Post by oldhippy on Sept 2, 2018 14:40:26 GMT
Do guns fire in space?
The vacuum of outer space will not be a problem for firing a bullet. Guns do not need oxygen to work. The "gunpowder" or whatever explosive is in the cartridge that holds the bullet is completely self contained and does not depend on the atmosphere. It has an oxidizer mixed with the fuel and is perfectly capable of firing in a vacuum. Even the primer which is struck by the pin of the firearm is completely self contained and will work in a vacuum.
The gun will work (very slightly) better in space. The bullet will not have to push and compress the air in the barrel as it exits the gun. Air will not slow down the bullet as it travels, so the range of the gun would essentially be infinite. It will curve eventually since it will probably still be in orbit, but it will have a different orbit than the gun/person that fired it. For example the International Space Station (ISS) has an orbital speed of roughly 17,000 miles per hour which is 7600 m/s. Muzzle velocities range from about 120 m/s to about 1,200 m/s depending on the gun and therefore the orbit of the bullet will differ from the orbit of the astronaut that fired it. In general firing anywhere in the forward direction of the orbit will result in a more eccentric orbit that will always stay at or above the ISS's orbit. If it is fired against the direction of the orbit, the bullet may end up dipping into the atmosphere and therefore deorbiting.
There is no need to "push" against anything for a gun to work. The difference between the mass of the bullet and the mass of the gun plus the person holding the gun will insure that the bullet gets almost all the kinetic energy of the explosive (Even though they both get the same momentum due to conservation of momentum.) However, assuming the astronaut is floating freely in space, if the line of the barrel does not point through the center of mass of the gun+astronaut, the firing of the gun will impart some small angular momentum to the astronaut.
To do some concrete calculations, the M4 carbine has a muzzle velocity of 910 m/s. the gun has a mass of 3.4 kg and the bullet mass is 4g. The ISS extravehicular space suit mass is about 124 kg and let's assume the astronaut mass is 70 kg. Then the mass of the gun, astronaut and space suit is about 197 kg. Given the muzzle velocity of 910 m/s, the bullet will have a momentum of 3.6 Ns (see 4 g * 910 m/s). For the astronaut+gun to have the same momentum, it will move at 18 mm/s (see 4 g * 910 m/s /197 kg), so the astronaut will have a very low velocity. The kinetic energy of the bullet will be 1656 J (see 4 g * (910 m/s)^2/2) whereas the astronaut+gun will have a kinetic energy of 0.02 J (see 122 kg * (18 mm/s)^2/2), so as promised almost all the kinetic energy is in the bullet. In the worst case if the gun was fired from near the astronaut's head the astronaut might end up rotating about once every 3 minutes which could be easily corrected by the thrusters the astronauts use to move about.
In terms of cooling, that would only be a problem if many rounds are shot — there will be radiative cooling in space, but no convective cooling, so it may overheat eventually. I believe the lubricants that are used in firearms have very low volatility so I doubt that they would dry out much faster than on the Earth.
The vacuum of outer space will not be a problem for firing a bullet. Guns do not need oxygen to work. The "gunpowder" or whatever explosive is in the cartridge that holds the bullet is completely self contained and does not depend on the atmosphere. It has an oxidizer mixed with the fuel and is perfectly capable of firing in a vacuum. Even the primer which is struck by the pin of the firearm is completely self contained and will work in a vacuum.
The gun will work (very slightly) better in space. The bullet will not have to push and compress the air in the barrel as it exits the gun. Air will not slow down the bullet as it travels, so the range of the gun would essentially be infinite. It will curve eventually since it will probably still be in orbit, but it will have a different orbit than the gun/person that fired it. For example the International Space Station (ISS) has an orbital speed of roughly 17,000 miles per hour which is 7600 m/s. Muzzle velocities range from about 120 m/s to about 1,200 m/s depending on the gun and therefore the orbit of the bullet will differ from the orbit of the astronaut that fired it. In general firing anywhere in the forward direction of the orbit will result in a more eccentric orbit that will always stay at or above the ISS's orbit. If it is fired against the direction of the orbit, the bullet may end up dipping into the atmosphere and therefore deorbiting.
There is no need to "push" against anything for a gun to work. The difference between the mass of the bullet and the mass of the gun plus the person holding the gun will insure that the bullet gets almost all the kinetic energy of the explosive (Even though they both get the same momentum due to conservation of momentum.) However, assuming the astronaut is floating freely in space, if the line of the barrel does not point through the center of mass of the gun+astronaut, the firing of the gun will impart some small angular momentum to the astronaut.
To do some concrete calculations, the M4 carbine has a muzzle velocity of 910 m/s. the gun has a mass of 3.4 kg and the bullet mass is 4g. The ISS extravehicular space suit mass is about 124 kg and let's assume the astronaut mass is 70 kg. Then the mass of the gun, astronaut and space suit is about 197 kg. Given the muzzle velocity of 910 m/s, the bullet will have a momentum of 3.6 Ns (see 4 g * 910 m/s). For the astronaut+gun to have the same momentum, it will move at 18 mm/s (see 4 g * 910 m/s /197 kg), so the astronaut will have a very low velocity. The kinetic energy of the bullet will be 1656 J (see 4 g * (910 m/s)^2/2) whereas the astronaut+gun will have a kinetic energy of 0.02 J (see 122 kg * (18 mm/s)^2/2), so as promised almost all the kinetic energy is in the bullet. In the worst case if the gun was fired from near the astronaut's head the astronaut might end up rotating about once every 3 minutes which could be easily corrected by the thrusters the astronauts use to move about.
In terms of cooling, that would only be a problem if many rounds are shot — there will be radiative cooling in space, but no convective cooling, so it may overheat eventually. I believe the lubricants that are used in firearms have very low volatility so I doubt that they would dry out much faster than on the Earth.
