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Geosynchronous GPS?
Gary Coffman wrote in message . ..
On Wed, 13 Aug 2003 15:48:46 -0400, Robert Munck wrote: On Mon, 11 Aug 2003 04:50:49 -0400, Gary R Coffman wrote: ... Just put a couple of kilos of gravel in the same orbit but going the other way, and pretty soon no comsats. You'd have to be mighty lucky to hit even one comsat by doing that. ... A comsat doing good station keeping could be anywhere in a cubic mile volume around the ideal GSO track. ... a comsat only presents a few square meters of cross section along the orbital track. Not by my figures. If there are only 1,000 pieces of gravel and a given comsat takes up 1/1,000,000th of the (one-mile cross- section of the) orbital track, you've about one chance in 1,000 of hitting it. You're implicitly assuming that the gravel is randomly distributed. Obviously, wouldn't be at first. But our experience with debris patterns is that they become randomly distributed over long time scales. I'm thinking here of Markov processes. All the sites that can have positive probability eventually will with a decay process from the overpopulated orbital states to the underpopulated states. But the gravel is moving through the entire GSO track twice a day (at 6 km/s relative) so it has a good chance of hitting one comsat every day or two and all of them within a year or two. You're implicity assuming the gravel randomly changes squares each orbit. snip That is a good assumption to make particularly with perturbations from the Sun and Moon. Karl Hallowell |
#12
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Geosynchronous GPS?
"Ultimate Buu" wrote:
Wouldn't it be prudent for the U.S. to develop a GPS-like system which is based in a geosynchronous orbit, as both the Chinese and Russians are developing ASW (anti-satellite warfare) systems? At the very least such a system should be used as a backup since most precision weapons rely on GPS. It would be much harder for the Chinese to knock out a geosynchronous satellite and it would be almost impossible to do so using lasers (their preferred method at this time). Any nation which can deliver satellites to GEO can also deliver anti-satellite weapons to GEO. China and Russia certainly can, even India can. Also, as others have pointed out, the GPS constellation is already in a pretty high orbit, which takes nearly as much energy to reach as GEO, so they're about as safe as can be orbit wise. As nobody's pointed out yet so far as I can see, the GPS constellation is already designed with ASAT capabilities in mind. The electronics are hardened to a certain degree from EMP. There are, classified, procedures for avoidance of ASAT weapons. And there are orbital spares designed to provide service in the case of lost satellites. Since the system is designed with a fair degree of redundancy when the satellite constellation is "full" (i.e. there are usually more satellites in the sky at any given time for any given location than are absolutely necessary for geo- location) it would take a large number of lost satellites to create a service loss. Think about it a second, the GPS system was designed in an era when the Soviets already had a demonstrably functional ASAT system, and when the most likely major war larger than a regional conflict was a global exchange of thermonuclear warheads etc. GPS was designed from the get go to have the maximum chance of surviving *that*. In comparison, some middling state or even a big regional power (like China) developing a functional ASAT weapon is small potatoes. Finally, as for your comment that the Chinese prefer to use lasers as an ASAT weapon, I think you ought to lay off the crack pipe just a teensy bit. But that's just a suggestion. |
#13
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Geosynchronous GPS?
"Sander Vesik" wrote:
Sounds like this would merely lead to development of better sattelite knockout weapons... This planet definately doesn't need yet another dumb arms race. Everyone says that, except there aren't usually a whole lot of takers for being on the losing side of an arms race. |
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Geosynchronous GPS?
"Alex Terrell" wrote:
As mentioned, there half way to GEO (energetically, almost all the way there). Another defence would be to have secret, dormant GPS satellites (in a stealth shroud?) which would activate if other ones were knocked out. I wonder if they have that already? The GPS constellation nominally contains 24 satellites, but needs only 21 satellites to meet the minimum coverage requirements (near global coverage, periods of degraded accuracy beyond about 10m lasting only around an hour or less and limited in extent). The current GPS constellation has 27 functional satellites. The modern GPS satellite configuration doesn't really use "spares" per se but something more along the lines of "failure tolerant configurations". The current configuration can handle 2 satellite losses without hardly a hiccup. And decent service with only as few as 18 satellites is possible (but would require repositioning, I think). It is, of course, unknown whether the US military maintains secret orbital spares for GPS. Though the amateur satellite tracking community is good enough to where I'd think that fairly unlikely (though not entirely out of the question). |
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