In media you’ll occasionally see someone stranded in freefall in space use a gun, or fire extinguisher, or thrown object, or something to try to alter their trajectory. Hell, pop a bottle of champagne and rechristen the ship!
Would this actually work though? I know you don’t have to deal with friction, but would these tiny amounts of thrust be enough to significantly effect a much more massive object?
Will firing a 125 gram 9mm round have a noticeable effect on a 80,000 gram astronaut drifting away from his ship?
It seems hard to believe,but then I’ve heard of stuff like solar sails which can apparently move an entire ship using just photons? So I don’t know.
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The momentum of a 20 gram bullet fired from a gun is roughly 10 kg m/s. What that means is that, if a 10 kg object had that momentum, it would be going at one meter per second (roughly walking speed). Assuming that our astronaut and all their equipment were 200 kg, the speed would go down to 0.05 m/s. So the recoil from the gun would get them moving, but they’d be going at a snail’s pace. So long as the need to get somewhere isn’t urgent, they’ll get there. Something with more continuous thrust like your fire extinguisher would work better since it would work more like a rocket.
Of course, the big problem is making sure that the impulse that gets the astronaut moving is properly centered. If they’re holding the gun from their centre of mass, they’ll be fine. If they’re holding it like they would on Earth though, they’d be sent spinning head over heels instead of heading toward their destination. On Earth, people trained to use guns brace themselves against the ground so the recoil doesn’t knock them over. In space, there’s no ground to brace against.
If you’ve seen The Martian, there’s a scene in the climax where Watney gets into space but is just barely too far away from Hermes to reach safety. So he cuts a hole in the palms of his spacesuit so that he Iron Mans the rest of the way. In the original book, the crew shoot down that idea the moment he suggests it, not because he couldn’t achieve enough thrust but because he wouldn’t be able to modulate his angular momentum to avoid spinning around in a circle.
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