#21
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Airspace
Jorge R. Frank wrote:
Alain Fournier wrote: Yes such orbits do exist. They are called geosychronous* orbits. You can't have one that stays over some northern (or southern) region, but russia could launch a satellite that stays above the Pacific, and the satellite could also go over some parts of eastern Siberia without going over another country. Launching *into* a geosynchronous orbit without the *transfer orbit* overflying any country would be a trick. Russia couldn't do it unless they put a launch site in eastern Siberia. They did build such a launch site in the 1990s. So that isn't a show stopper. But even without that launch site, it can be done. The transfer *orbit* doesn't have to be an orbit, it can be a quarter orbit. ESA couldn't do it because the transfer orbit would overfly Africa before reaching a high enough altitude (and low enough speed) that the Earth rotates under it and moves the groundtrack back over the Atlantic. ESA could do it by having the beginning of their launch trajectory being mostly vertical. Of course it would be a pain to use less efficient trajectories just to avoid overflying other countries. But not to the point where one would just abandon satellites. Even if launch cost were double what they currently are, satellites would still be launched. Alain Fournier |
#22
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Alain Fournier wrote:
Jeff Findley wrote: "Alain Fournier" wrote in message ... Jeff Findley wrote: "Pat Flannery" wrote in message dakotatelephone... Fusion295 wrote: I'm not an American, so please don't interpret this as a pretext for starting a flame war. Couldn't the US have just launcehd a satellite into an orbit with such an inclination that it's doesn't pass over the airspace of USSR? That would be hard to do unless you put it into a low inclination orbit, as anything of over 35 degrees would pass over some part the Soviet Union after a few orbits. And even worse, if you try not to overfly *any* other country, I'm not sure such an orbit even exists. Yes such orbits do exist. They are called geosychronous* orbits. You can't have one that stays over some northern (or southern) region, but russia could launch a satellite that stays above the Pacific, and the satellite could also go over some parts of eastern Siberia without going over another country. And the US could do the same going over Alaska and the Pacific. I suspect it would also be possible to do an orbit that would go over the contiguous 48 US states, then go around South America and come back. That would have to be a highly elliptic geosynchronous orbit, if it is possible. True, but that's *extremely* limiting, except for things like domestic communications satellites. I said in an earlier post that the US wanted to eventually develop spy satellites (optical and radio), which need to overfly the country of interest. In order to do that, they had to keep quiet about Sputnik. We agree here. Well maybe it wasn't an absolute necessity, but keeping quiet about Sputnik certainly did make things easier. Other than that, no you can't orbit Earth without flying over at least two countries, so you will overfly at least one foreign country. *Not to be confused with geostationary orbits. Geosynchronous orbits can go north and south but come back above the same points at each orbits. Geostationary orbits are a special case of geosynchronous orbits where the orbit is circular and the inclination is zero. I know, but a satellite trying to observe the central or eastern US which is in such an orbit would end up over Central America or even Cuba, not very friendly countries during the Cold War. Again, not very useful orbits. I haven't done the computations but I think you could have an elliptical geosynchronous orbit with perigee over central United States. At perigee the satellite must be moving eastward. With the right orbital elements you might be able to have it going mostly southward over the Atlantic, have apogee south of South America. At apogee the satellite must be moving westward. So for the northward part of the ride you could be above the Pacific. So maybe you could have a satellite that overflies central United States but no other country. The southern tip of South America extends past 50 deg S latitude. The US-Canadian border is at 49 deg N latitude. So I don't think it's possible to have an orbit that misses South America without hitting at least part of Canada. |
#23
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Jeff Findley wrote:
I know, but a satellite trying to observe the central or eastern US which is in such an orbit would end up over Central America or even Cuba, not very friendly countries during the Cold War. Again, not very useful orbits. At least for a first launch, it would have been possible for the US to put one into a orbit that didn't pass over the USSR, as Cape Canaveral is at around 28.5 degrees north, and the southernmost point of the USSR was at around 36 degrees north. The USSR on the other hand couldn't launch one that didn't pass over the continental US, as Baikonur is at around 48 degrees north*, and the tip of Florida at around 25 degrees north. * So is Kapustin Yar. Pat |
#24
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Jorge R. Frank wrote:
Alain Fournier wrote: Jeff Findley wrote: "Alain Fournier" wrote in message ... Jeff Findley wrote: "Pat Flannery" wrote in message dakotatelephone... Fusion295 wrote: I'm not an American, so please don't interpret this as a pretext for starting a flame war. Couldn't the US have just launcehd a satellite into an orbit with such an inclination that it's doesn't pass over the airspace of USSR? That would be hard to do unless you put it into a low inclination orbit, as anything of over 35 degrees would pass over some part the Soviet Union after a few orbits. And even worse, if you try not to overfly *any* other country, I'm not sure such an orbit even exists. Yes such orbits do exist. They are called geosychronous* orbits. You can't have one that stays over some northern (or southern) region, but russia could launch a satellite that stays above the Pacific, and the satellite could also go over some parts of eastern Siberia without going over another country. And the US could do the same going over Alaska and the Pacific. I suspect it would also be possible to do an orbit that would go over the contiguous 48 US states, then go around South America and come back. That would have to be a highly elliptic geosynchronous orbit, if it is possible. True, but that's *extremely* limiting, except for things like domestic communications satellites. I said in an earlier post that the US wanted to eventually develop spy satellites (optical and radio), which need to overfly the country of interest. In order to do that, they had to keep quiet about Sputnik. We agree here. Well maybe it wasn't an absolute necessity, but keeping quiet about Sputnik certainly did make things easier. Other than that, no you can't orbit Earth without flying over at least two countries, so you will overfly at least one foreign country. *Not to be confused with geostationary orbits. Geosynchronous orbits can go north and south but come back above the same points at each orbits. Geostationary orbits are a special case of geosynchronous orbits where the orbit is circular and the inclination is zero. I know, but a satellite trying to observe the central or eastern US which is in such an orbit would end up over Central America or even Cuba, not very friendly countries during the Cold War. Again, not very useful orbits. I haven't done the computations but I think you could have an elliptical geosynchronous orbit with perigee over central United States. At perigee the satellite must be moving eastward. With the right orbital elements you might be able to have it going mostly southward over the Atlantic, have apogee south of South America. At apogee the satellite must be moving westward. So for the northward part of the ride you could be above the Pacific. So maybe you could have a satellite that overflies central United States but no other country. The southern tip of South America extends past 50 deg S latitude. The US-Canadian border is at 49 deg N latitude. So I don't think it's possible to have an orbit that misses South America without hitting at least part of Canada. Remember we are talking about an elliptical orbit here. I'm not sure myself that such an orbit could avoid entirely South America and Africa, but I think it can be done. Alain Fournier |
#25
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"Alain Fournier" wrote in message ... Jorge R. Frank wrote: The southern tip of South America extends past 50 deg S latitude. The US-Canadian border is at 49 deg N latitude. So I don't think it's possible to have an orbit that misses South America without hitting at least part of Canada. Remember we are talking about an elliptical orbit here. I'm not sure myself that such an orbit could avoid entirely South America and Africa, but I think it can be done. Since you're asserting that it is possible, please prove it. I don't think it is possible because an elliptical orbit still has to exist in one orbital plane, which is what determines the north and south latitudes of the orbit. Altitude (i.e. circular versus elliptical) has nothing to do with the orbital plane of an orbit. If you don't want to do the math, there are orbit simulators out there. Determine the orbital parameters which solve the problem, then post them here so everyone can double check the result. Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon |
#26
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Jeff Findley wrote:
"Alain Fournier" wrote in message ... Jorge R. Frank wrote: The southern tip of South America extends past 50 deg S latitude. The US-Canadian border is at 49 deg N latitude. So I don't think it's possible to have an orbit that misses South America without hitting at least part of Canada. Remember we are talking about an elliptical orbit here. I'm not sure myself that such an orbit could avoid entirely South America and Africa, but I think it can be done. Since you're asserting that it is possible, please prove it. No I am not asserting that it is possible. I said so above. I just don't know that it can't be done. I don't think it is possible because an elliptical orbit still has to exist in one orbital plane, which is what determines the north and south latitudes of the orbit. Altitude (i.e. circular versus elliptical) has nothing to do with the orbital plane of an orbit. You are right about the orbit having to go as far north as it goes far south. So if it goes to 50 degrees south it must go to at least 50 degrees north. But the most northern point of the orbit doesn't have to be directly north of the most southern point. So if the most southern point is just south of South America, the most northern point can be in the northern Atlantic or northern Pacific. Imagine an elliptical orbit with its major axis on the equatorial plane and such that the satellite is going northward at perigee. The southern most part of the orbit is not the middle of the ellipse, it will be directly below the centre of Earth and the northern most part directly above the centre of Earth. So in the northward leg of the ellipse, the satellite will travel 180 degrees east in less than half the orbital period (less than 12 hours that is). So when it reaches its northern most point, Earth won't have had enough time to make half a rotation and the northern most part of the orbit will be east of the southern most part, potentially in the Northern-Atlantic. Conversely if the satellite is going southward at perigee, then the northern most part of the orbit will be west of Cap Horn, potentially in the Pacific. I don't think it would be possible to completely avoid over flying all other countries than the US with an orbit having its major axis in the equatorial plane. But the above shows that you can have the southern most part of the orbit south of Cape Horn and the northern most part not in Canada. And this will hold true for some range of angle of the major axis of the ellipse. If you don't want to do the math, there are orbit simulators out there. Determine the orbital parameters which solve the problem, then post them here so everyone can double check the result. Is it possible to find a trajectory that will not pass over any other country than the US, I really don't know, I don't know that it can be done and I don't know that it can't, but anyway I don't care. If someone wants to do the math to figure it out and doesn't know how to do it, I can explain how, but I doubt anyone really wants to do that. But I certainly will not go on the web to find an orbital calculator to do it. I can see why someone would want to do it with pen and paper, it can be a fun challenge, but making a computer do it is pointless, the computer won't think of it as a fun challenge. And nobody needs to know the answer. Alain Fournier |
#27
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#28
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Airspace
Dr J R Stockton wrote:
ISTM that Vanguard I did not need to, and probably did not, pass over any part of the Soviet Bloc, but could not have avoided crossing China. Orbital inclination was 34.25 degrees, which would have put it very near the southern border of the Turkmenistan SSR. Pat |
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