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?

NOTE: I've asked this question over on the Astronomy StackExchange and was told that it might be a better fit here, if cross-posting isn't allowed on this StackExchange give me a heads up and I'll delete it.

Thank you.

  • $\begingroup$ Related: space.stackexchange.com/questions/17739/… $\endgroup$ May 30, 2020 at 13:55
  • $\begingroup$ I think you'll get more response here for sure! Your question in Astronomy is nearly closed so it cant receive further answers, but now that there is one answer you can't delete it yourself there. Ideally you should have just waited longer and after it was closed a moderator could have started migrating it to here. $\endgroup$
    – uhoh
    May 30, 2020 at 14:23
  • $\begingroup$ There will be a big difference between jumping out during a "5G burn" and jumping out when no burn is taking place. $\endgroup$
    – aranedain
    May 30, 2020 at 15:29
  • $\begingroup$ "Jumping out pf the spacecraft" is exactly equivalent to "letting go of all parts of the spacecraft while remaining inside" . if you ignore air friction... $\endgroup$
    – DJohnM
    May 30, 2020 at 16:51

1 Answer 1


If your vehicle is in space (not in an atmosphere or supported by ground), the only forces acting on the vehicle (and you as an occupant) come from thrust applied by the vehicle's engine(s). If no thrust is being applied to an object in space, it will feel no acceleration; it might be accelerating due to gravity of a planet, star, or other object, but it will not be "felt" because there is nothing to oppose it such as when you are standing on solid ground.

If a spacecraft is executing a 5G burn, all objects inside it will feel the 5Gs, including you, as an occupant. You might find it difficult to exit the vehicle because you would feel yourself and your spacesuit having 5 times its "normal" weight. 5G would be enough to pretty much pin you to the floor, your seat, or whatever. However, if you did depart your spacecraft while it was executing a 5G acceleration, the instant you were no longer in physical contact with it, there would be nothing to keep you accelerating along with it and your acceleration would immediately cease; you will see the spacecraft accelerate away from you at 5G, rapidly leaving you far behind. Consider what would happen if you pushed some object off the edge of a table... when it is no longer supported by the table, it accelerates at 1G until it strikes the floor (ignoring air resistance for the sake of simplicity here). This is comparable to you departing an accelerating spaceship because its acceleration mimics the effect of gravity (or vice-versa) and free-fall or free-floating in space are equivalent states.

For this thought experiment, speed is irrelevant; only forces and accelerations are meaningful.

Once you have departed your spacecraft, the only way to get back is to apply enough thrust to exceed its acceleration so that you can catch up, or for it to come back to get you.

  • $\begingroup$ I think your last sentence has an interesting implication. In orbit around Earth (for example), the floating astronaut and spacecraft would share roughly the same perigee, but would be phased differently right? Also, would it really be as simple as exceeding the spacecraft's thrust along the same vector (or vice versa, the spacecraft does a retrograde burn)? $\endgroup$
    – aranedain
    May 30, 2020 at 16:33
  • $\begingroup$ "f your vehicle is in space (not in an atmosphere or supported by ground), the only forces acting on the vehicle (and you as an occupant) come from thrust applied by the vehicle's engine(s)" Gravity is acting on both. $\endgroup$ May 30, 2020 at 16:42
  • 1
    $\begingroup$ @aranedain Strictly speaking, if your spacecraft was in an orbit (say, around Earth) and began a 5G acceleration, in a manner of speaking, it would no longer be in an orbit, at least not while it is applying thrust. Throughout the burn, its orbital parameters will be continuously changing until the burn ceases; its final orbital parameters would depend on its position and velocity vector once thrust became zero. For an astronaut "left behind" to successfully rendezvous, the required maneuver would be a bit more complicated than simply replicating the maneuver executed by the spacecraft. $\endgroup$
    – Anthony X
    May 30, 2020 at 16:44
  • $\begingroup$ Also, since if the spacecraft is under extreme acceleration, it's likely burning very hard. Anyone, even in a suit, would probably be killed instantly when they pass the engines. $\endgroup$
    – Dragongeek
    May 30, 2020 at 17:45
  • $\begingroup$ @Dragongeek yes, and said astronaut would be pushed onto who-knows-what trajectory by the exhaust, not simply backwards because it would depend on the locations/orientations of the surfaces on which the exhaust impinges. $\endgroup$
    – Anthony X
    May 30, 2020 at 18:08

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