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#1
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Could a bullet be made any something that could go from orbit to Earth's surface?
I'm up on the Space Station and I go out for a nice little space walk. I
take along my specially designed hunting rifle and fire a bullet down at the planet. What would the bullet need to be made of for it to make it all the way to the surface and not burn up on entry to our atmosphere? Is there anything the bullet could be made of that would be able it to make the trip? And would the speed of the bullet affect its chances? Would also the bullet go weird like how bullets do when you shoot them into a pool of water? Idly curious, Scott Jensen -- Peer-to-peer networking (a.k.a. file-sharing) is entertainment's future. If you'd like to know why, read the white paper at the link below. http://www.scottjensenshow.com/P2PRevolution.pdf |
#3
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Could a bullet be made any something that could go from orbit to Earth's surface?
"Scott T. Jensen" wrote:
I'm up on the Space Station and I go out for a nice little space walk. I take along my specially designed hunting rifle and fire a bullet down at the planet. What would the bullet need to be made of for it to make it all the way to the surface and not burn up on entry to our atmosphere? Unobtanium. D. -- Touch-twice life. Eat. Drink. Laugh. |
#4
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Could a bullet be made any something that could go from orbit to Earth's surface?
Doug... wrote:
If you're in orbit, hanging in your suit outside of the ISS, you're traveling at about 17.5kmph. If you fire a bullet (and you'd better hope that you're braced against the station when you fire, or else the recoil might seriously test the design limits of your tether) straight "down" at the Earth, that bullet leaves the barrel with its muzzle velocity (several hundred mph, IIRC) but it's still going a LOT faster in the direction of orbit than it's heading "down." Since you're adding energy to the bullet's orbit perpendicular to its orbital direction, you're not going to raise or lower its *overall* altitude. Only adding energy into or against the orbital motion vector will raise or lower the overall orbit. What you *will* do is change the *shape* of the bullet's orbit. I haven't done the math, so I don't know how much the shape would be altered by an "average" gun and round's muzzle velocity. But let's say, for sake of argument, that the energy would push the bullet 50 miles closer to the Earth at its perigee. Because you haven't reduced the bullet's orbital speed, the 50-mile decrease in the orbit's lowest point is then matched by a 50-mile increase in its highest point. So, a bullet that started in a circular 250-mile orbit might end up in an elliptical 200x300-mile orbit. The average orbital altitude will change. The apogee will raise more than the perigee will go down. The total energy of the bullet does increase when it is fired. Not as much as if it was fired in the direction of motion but it still does increase. I computed that if the original orbit (orbit of ISS) is circular at 300 km; that the gun is pointed vertically towards Earth; and the muzzle velocity is 1km/s then the perigee would be 480 km below sea level. At that altitude drag is very important :-) The theoretical apogee (never reached because the bullet first hits Earth) would be at 1300 km. Oh, and the bullet's orbit will intersect ISS's orbit every time it crosses the 250-mile point, twice per orbit. During some of those intersections, ISS will be where the bullet is passing through. Now, the reality is that atmospheric drag (yes, there is still a very, very thin, but measurable, amount of atmosphere at 250 miles) will probably slow the bullet down a lot faster than it slows down ISS -- the bullet has a lot less mass. So it will probably re-enter in a few days, or weeks. At which point your original materials question comes into play... The fact that the bullet has less mass is irrelevant here. What is important is the density and the shape of the objects. The bullet would likely be much denser than ISS, that gives it less drag. But the lower perigee makes that not important. Alain Fournier |
#5
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Could a bullet be made any something that could go from orbit to Earth's surface?
Doug... wrote:
In article , says... I'm up on the Space Station and I go out for a nice little space walk. I take along my specially designed hunting rifle and fire a bullet down at the planet. What would the bullet need to be made of for it to make it all the way to the surface and not burn up on entry to our atmosphere? Is there anything the bullet could be made of that would be able it to make the trip? And would the speed of the bullet affect its chances? Would also the bullet go weird like how bullets do when you shoot them into a pool of water? Hmmm... I know you're asking a materials question, but the hypothetical you're using is flawed. If you're in orbit, hanging in your suit outside of the ISS, you're traveling at about 17.5kmph. If you fire a bullet (and you'd better hope that you're braced against the station when you fire, or else the recoil might seriously test the design limits of your tether) straight "down" at the Earth, that bullet leaves the barrel with its muzzle velocity (several hundred mph, IIRC) but it's still going a LOT faster in the direction of orbit than it's heading "down." Since you're adding energy to the bullet's orbit perpendicular to its orbital direction, you're not going to raise or lower its *overall* altitude. Only adding energy into or against the orbital motion vector will raise or lower the overall orbit. What you *will* do is change the *shape* of the bullet's orbit. I haven't done the math, so I don't know how much the shape would be altered by an "average" gun and round's muzzle velocity. But let's say, Ballpark. Say 600m/s. 1/4 of an orbit is 1350 seconds. 1/2 of time * velocity = 400Km. This would seem to indicate that it's going to go in. for sake of argument, that the energy would push the bullet 50 miles closer to the Earth at its perigee. Because you haven't reduced the bullet's orbital speed, the 50-mile decrease in the orbit's lowest point is then matched by a 50-mile increase in its highest point. So, a bullet that started in a circular 250-mile orbit might end up in an elliptical 200x300-mile orbit. Oh, and the bullet's orbit will intersect ISS's orbit every time it crosses the 250-mile point, twice per orbit. During some of those intersections, ISS will be where the bullet is passing through. There is very little chance of this. For an equatorial orbit, the chances are higher. However, for ISS-like orbits, the plane of the orbit is usually wrong, which makes it several orders of magnitude less likely. Now, the reality is that atmospheric drag (yes, there is still a very, very thin, but measurable, amount of atmosphere at 250 miles) will probably slow the bullet down a lot faster than it slows down ISS -- the bullet has a lot less mass. So it will probably re-enter in a few days, or weeks. At which point your original materials question comes into |
#6
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Could a bullet be made any something that could go from orbit to Earth's surface?
Alain Fournier wrote:
Doug... wrote: Oh, and the bullet's orbit will intersect ISS's orbit every time it crosses the 250-mile point, twice per orbit. During some of those intersections, ISS will be where the bullet is passing through. Now, the reality is that atmospheric drag (yes, there is still a very, very thin, but measurable, amount of atmosphere at 250 miles) will probably slow the bullet down a lot faster than it slows down ISS -- the bullet has a lot less mass. So it will probably re-enter in a few days, or weeks. At which point your original materials question comes into play... The fact that the bullet has less mass is irrelevant here. What is important is the density and the shape of the objects. The bullet would likely be much denser than ISS, that gives it less drag. But the lower perigee makes that not important. Not quite. The important bit is sectional density - mass per unit area. On this measure, the bullet is lots less sectionally dense than ISS, it will decellerate faster. |
#7
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Could a bullet be made any something that could go from orbit to Earth's surface?
Ian Stirling wrote:
Doug... wrote: In article , says... for sake of argument, that the energy would push the bullet 50 miles closer to the Earth at its perigee. Because you haven't reduced the bullet's orbital speed, the 50-mile decrease in the orbit's lowest point is then matched by a 50-mile increase in its highest point. So, a bullet that started in a circular 250-mile orbit might end up in an elliptical 200x300-mile orbit. Oh, and the bullet's orbit will intersect ISS's orbit every time it crosses the 250-mile point, twice per orbit. During some of those intersections, ISS will be where the bullet is passing through. There is very little chance of this. For an equatorial orbit, the chances are higher. However, for ISS-like orbits, the plane of the orbit is usually wrong, which makes it several orders of magnitude less likely. The plane of the orbit isn't important here. The bullet and ISS will both pass at the point where they where when the riffle was shot. If they both reach that point at the same time they hit each other. We don't care all that much at what angle they hit each other. To a first approximation, neither the bullet nor the space station know what is the spin axis of Earth. It makes no difference to them to be in an equatorial orbit or not. Alain Fournier |
#8
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Could a bullet be made any something that could go from orbit to Earth's surface?
Ian Stirling wrote:
Alain Fournier wrote: Doug... wrote: Oh, and the bullet's orbit will intersect ISS's orbit every time it crosses the 250-mile point, twice per orbit. During some of those intersections, ISS will be where the bullet is passing through. Now, the reality is that atmospheric drag (yes, there is still a very, very thin, but measurable, amount of atmosphere at 250 miles) will probably slow the bullet down a lot faster than it slows down ISS -- the bullet has a lot less mass. So it will probably re-enter in a few days, or weeks. At which point your original materials question comes into play... The fact that the bullet has less mass is irrelevant here. What is important is the density and the shape of the objects. The bullet would likely be much denser than ISS, that gives it less drag. But the lower perigee makes that not important. Not quite. The important bit is sectional density - mass per unit area. On this measure, the bullet is lots less sectionally dense than ISS, it will decellerate faster. Right. I wasn't thinking straight there. But I'm not quite sure that the bullet is lots less sectionally dense than ISS. ISS is mostly hollow. It weighs 187 tons, has about 1000 m^2 of cross section area. That is 187kg/m^2 or 19g per cm^2. That is more than normal bullets, but only by a factor of a few, so they are less sectionally dense than ISS but not really *lots* less. Alain Fournier |
#9
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Could a bullet be made something that could go from orbit to Earth's surface?
Scott T. Jensen wrote:
"Doug..." wrote: Since you're adding energy to the bullet's orbit perpendicular to its orbital direction, you're not going to raise or lower its *overall* altitude. Oh, I see. Hmmm. What if it was fired from a geo-stationary (fixed over a location on Earth) orbit straight down at the Earth? It would enter an elliptical orbit. The bullet would never get close to Earth. Alain Fournier |
#10
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Could a bullet be made any something that could go from orbit to Earth's surface?
"Scott T. Jensen" wrote in message
... I'm up on the Space Station and I go out for a nice little space walk. I take along my specially designed hunting rifle and fire a bullet down at the planet. Depending on the altitude of your orbit, and the muzzle velocity of the rifle, it probably will not hit the atmosphere at all and will wind up in a higher average orbit than you were in the first place. If you are in a very low orbit, and have a very high muzzle velocity, you might manage to hit the atmosphere. Rifles have muzzle velocities from (on the low end of the scale) 1000 foot per second to on the really high end of the scale 4000 foot per second. Orbital velocity is about 8000 meters per second or roughly 24,000 foot per second. If youm fire straight down with a 4000 foot per second rifle, the total velocity of the bullet with respect to the earth is going to be about V=(24000^2+4000^2)^.5=24,331 ft/sec. An orbit in low earth orbit takes about 90 minutes or about 5400 seconds, 1/36 orbit which will move you 10 degrees around the earth will take 150 seconds. In that time the bullet from a 4000 ft/sec rifle will travel 4000*150/5280=113.6 miles. But you would natually have moved about 61.7 miles in that direction in that time anyway for a 100 mile orbit.. If you were in a ~100 mile high or lower orbit, then probably the bullet will burn up. The higher up, the less likely. What would the bullet need to be made of for it to make it all the way to the surface and not burn up on entry to our atmosphere? Something that does not burn, and that stays solid at very high temperatures. A ceramic probably. Is there anything the bullet could be made of that would be able it to make the trip? And would the speed of the bullet affect its chances? Would also the bullet go weird like how bullets do when you shoot them into a pool of water? Idly curious, Scott Jensen -- Peer-to-peer networking (a.k.a. file-sharing) is entertainment's future. If you'd like to know why, read the white paper at the link below. http://www.scottjensenshow.com/P2PRevolution.pdf |
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