How fast would a bullet reach Mars (if shot from the ISS)?

Just curious. Here are some details

OK - now we are outside the station and we have a supply of oxygen for the explosion and we fire this gun. What would be the ultimate speed and how long would it take for the bullet to reach Mars? Does the explosion have any effect on the ISS and are the gravities of the Earth and the Moon significant? How many G’s due to the acceleration? My hard drive seems to pass 350G.

Not sure on the rest of the question (or if it would even leave orbit), but you don’t need external oxygen to fire a bullet - it’s included in the chemistry of the explosive propellant.

There might be other problems with firing a gun in a vacuum in space, but lack of oxygen for the explosion is not among them.

I don’t think you could do it - the bullet would have to escape Earth’s gravity, and if you can’t do that from the surface, you probably couldn’t do it from low earth orbit. Gravity isn’t very much weaker at that distance.

1220 m/s is not fast enough to escape Earth’s gravity starting from a Low Earth Orbit. To get to Mars, you need 4300 m/s.

With only an initial acceleration of the necessary Delta v, the path of the bullet will be a so-called Hohmann transfer orbit, which takes 8.5 months to reach Mars.
Of course you’d need improbable aiming skills to actually hit Mars without a mid-course correction.

ETA: Manduck, the Delta v is much less from Low Earth Orbit, not because the gravity is so much weaker there but because you’re already travelling at 7.8 km/s.

I guess they observed the speed in the Earth’s atmosphere

The distance between Mars & Earth varies.

… and you may just incite *them *into firing back! It’s easier for them – it’s all downhill!!!

Those are the numbers he was given. If you can add to the discussion by calculating with more accurate data, why don’t you?

Those are the numbers he was given. If you can add to the discussion by calculating with more accurate data why don’t you?

The muzzle velocity of a bullet may be a little faster in a vacuum than in atmosphere, but I doubt it will be four times faster.

As noted above, 1200 m/s isn’t enough to reach Mars. If you did decide to fire this gun outside the ISS, the best you could do would be to put it into an elliptical orbit. If I’ve done my sums correctly, this new orbit has gets as high as 27,000 km above Earth’s surface, but it doesn’t escape Earth’s gravity entirely. For comparison, geosynchronous satellites orbit around 36,000 km above Earth’s surface.

Disregarding the ISS’ orbital velocity, and also disregarding any gravitational influences, we can calculate time of flight for a bullet traveling the distance from Earth to Mars.

Assume 1220 m/s muzzle velocity per the OP.

Closest approach between the two: 56M km
time of flight: 531.27 days (about a year and a half)

Maximum distance betwen the two (when on opposite sides of the sun): 378,800,000 km
time of flight: 3593.7 days (almost ten years)

Firing in space, the muzzle velocity would be very slightly higher because the bullet does not have to accelerate the air in front of it inside the gun barrel. However, the mass of this air is very small (50-100 milligrams) and so its effect on the acceleration of a four-gram bullet is miniscule to begin with. Instead of 1220 m/s, you might see 1230 or 1240 m/s.

By ejecting the mass of the bullet in one direction, the ISS will be nudged in the opposite direction, but the effect will be miniscule. The bullet weighs a few grams, and the ISS weighs 376,000 kg (376,000,000 grams). If a four-gram bullet is launched from the ISS at 1220 m/s, the ISS will start moving in the opposite direction at 13 microns per second (0.0000467 km/hr) . This is additive (in vector fashion) to its orbital velocity of ~27,850 km/hr.

Teensy nitpick: you also have to include the mass and velocity of the expelled propellant along with the bullet. For the .223 WSSM, and playing around at Hodgdon’s website, I find the maximum powder load for the lightest bullet, 36 grains (2.33 grams), to be 47.5 grains (3.08 grams) of H414 powder. I’ve no idea what the average velocity would be for the bulk propellant gas stream, but it’d be higher in vacuum than down here. Call the whole thing double the calculated bullet-alone momentum? Still not moving the ISS that much, though you might give it an annoying torque if you’re out at one end of it?

Aside, looking at the ballistics for the .223 WSSM, .204 Ruger, etc… they all seem to top out at around 4300 fps or so. Is it the combustion rate of the propellant that sets the top end of velocity? Is it that modern chambers can’t handle higher chamber pressures? Is it that you’d need a 4 foot barrel to go faster? Just wondering, as modern saboted projectiles can go a lot faster.

Could you stand on top of the highest mountain on the Moon and shoot yourself in the back of the head with it?

Orbital velocity at the surface of the moon is 1680 m/s, so no, the Winchester (at ~1220 m/s) still won’t quite do it.

The moon has gravity, if less than that of the earth. The instant the bullet leaves the pistol gravity will start pulling it toward the surface. The lack of atmosphere plays no part in the gravitational attraction.

No, you’d need a muzzle velocity of about 1680 m/s to do that. You could do it on Triton, though, and on pretty much any moon smaller than that. (This would exclude the Galilean satellites of Jupiter, though, along with Titan.)

Hijack with a gun. What is the jurisdiction of this on the Moon - felony?:confused:

Right, but everything in orbit is being pulled toward the surface…it’s just moving quickly enough that the surface keeps “bending away” under it.

If you can achieve orbital velocity with your bullet, you CAN shoot yourself in the back of the head so long as there’s nothing to slow the bullet down and degrade it’s orbit…and the lack of atmosphere does matter for that.

As discussed in a thread yesterday, it isn’t quite that easy.