I've watched a film where one of the characters claimed to have rapidly disembarked a moving spacecraft during a 5g burn (?!) and immediately wondered how he survived.

For example, you're on a spacecraft that's travelling at 100mph (or any other random speed) and you go to the nearest airlock and jump out (I.E: leave the spacecraft).

Assuming you have a strong enough protective suit (I.E: this isn't a murder/suicide):

  • What effect does this have on your body?
  • Does the vacuum of space mitigate or exacerbate the negative effects?
  • Will you just "float out" into space or will you actually be moving with/in the general direction of the spacecraft?
  • Do you slow down or speed up relative to the spacecraft?
  • How do the effects change as the speed changes?

I apologise for the multi-part question, but this question can't really be summarised in a single sentence.

UPDATE: Also, has this ever happened before? Has anyone ever "fallen out" of a spacecraft and made it back safely?

Thank you.

  • 2
    $\begingroup$ What's the difference between jumping out of the airlock and walking out into a vacuum on a scheduled spacewalk? $\endgroup$ May 29, 2020 at 20:37
  • 3
    $\begingroup$ There isn't any actual astronomy here, perhaps "physics" or "space exploration", I'd just note that space walks are routine from the space station, which is moving at about 7 km per second (ie a lot more than 100mph) relative to the Earth. Speed isn't a thing. It is only ever relative. The space station is motionless, relative to itself. $\endgroup$
    – James K
    May 29, 2020 at 21:56
  • $\begingroup$ I'm sceptical. Walking around in a spaceship that's doing a 5 g burn isn't exactly easy. You have 5 times your normal weight, and then there's the added weight of your spacesuit to consider. Unless you're really fit, just standing up at a "mere" 3 g is very hard work, even without a spacesuit weighing you down. This New Scientist article says "Five to 10 seconds at 4 to 5 g vertically typically leads to tunnel vision and then loss of consciousness." $\endgroup$
    – PM 2Ring
    May 29, 2020 at 22:48
  • 5
    $\begingroup$ I’m voting to close this question because it is not about Astronomy. However, it might be on-topic in Space Exploration SE $\endgroup$
    – uhoh
    May 30, 2020 at 5:28
  • 1
    $\begingroup$ This has now been posted in Space SE: What would happen if you jumped out of a moving spacecraft? $\endgroup$
    – uhoh
    May 31, 2020 at 1:59

1 Answer 1


If the spacecraft is not accelerating, the astronaut leaves the airlock and just floats outside, not moving relative to it. If the rocket is accelerating they "fall" down towards the stern from the perspective of people onboard; the astronaut would instead say the rocket is accelerating "upwards" and they are just floating.

In space, away from gravitational fields and in vacuum, only relative motion matters. You cannot tell whether the astronaut and spacecraft are moving at a high or low velocity compared to the rest of the universe just by looking at the two of them. So one can flip between the perspective that the craft is fixed and by turning on the engine it makes the astronaut (and everything in the craft) is accelerated, or the the perspective that the astronaut is floating in place and the rocket is speeding away. They are equivalent.

Astronauts leave spacecraft like the ISS all the time, and only experience free-fall despite the station moving at high speed around the Earth. As far as I know nobody has ever done a spacewalk when a craft is accelerating, for obvious safety and sanity reasons.

  • $\begingroup$ Thanks for taking the time to answer my question, I appreciate it. $\endgroup$
    – Malekai
    May 31, 2020 at 12:15

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