing, so most of the equipment and interiors will be irreparable. In such improbable case the risky launch acceleration can be justified - try to fly now or there'll be nothing to save.

Disclaimer: I'm not a space technology specialist, so take my post with grain of salt.


NASA has priority over almost any customer from SpaceX, so if a Dragon capsule was available, it could be done on short notice. Assuming that it would be something that fits in to a dragon capsule, it could potentially be done in a matter of a few weeks. If the hardware isn't available, it would be a few months.

But realistically, this isn't very likely to happen. If there was an emergency on the ISS, the astronauts would go home.

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    $\begingroup$ Source for "NASA has priority over almost any customer from SpaceX" ? What is the customer with higher priority that justifies the "almost"? $\endgroup$ Commented Feb 27, 2020 at 18:37
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    $\begingroup$ @OrganicMarble Isn't DOD a customer? $\endgroup$ Commented Feb 27, 2020 at 18:57
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    $\begingroup$ I do know that the Zuma launch actually bumped a NASA launch. I think in an emergency NASA would probably be a priority, but that is the justification for the statement. space.stackexchange.com/a/23722/25 $\endgroup$
    – PearsonArtPhoto
    Commented Feb 27, 2020 at 22:05
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    $\begingroup$ @PearsonArtPhoto: thank you for the rough time frame. That answers my question. I realize it isn't likely to happen -- but that time frame (and the cost behind it) is the real reason why it can't happen. Appreciate it. $\endgroup$ Commented Feb 27, 2020 at 22:09

Considering spacex is now launching every week with several stage1’s ready to go (on pre launch preps and fuelling needed) i would say they can interchange the stage 2 with dragon capsule and run all the checks in a day or two. Since its an emergency, there will be nothing holding them off like air-traffic, permit and other documentation so basically they can do it in 2days(my guess) again considering they are launching every week now.

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    $\begingroup$ While probably reasonable there are a lot if 'guess' in this answer. It would be good to chase down for example how many dragon capsules exist and any information on the non re- usable parts being made (trunks?). The rest probably propriety unfortunately. $\endgroup$ Commented Apr 20, 2023 at 11:31
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    $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Commented Apr 20, 2023 at 12:47
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    $\begingroup$ Better to post supported answers than guesses. $\endgroup$ Commented Apr 20, 2023 at 13:21

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