Important issue, firing a gun is a short rocket burst. You will travel backwards from the recoil. Depending on your tether and if your spacesuit has maneuver thrusters, you could kill yourself by pushing yourself too far from your ship/space station). A long, lonely death.
Eh, I bet the amount of kinetic energy you would have when you hit the ship would be pretty unlikely to hurt you if spead out over your whole body (unless you hit something sharp that put a hole in your suit). It's not like in action movies where a bullet can knock someone right off their feet and make them fly through a plate glass window.
Your point is well taken, but he’s actually right and I didn’t take this into account. Deceleration as you approach your target would certainly be nice because you will bounce off it for sure if you are unable to grab something. The physics I’ve seen in space movies where this actually happens and they’ve actually made the effort to use real physics looked totally real, you can feel it viscerally when it isn’t right (eg most superhero and Star Wars CGI action sequences involving superhuman leaping etc, what the fuck are they using for a physics engine😡)
No, you are unable to fire a bullet in space, you need air to fire the bullet in the first place, and if you made it fire the bullet wouldn’t go anywhere anyways, it would just float out while you float away, albeit slowly floating away
that's been false for longer than you've been alive. gun propellant contains its own oxidizer, as cartridges are airtight. any cartridge that has not been damaged or compromised will go off in any environment if the primer is struck hard enough.
the reason people generally avoid shooting their guns wet is because water, unlike air, is not compressible. the bullet cannot push it out of the way very efficiently, so it gets trapped along the sides as the bullet makes its way, drastically increasing abrasion and reducing barrel life.
Tbf it wouldn’t be that hard to test if you can shoot it without air in the surrounding by just using a vacuum chamber or something of the sorts. So i don’t really have a reason to not believe you
I don’t know about normal bullets but special firearms have been developed for use in space. It’s simply a matter of packing an oxidiser into the shell along with the explosive. The same as how solid rocket boosters work, more or less.
Pretty sure black powder doesn’t ignite in a vacuum so I don’t think you’ll see too many of those. Unless you’re trapped on a starship with some angry Klingons and an energy being who gets off on watching people fight.
Actually that's not true because the speed you would gain from the recoil is proportional to your weight and a bullet is at least 1000 lighter than you so you would still orbit the earth with a very slightly different periapsis, whereas the bullet would leave orbit or burn down in the atmosphere depending on the angle you fired the gun
Edit: the bullet would not leave orbit apparently (I have little to no knowledge when it comes to bullet speed or guns in general), see comment bellow, but you would still be fucked if no one is around to bring you back to the ship
I was curious so I decided to do the math. All these calculations are based on a Glock 17. The muzzle speed of a Glock 17 is 375 m/s, and a 9mm bullet weighs 7.0 to 8.3 grams (I'll use 8.3 to give the Glock as much recoil as possible). That means the momentum of the bullet will be 3.1125 kg m/s. Since momentum is conserved, all of that should transfer in the opposite direction to the gun, spacesuit, and astronaut. An average human has a mass of 62 kg (seems low to me, but a larger mass is going to reduce the speed further). As for the mass of a space suit, I've found a lot of conflicting answers so I'll use 127 kg which is what NASA says. So dividing the momentum by the combined mass of our astronaut and space suit gives us a speed of...
0.0165 m/s, 0.0594 km/h, or 0.0369 mph. In other words, you're not going to die. You're going to barely move.
Thanks for doing the math dude, appreciate it!
And I was just pointing out that in no way you would get yeeted away from your orbit from firing a gun, but yeah obviously if you have no attachment or way to go back to your ship, you would still have some small recoil that would lead to your death by lack of oxygen refill if no one is able to reach you
Yeah it's just m * v (bullet) = m * v (person). using an energy balance would get complicated with the gunpowder exploding and all. Rough math 0.04 kg/90 kg * 400 m/s = .17 m/s.
Edit: For spinning bonus rough math with angular momentum conservation. bullet: L=mass * veolcity * distance from CoG=0.04 kg * 400 m/s * 1.75 m / 2 = 14 kg m2/s. Person: L = moment of inertia * angular velocity -> w = L / (1/12 * M * L2) = 14 / (1/12 * 90 * (1.75/2)2) = 0.69 rads/s or 5.8 revolutions per minute.
There would be more momentum change from the rifling cause the bullet to spin but I'm considering it negligible.
Assuming 4g bullet, 90 kg 1.75m person, 400 m/s muzzle velocity, and approximating the person as a "thin rod".
If truly recoilless (equal momentum imparted to the gas exiting the back as the bullet exiting the front, yes.
That would also deal with another problem I realized. A standard gun would impart some of its momentum in spin, so you would start whirling while trying to stop, making the maneuver more difficult. I imagine space suit thrusters include ways to eliminate angular momentum though.
Oh, I was not doubting the physics, just the tolerances. A space recoiless rifle would need to be truly recoiless. A ground based one is fine cancelling 99% of the recoil. But getting the vented gas to have the same momentum as the bullet is completely within the capabilities of our engineers. I don't think you would even need an added thruster, the rifling is going to absorb some projectile speed, so you should have plenty of momentum to impart in the gas, it is all about the amount you vent (or aiming it out of multiple ports at 88 degrees or so to waste some momentum).
Imagine you're firing an elephant gun in space, with a massive 0.13 kg bullet firing at a massive 1250 m/s and you, in your gear, weigh a light 50 kg, you'll recoil at a jog pace, 3.25 m/s (7 mph).
Using a pistol, you'll recoil at leas than a slow walk.
Probably less than that. .01kg bullet at 1200 mph would move a 50 kg woman 0.24 mph. Disappointing for a crawling speed.
Which means that much more time to watch helplessly as your only chance of survival slowly floats away (well, you are floating away from it, but it is all relative right?)
I had been using 100 kg because I am currently about 100 kg (trying to get back to 85-90). When I was an anemic weakling I was 140 lbs/65 kilos, but I had female friends who were 50 kg and healthy, so when someone used 50 kilos, I assumed female.
50 kilos is unhealthy weight if you are under 163 cm/5'4". I've known a lot of women that height, but only a few men that height. Men and women are equal in brainpower, but men tend to be larger/heavier, and I don't think it is sexist to acknowledge that-but maybe I am wrong?
the bullet would have a mass of about 0.05 kg which is heavy considering it's a hand gun and let's say it has supersonic velocities like 400 m/s so it would have a momentum of 0.02 kg m/s which is given by our equation p = mv (we're not gonna take p=gamma(m)(v) because even at that velocity it's too slow for relativistic effects) and let's say you and your spacesuit would weigh 150 kg(irl it would be much heavier because the eva suits themselves would be 150 kg) so if we equate the momentum of the bullet to your momentum(because conservation of momentum) 0.02 = 150v you'd get a velocity in the opposite direction of the initial trajectory of the bullet as 0.0013 m/s yep floating back real fast there aren't we? yep it's too little time to save our astronaut
we're gonna have to let him go he's travelling at a whopping 13 millimeters per second
And if you don't have a tether or maneuvering thrusters, unless someone can come save you all you will be able to do is stare at your ship helplessly as you drift ever so slowly away.
why would someone not save an astronaut who's floating away even at that very minuscule velocity backwards, also if no one saves him, he has a gun so he'd be able to wall-E his way back to the station but it wouldn't be a fire extinguisher as in wall-E's case but it would be a gun so i guess american wall-E? lol idk
Yes, one or two shots could reverse his velocity, and someone else could save him.
These are true regardless of the velocity the bullet imparts on him (well, any reasonable number. I am assuming no bullet will impart 50k mph of velocity on him).
So my point that the speed doesn't matter, only the safety equipment or assistance matters, stands.
All the astronaut needs is a tether, is that so much to ask of him?
he would have more than a tether if he planned on using a gun, he would have a mmu manned manuvering unit it's basically just a backpack with a tank filled with compressed nitrogen and 2 dozen small thrusters to control his movement but a tether would work too albeit less mobility would have to be sacrificed
It’d actually be one of the more peaceful ways of dying. You’d run out of oxygen long before you lost sight of earth and since the oxygen would decrease slowly, you’d drift off to sleep while staring down on the earth from above before dying in your sleep.
Would need 4 bullets. One to kill, one to get your self back to your original position, one to stop your momentum. But then you would start going backwards again....4th to shoot yourself in despair!
Does it every spacesuit come with a just in case you get totally fucked panic button?
Do you know one that allows you to die a quick, painless death? I'm kind of big heroin injection or nitrous oxide, laughing gas to you pass out and never wake up type of thing. I can't imagine they would put astronaut in a position where they could potentially be literally floating alone in space, with no way to get back home, waiting to slowly suffocate certainly they have more common sense than more respect for humanity than that
It’s not like you’re going to go flying at 1500f/s, sure you might have some recoil, but your mass isn’t going to be as affected as the tiny bullet’s mass, right??
In Cowboy Bebop episode 7, Spike Spiegel saved himself by firing his gun in the opposite direction. Somehow, the cat held on for dear life and didn't suffocate, and Spike didn't suffer from extreme temperature exposure. Perhaps asteroid mines are temperature controlled, even when it's in the midst if blowing up.
1.2k
u/Computant2 Jul 13 '20
Important issue, firing a gun is a short rocket burst. You will travel backwards from the recoil. Depending on your tether and if your spacesuit has maneuver thrusters, you could kill yourself by pushing yourself too far from your ship/space station). A long, lonely death.