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is the GPS myth unmythbustable?
On Aug 19, 7:12 am, Tom Roberts wrote:
On 8/18/11 8/18/11 - 7:59 PM, Henry Wilson DSc. wrote: All the orbiting clocks must be in very close synch...that is the only requirement for a good working system. This is most definitely NOT true for the GPS. shaking head All satellites must maintain as accurate of chronological time as possible. This requirement does not extend to any ground stations. shrug In particular, GPS time is REQUIRED to remain within 1 us of UTC modulo leap seconds. Where did you get this nonsense from? shrug It could not possibly meet this requirement without relativistic corrections. Hello? Did you not forget last night that you finally have demystified by understanding the meaning of solving for 4 unknown in 4 independent equations? Were you more sober last night? shrug As usual, you don't really know what you are attempting to talk about. Are you more sober now? Or last night? ... and as I said earlier, the error in the receiver's clock does not cancel out, but is ENGINEERED to be negligible compared to other contributions to the positioning error. Remember that it takes several seconds for a receiver to receive an entire almanac packet. The downlink bit rate is only 50 bits per second. That is bit not byte. shrug ... and if a GPS receiver attempted to make a position fix with only 3 satellites, then the positioning error would depend on the locations of those satellites -- if they all happen to be on one side of the receiver, then the positioning error will be enormous because the error in the receiver's local clock will dominate (it would also need to know which side of the earth it is on, which it might know from previous fixes). Of course modern receivers never do that, because there are always at least 6 satellites in view (the military worries about such things, including potential battle damage to the satellites). |
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