What Would Happen If You Fired a Gun in Outer Space?

__

The triple barreled TP 82 pistol — twin 12.5x70mm smoothbore barrels over a 5.45×39 (the Russian 5.56 Nato equivalent) — went into space and back many times from 1986 to 2006 as part of the Russian Soyuz program. The stock-handle also served as a machete. The gun was packed in survival kits and intended for use here on Earth in the event the Soyuz capsule landed off-course and couldn’t be recovered. But, could it have been fired in space? Suppose the cosmonauts were attacked by aliens, or they wanted to do a fly-by strafing of some target on Earth?

We never got to find out. According to media reports, the ammo for this gun had become unusable by 2007 and it was determined that a more conventional semi-automatic pistol would be used on future missions.

I always assumed that a gun could shoot in space, and that the bullet would fly forever and you would fly backwards forever from the recoil. It turns out the real answers are much more interesting and complex.

According to this story, yes, guns can fire in space and they would seem to have a range of about 40,000 light years. And, you would have to be careful if you fired your space gun while in planetary orbit, as the bullet could go all the way around the world and hit you in the back. Here is the story from “Life’s Little Mysteries.”

_Fires can’t burn in the oxygen-free vacuum of space, but guns can shoot. Modern ammunition contains its own oxidizer, a chemical that will trigger the explosion of gunpowder, and thus the firing of a bullet, wherever you are in the universe. No atmospheric oxygen required.

The only difference between pulling the trigger on Earth and in space is the shape of the resulting smoke trail. In space, “it would be an expanding sphere of smoke from the tip of the barrel,” said Peter Schultz an astronomer at Brown University who researches impact craters.

The possibility of gunfire in space allows for all kinds of absurd scenarios.

Shooting stars

Imagine you’re floating freely in the vacuum between galaxies — just you, your gun and a single bullet. You have two options. You either can spend all of eternity trying to figure out how you got there, or you can shoot the damn cosmos.

If you do the latter, Newton’s third law dictates that the force exerted on the bullet will impart an equal and opposite force on the gun, and, because you’re holding the gun, you. With very few intergalactic atoms against which to brace yourself, you’ll start moving backward (not that you’d have any way of knowing). If the bullet leaves the gun barrel at 1,000 meters per second, you — because you’re much more massive than it is — will head the other way at only a few centimeters per second.

Once shot, the bullet will keep going, quite literally, forever. “The bullet will never stop, because the universe is expanding faster than the bullet can catch up with any serious amount of mass” to slow it down, said Matija Cuk, an astronomer with joint appointments at Harvard University and the SETI Institute. (If the universe weren’t expanding, then the one or two atoms per cubic centimeter encountered by the bullet in the near-vacuum of space would bring it to a standstill after 10 million light-years.)

Getting down to details, the universe expands at a rate of 73 kilometers per second per megaparsec (about 3 million light-years, or the average distance between galaxies). By Cuk’s calculations, this means matter that is 40,000 to 50,000 light-years away from the bullet would move away from it at about the same speed at which it is travelling, and would thus be forever out of reach. In the entire future of the universe, the bullet will catch up only to atoms that are less than 40,000 or so light-years from the chamber of your gun.

Speaking of you, you’ll be bobbing through space forever, too.

Shooting giants from the hip

Guns do actually get carried to space, though not quite to the void between galaxies. For decades, the standard survival pack for Russian cosmonauts has included a gun. Until recently, it wasn’t just any gun, but “a deluxe all-in-one weapon with three barrels and a folding stock that doubles as a shovel and contains a swing-out machete,” according to space historian James Oberg. The space guns are issued in case the cosmonauts need one back on Earth, so that they can protect themselves if emergency landing of their Soyuz spacecraft has left them deserted in a treacherous region. But still, cosmonauts in theory could shoot their guns before they landed.

So what if, during a spacewalk, a cosmonaut opened fire on Jupiter?

He or she should feel free to shoot from the hip. According to Robert Flack, a physicist at University College London, the enormous gravitational field of Jupiter is likely to suck in a bullet even if it is badly aimed. “Jupiter is so huge, it will capture the bullet and then it will follow a curved path down into the planet,” Flack said.

And as it does, it will pick up some serious steam. According to Schultz, if the bullet is shot straight toward Jupiter, the planet’s gravity will accelerate the ammo to the eye-popping speed of almost 60 kilometers per second by the time it crosses the gas giant’s threshold.

Watch your back

Shooting someone in the back is a cowardly act. In space, “theoretically you could shoot yourself in the back,” Schultz said.

You could do it, for example, while in orbit around a planet. Because objects orbiting planets are actually in a constant state of free fall, you have to get the setup just right. You’d have to shoot horizontally at just the right altitude for the bullet to circle the planet and fall back to where it started (you). And you’d also have to consider how much you’ll get kicked backwards (and consequently, how much your altitude will change) when you fire.

“The aim has to be perfect,” Schultz said.

Such a scenario isn’t as absurd as it sounds. In fact, Schultz said scientists at one point were considering setting up such a self-hit in space in order to investigate the effects of high-speed impacts._