Blazing Satellites:Guns In Space

Formilab.com ^ | 10/2008 | John Walker

[ErnstStavroBlofeld]

When the movie Star Wars came out in 1977, remember how many jokes were made about Luke and Han blazing away at Imperial fighters with the ack-ack guns on the Millennium Falcon?

In the July 1998 issue of Spaceflight (the popular publication of the British Interplanetary Society), there's an article1 about the military version of the Soviet Salyut space station, which flew as Salyuts 3 and 5 between 1974 and 1977. (The name “Salyut” was applied to two entirely different space station programs, one military and the other civilian, which used completely different hardware built by different design bureaux.2 The hardware flown in the Salyut 3 and 5 missions was referred to as Almaz (Diamond) within the Soviet space program.)

Virtually no information was available about the military Salyuts until recently, when access was opened up to a full-scale training model at the Moscow Aviation Institute. Well, guess what—Salyut 3 had a machine gun. The station had a 23 mm rapid-fire cannon mounted on the outside, along the long axis of the station “for defence against US space-based inspectors/interceptors”. Combat engagements would have been leisurely by Star Wars or fighter jet standards, since the only way to aim the cannon was to point the entire station at the target, using its attitude gyros. A periscope connected to a visor on the main control panel allowed drawing a bead on the intended target

[ErnstStavroBlofeld]

Ping

[ErnstStavroBlofeld]

This was written in 1998 not 2008

[ErnstStavroBlofeld]

This is a 23mm gun supposedly on Salyut 3

[Nowhere Man]

I remember in David H. Ahl’s 1970’s era books on computer games in BASIC where you would type them in and play them, there was a starship battle simulator that used everything from lasers to conventional machine guns and cannons. I remember in physics class, I asked if you can fire a pistol or rifle in space and/or on the Moon and it would work because the powder has it’s own oxidizer to burn. I assume the Russki’s 23mm cannon works on that same principle.

[rfp1234]

Mel Brooks must love this headline.

[ErnstStavroBlofeld]

It must of have been difficult keeping the space station oriented and shaking to pieces when firing. They must have burned a lot of hydrazine keep it stable.

[ErnstStavroBlofeld]

Here is the website:

http://www.fourmilab.ch/documents/spaceguns/

[300winmag]

I assume the Russki’s 23mm cannon works on that same principle.

Gunpowder does have its own oxidizer along with the solid fuel, so no outside air is needed. That's also why guns can be fired underwater, but usually not very well. Glock sells special plastic seals for their handguns to seal in air for certain parts that won't work properly under water, but the ammunition is fine.

The soviet scientists were afraid of letting the cosmonauts fire the cannon while they were aboard, but they did fire it remotely when there was no crew in orbit. They said the recoil was so bad, they were afraid it would shake the spacecraft to pieces, so they didn't experiment with cannon after that.

[Lonesome in Massachussets]

Of course you can fire a pistol in space. The issue is recoil. If you read the article, they fire maneuver rockets to counter the recoil. You also need to make sure that the force of the recoil is acting along an axis that intersects the spacecraft's center of gravity, or else you'll spin wildly. That's why the gun was aimed by reorienting the entire spacecraft, otherwise it would have to have been mounted at the CG, which, surprisingly, is generally close to where the inertial navigational unit is. (There is a detectable oscillation in some spacecraft's “orbits” that is actually an artifact of the moment arm between the INU and CG and body rotation.)

[Yo-Yo]

That's why the gun was aimed by reorienting the entire spacecraft, otherwise it would have to have been mounted at the CG, which, surprisingly, is generally close to where the inertial navigational unit is. (There is a detectable oscillation in some spacecraft's “orbits” that is actually an artifact of the moment arm between the INU and CG and body rotation.)

First of all, the gun was mounted on the bottom of the spacecraft, well away from the center of mass, and would have imparted a rotational momentum to the spacecraft when fired.

Second, if you have a reference for this oscillation in spacecraft orbits due to the moment arm between the INU and the CG, I'd love to read it, because it runs counter to everything I've ever been taught about inertial naviagtion theory.

I was taught that you can mount the INS measuring unit anywhere on the vehicle and it will work equally well. If you take a spacecraft and rotate it 90°, which part of the spacecraft didn't rotate? All parts of the spacecraft rotated equally, therefore a rate gyro mounted at any location on the spacecraft would have sensed the rotation equally well.

[SunkenCiv]

Thanks ErnstStavroBlofeld!

[Lonesome in Massachussets]

For the INU, it's not orientation, it's location. The INU integrated rotation as motion and the dorks at [major national laboratory] did not take out the effect, basically producing a "best estimated trajectory" that had the object moving on an epicycle, which shows up as a more or less periodic range error in radar tracks.

The gun does not have to be at the center of mass to preclude it from causing rotation, the round and any gas ejected needs to exit the barrel with a momentum vector that lies along a line intersecting the CG. You could try to counter it with a thrust motor with an offsetting torque, but that seems awfully complicated. Basically you'd have to fire a round and then "despin" the vehicle. If you mount the gun so that is was always pointed away from, or through the CG, there would be no torque. Otherwise, good luck.