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
>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
Latest Answers