Guns in Space

Monday, September 27th, 2010

If you were standing on the Moon and fired a bullet at the Earth, what would happen? Nothing special. The bullet would go up and come back down — unless you shot it really, really fast:

Well, assuming a maximum muzzle velocity of 1800 meters per second, you would at least be able to get the round up to lunar orbital velocity, so you could put the round into orbit around the moon if you aimed above the lunar horizon at just the right angle.

If you could squeeze a bit more thrust out of the round and get it moving up to lunar escape velocity (2380 meters/second), then assuming you were “leading” the Earth correctly, you could actually end up with a direct hit (with your round reentering the Earth’s atmosphere). Just remember, you cannot simply aim your gun at the Earth if you want to shoot it from the Moon though, but rather you have to aim towards where the Earth will be in its orbit in several days time. With a total delta-v just above lunar escape velocity, your round is gonna take awhile to cross the cis-lunar void and reach Earth, so you have to take that into account when you aim, otherwise the bullet might miss.

As the bullet from your Moon gun passed through an altitude of 38,759 miles (62,377 km) above the lunar surface, it would cross the lunar gravitational sphere of influence. From that moment onward, the gravitational source that would be most influencing the flightpath of the bullet changes from lunar to terrestrial. No longer is the bullet fighting the gravity of the Moon as it climbs upwards. Now, that bullet is actually falling towards the Earth, picking up speed.

Depending on what exotic metal you made the round out of, you could create one hell of a light show during the reentry into Earth’s atmosphere as it was vaporized by friction. Most “shooting stars” you see in the night sky are particles the size of a grain of sand burning up in the upper atmosphere, so something the mass of a .50 cal round could make for a pretty impressive sight as it comes smoking in.

If you wanted to try to put the bullet into any kind of decent Earth orbit (say, under 10,000 kms), I think you would have to try for some kinda crazy aero-capture maneuver where you aimed the round so that it just kissed the edge of the earth’s atmosphere, using atmospheric aerobraking to slow it down and capture it. I think your bullet would have to have some kind of final course correction capability built in in order to pull something like that off!

Would a gun work in space? Yes:

Just ask the Russians! They actually armed their Salyut-3 space station with a 23-millimeter NR-23 rapid-fire modified air-to-air cannon back in 1974. They even test-fired the damn thing and shot a metal target all to hell in low-Earth orbit!

Actually, it might surprise some people to learn that there is a handgun in space right now. Every Russian Soyuz vehicle carries a survival kit aboard in case during re-entry they land off course and end up in the Russian Steppes somewhere and have to wait a day or two to be rescued, and in that survival kit is a handgun. NASA’s official statement on the matter is simply that the gun is “is a piece of Russian equipment”. Every ISS crew member (doesn’t matter the nationality) is familiarized with the firearm during pre-flight training though.

Basically, every cosmonaut who has ever flown in space has been “packing heat”. Back in 1965 during Voskhod-2, Cosmonauts Aleksei Leonov and Pavel Belyayev landed way off course in the Urals somewhere and they actually had to use the gun from the survival kit to fend off wolves until the rescuers finally tracked him down the next day. I guess in a situation like that, a Russian handgun beats the crappy machetes that NASA puts in their survival kits!

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