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.
In: 9
You can run the maths to find out.
Momentum must be conserved, so if you fire a 100g bullet at 500m/s, (numbers made up) it has 50kgm/s of momentum in one direction, meaning the astronaut that fired it has 50kgm/s of momentum in the other direction (if we assume none of it was turned into angular momentum by firing off-center of mass).
For a human (and equipment) weighing 100kg total, this would mean they have been accelerated to 0.5m/s, which isn’t much, but if you were next to a relatively stationary object you would be able to notice the motion.
You can run the maths to find out.
Momentum must be conserved, so if you fire a 100g bullet at 500m/s, (numbers made up) it has 50kgm/s of momentum in one direction, meaning the astronaut that fired it has 50kgm/s of momentum in the other direction (if we assume none of it was turned into angular momentum by firing off-center of mass).
For a human (and equipment) weighing 100kg total, this would mean they have been accelerated to 0.5m/s, which isn’t much, but if you were next to a relatively stationary object you would be able to notice the motion.
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.
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.
>Will firing a 125 gram 9mm round have a noticeable effect on a 80,000 gram astronaut drifting away from his ship?
A 9mm gun could do that if fired correctly.
I do not know where you find 125-gram 9mm rounds, 20mm rounds fired from a Oerlikon 20 mm cannon used in WWII for air defense have rounds with masses around 125 grams.
Typical 9mm parabellum ammunition has bullet weights of about 8 grams. That is around 125 grains,A grain is 1/5760 troy pound = 64.79891 milligrams =0.06479891grams If you use a stupid non-SI unit use them correctly.
There are 3 to 9 grains of gunpowder that is pushed out the barrel t00, which is up to 0.6 grams so les say the bullet mass is 9grams
Astronauts out in space will not have a mass of 80 kg, they need a space suit to keep them alive, keep the pressure up, cool them down, provide oxygen, remove carbon dioxide, and have trusted to get back if an accident happens. The Extravehicular Mobility Unit (EMU) used on ISS has a mass of 145kg, add a 80kg astronaut, and the total mass is 225 kg. The russian suit has a mass of 110 kg, so a bit lighters.
That means the mass relationship is not 80000/125 = 1:640 but 225/0.009 1:25000. That is a difference by a factor of 200
Another missing number is the speed of the bullet because its momentum = mass * speed that matters. The speed of a 9mm bullet varies, I found an example of 300 to 400 m/s let’s use the higher one.
The momentum of the bullet and gunpowder is 0.009 *450 = 4.05 kgm/s
The astronaut with a mass of 225 kg has the same momentum at a speed of 4.05/225 = 0.018 m/s So if you fire the gun it could make the astronaut move.
This calculation assumes the recoil of the gun is directly in line with the center of mass, In practice it is quite unlikely that you fire a gun like that, If you fire a pistol like you normally do with the arm pointing forward the force will just cause you to rotate around your center of mass. That is the main problem of an improvised system. You need to align the trust with your center of mass
Look at https://en.wikipedia.org/wiki/Simplified_Aid_For_EVA_Rescue the rescue part of the US suit used on ISS There is a total of 24 gas trustees and they are spread out so they both can rotate you and keep the center of trust at you center of mass. I would assume there is a gyro in it that detects the rotation causes and just the trust that is provided
When astronauts do spacewalks that are tethered to the space station or space craft. If you move around you have two tethers and so one is always attached when you reposition the other.
There has been a few cases of astronauts floating free in space. This is when https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit was used in three missions in the 1980s. What is on their back is fundamental a space ship with trust that could accelerate by a total o 25m/s so it could bring you back efen if you fired a 9mm gun
>Will firing a 125 gram 9mm round have a noticeable effect on a 80,000 gram astronaut drifting away from his ship?
A 9mm gun could do that if fired correctly.
I do not know where you find 125-gram 9mm rounds, 20mm rounds fired from a Oerlikon 20 mm cannon used in WWII for air defense have rounds with masses around 125 grams.
Typical 9mm parabellum ammunition has bullet weights of about 8 grams. That is around 125 grains,A grain is 1/5760 troy pound = 64.79891 milligrams =0.06479891grams If you use a stupid non-SI unit use them correctly.
There are 3 to 9 grains of gunpowder that is pushed out the barrel t00, which is up to 0.6 grams so les say the bullet mass is 9grams
Astronauts out in space will not have a mass of 80 kg, they need a space suit to keep them alive, keep the pressure up, cool them down, provide oxygen, remove carbon dioxide, and have trusted to get back if an accident happens. The Extravehicular Mobility Unit (EMU) used on ISS has a mass of 145kg, add a 80kg astronaut, and the total mass is 225 kg. The russian suit has a mass of 110 kg, so a bit lighters.
That means the mass relationship is not 80000/125 = 1:640 but 225/0.009 1:25000. That is a difference by a factor of 200
Another missing number is the speed of the bullet because its momentum = mass * speed that matters. The speed of a 9mm bullet varies, I found an example of 300 to 400 m/s let’s use the higher one.
The momentum of the bullet and gunpowder is 0.009 *450 = 4.05 kgm/s
The astronaut with a mass of 225 kg has the same momentum at a speed of 4.05/225 = 0.018 m/s So if you fire the gun it could make the astronaut move.
This calculation assumes the recoil of the gun is directly in line with the center of mass, In practice it is quite unlikely that you fire a gun like that, If you fire a pistol like you normally do with the arm pointing forward the force will just cause you to rotate around your center of mass. That is the main problem of an improvised system. You need to align the trust with your center of mass
Look at https://en.wikipedia.org/wiki/Simplified_Aid_For_EVA_Rescue the rescue part of the US suit used on ISS There is a total of 24 gas trustees and they are spread out so they both can rotate you and keep the center of trust at you center of mass. I would assume there is a gyro in it that detects the rotation causes and just the trust that is provided
When astronauts do spacewalks that are tethered to the space station or space craft. If you move around you have two tethers and so one is always attached when you reposition the other.
There has been a few cases of astronauts floating free in space. This is when https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit was used in three missions in the 1980s. What is on their back is fundamental a space ship with trust that could accelerate by a total o 25m/s so it could bring you back efen if you fired a 9mm gun
You don’t actually need theory *or* a trip to space to test this. Try standing on a skateboard with something heavy, like a packed suitcase and throw it in a direction aligned with the wheels. You’ll roll in the opposite direction.
If you replaced the suit case with something even bigger and heavier, that you could barely lift, you’d go back even further.
If you replaced it with something so heavy that you couldn’t lift it, but you tried anyway, you’d go flying backwards because at this point “lifting and throwing” the object is indistinguishable from pushing against it, which illustrates how Newton’s Law applies to *everything*. The reason you can lift some things (a suitcase) and not others (a car) is precisely because of this equal and opposite reaction.
You don’t actually need theory *or* a trip to space to test this. Try standing on a skateboard with something heavy, like a packed suitcase and throw it in a direction aligned with the wheels. You’ll roll in the opposite direction.
If you replaced the suit case with something even bigger and heavier, that you could barely lift, you’d go back even further.
If you replaced it with something so heavy that you couldn’t lift it, but you tried anyway, you’d go flying backwards because at this point “lifting and throwing” the object is indistinguishable from pushing against it, which illustrates how Newton’s Law applies to *everything*. The reason you can lift some things (a suitcase) and not others (a car) is precisely because of this equal and opposite reaction.
You don’t have any significant friction, popping a champagne cork won’t give you a huge impulse but the velocity you’ll gain will last for thousands of thousands of miles, if you are orbiting at more or less the same speed as the ship popping a champagne bottle could easily provide the energy to get you back. Aiming it, however, would be more of a challenge.
You don’t have any significant friction, popping a champagne cork won’t give you a huge impulse but the velocity you’ll gain will last for thousands of thousands of miles, if you are orbiting at more or less the same speed as the ship popping a champagne bottle could easily provide the energy to get you back. Aiming it, however, would be more of a challenge.
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