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GPS and Iridium
How dependent are various satellite systems like GPS and Iridium on
ground based support? I understand that these systems, as different as they are, both require ground based assitance to work. The GPS satellites need to be sent periodic corrections and the Iridium system needs attention from the ground. How long could they function without this ground based support? -Curious -Charles Talleyrand Note: I'm not sking how long these satellites will stay in orbit. A GPS satellite in orbit but sending an uncalibrated signal is actually worse than useless. Note: I don't care why the ground based support stopped, just the effect. Maybe because of a power outage or outer space aliens or legal changes or .... It just doesn't matter. |
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GPS and Iridium
"Charles Talleyrand" wrote:
How dependent are various satellite systems like GPS and Iridium on ground based support? I understand that these systems, as different as they are, both require ground based assitance to work. The GPS satellites need to be sent periodic corrections and the Iridium system needs attention from the ground. How long could they function without this ground based support? Note: I don't care why the ground based support stopped, just the effect. Maybe because of a power outage or outer space aliens or legal changes or .... It just doesn't matter. When I worked on Iridium, the last 18 months of its main software development effort at Motorola, they were contemplating a 24x7 ground support team of around 20 individuals. I don't remember if that was "per shift" or "total", though. Iridium takes a _tremendous_ amount of tweaking, since it depends on satellites knowing each others ephemeris to high accuracy, so the satellite to satellite laser communications can be kept aimed accurately, knowledge of the satellites own ephemeris and changes to it, so the solar panels can be kept faced toward the sun, so results of atmospheric drag can be overcome and pitch and yaw away from the intended orbit due to half a dozen un-"spherically symmetrical" forces that act on the satellites can be countered by correcting with gyroscopes or with steering gases. Too, the satellites don't last forever, and must be replaced on a continuing basis. I seem to recall that the planning included a set of hot spares in orbit, too. There are many ground stations, to send control signals to the satellites, and to provide connections between the satellites and the local "POTS" (plain old telephone system) and those, also, need ongoing maintenance. All of this means that Iridium would "stop working" fairly promptly if the ground crew went on strike. HTH xanthian. I haven't a clue about GPS, but some of the same considerations may apply. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
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