+tkohler Posted March 3, 2003 Posted March 3, 2003 On a recent outing, I noticed that my eTrex Venture only expected to "see"* 6 satellites. Usually, I can expect to "see"* 8 or more from my location. I know that the Dept. of Defense can move them. Does anyone know if satellites have been moved to the Middle East as part of the military buildup? Has anyone else noticed this or is it just normal coverage. I couldn't find any articles about this in the news or in the GPS trade press. Tim (California) *by "see" I mean the number of satellites that the eTrex expects in the sky at the current time, not the number that I actually receive a signal from. Quote
+TEAM 360 Posted March 3, 2003 Posted March 3, 2003 I doubt they would be moving GPS-signal sending satellites anywhere...I am sure they have "roamers" with the high-tech cameras on them to go do the spying...on a similar note, I noticed an overabundance of "GPS" satellites when my Magellan was over in Red Square, Moscow. Quote
Kerry. Posted March 3, 2003 Posted March 3, 2003 The system being dynamic the number of sats you see will be different and change through out the day and this will also be different between different locations. Over 24 hours the average number one sees is "generally" 8 to 9 but ranges from 4/5 up to 12 and in some locations at times there's more than 12 but 12 channel receivers will only ever see 12 of these. What a receiver can see as opposed to what's in view can also be dependent on the receiver configuration and settings. Cheers, Kerry. I never get lost everybody keeps telling me where to go Quote
+Renegade Knight Posted March 3, 2003 Posted March 3, 2003 I don't know about you but if I had a bunch of satalites that let me wack enemy targets. I'd have spares on their side of the world. Wherever you go there you are. Quote
+arrowroot Posted March 3, 2003 Posted March 3, 2003 Unlike Geosynchronous satellites, such as those for DSS (DirecTV/EchoStar) and weather radar, the GPS birds are in Low Earch Orbit, and have an orbit of much less than a day. So they spiral around the world. The closer they are, the shorter the orbit time. They go all over the place. So sometimes they're here, sometimes they're there. They can't be 'directed' to go anywhere except for very minor course corrections. I am Arrowroot, son of Arrowshirt. I have many names, you know Quote
+Brian - Team A.I. Posted March 3, 2003 Posted March 3, 2003 For anyone interested, a link to the Constellation of GPS Satellites Quote
+shegget Posted March 3, 2003 Posted March 3, 2003 From "GPS Made Easy" by Lawrence Letham: "As a side note, during the Gulf War, the U.S. reconfigured the constellation to provide increased coverage in the Middle East. The change left people in California wondering why their receivers were not working as well as they use [sic] to work." The book says that 18 satellites is all that are required to provide 4-sat coverage over any area at all times, but the number of satellites varies from 24-29 usually, depending on upgrades, etc. It's very possible that the book is wrong, but it's food for thought... reconfiguring the orbits of the recievers seems like a feature you'd want to have, especially if (thinking like a military designer probably would) your enemy devised a way to take out one or two of your satellites so you didn't have as accurate of positioning over the battlefield... sean Quote
Kerry. Posted March 3, 2003 Posted March 3, 2003 At the start of the Gulf war there were only 16 GPS sats in orbit and even in the Gulf they only provided 19-20 hours of 2D coverage (basically only 3 Sats in view) and 15 hours of 3D coverage. The GPS satellite launched on the day of the Iraqi invasion was activated in a record (then) 22 days. Following satellite launches were placed in orbits to maximize coverage in the middle east. One certainly wouldn't want to be relying on 18 sats to give a min of 4 sats world wide all the time as that's probably a little optimistic. It's possible in theory but the system specs start to flounder at around the 22 mark. There's only 5 planes and 6 slots in each plane and since the Sats have to orbit and the geometry has to be maximum to be effective it is a jugling exercise that doesn't specifically favor one particular spot on the earth as was highlighted in the Gulf War. Cheers, Kerry. I never get lost everybody keeps telling me where to go Quote
+maleki Posted March 4, 2003 Posted March 4, 2003 There is a Sat Availability available from leica at: Leica Sat Availability It's a program along with an almanac of current sat info. It shows satellite availability from your location at all times of day. As mentioned earlier # of 'visible' sats vary thruout the day . So there are better times to 'cache' than others - although any time is good for me ... Not much help avail in this one but it seems to work if you can work your way thru it. Marty Quote
+Desert_Warrior Posted March 4, 2003 Posted March 4, 2003 quote:Originally posted by tkohler: Does anyone know if satellites have been moved to the Middle East as part of the military buildup Tim (California) Dunno, I have been watching for a few days now. Looks pretty normal to me, but I am several hundred miles from you, so it would be different. HOWEVER..... In a recent editorial by the Violence Policy Center (an arm of Sarah and the Brady Campaign to prevent Handgun Violence) they have stated that the single shot 50 caliber target rifle has enough power to shoot down aircraft and even satellites. (I will post it if anyone really wants to read this stupidity). So perhaps those target shooters who enjoy shooting 10 shots into one hole at 1000 yards now have a new hobby. And I am impressed. After reading the article, I am not sure if they believe it or if it is a joke! Just to level the playing field, do you really think someone can use a rifle, ANY RIFLE, and hit a target the smaller than the size of a car several dozens of miles in the sky moving at several thousands of miles per hour? How about the WW-II fighters with multiple automatic 50 caliber machine guns that shot up the enemy bombers, but they didn't go down with only one shot. NEXT: Nuclear 50 caliber rounds! Dunno, I will keep watching, but it looks pretty normal to me! Mike. Desert_Warrior (aka KD9KC). El Paso, Texas. Citizens of this land may own guns. Not to threaten their neighbors, but to ensure themselves of liberty and freedom. They are not assault weapons anymore... they are HOMELAND DEFENSE WEAPONS! Quote
+tkohler Posted March 4, 2003 Author Posted March 4, 2003 Thanks for all the insightful replies. I had read the passage in "GPS Made Easy" and that is what got me thinking. I don't think that someone could "take out" a satellite, rather that more satellites would reduce the number of areas with poor coverage, urban and natural canyons and etc. Tim Quote
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