Satellite clock failures, one of the more probable
failures, is more likely to occur on the older Block-I
satellites, but this does not mean that it can’t happen
on the newer ones. When a satellite failure does
happen, it can result in undetected error of miles in
the position if a receiver is using the failed satellite
in its navigation solution.
When a satellite fails, even if that failure is detected
by an earth-based monitoring station, it can be some
time before an uplink to that satellite can occur.
During that time, there is no way for a GPS receiver
to know that the information from that satellite is
bad directly from that satellite’s transmissions. An
integrity monitor, such as RAIM when it is
available, protects you from false or misleading
navigation displays resulting from bad satellite
information.
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