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Issue #212 March 2008
Problem 1—The master clock on a GPS satellite is set to 10,229,999.99545 Hz. Why such an “odd” value?
Answer 1— The clock frequency on the satellite is set a little low in order to compensate for relativistic effects, so that the received frequency on the ground is the nominal rate of 10.230000 MHz. Both special relativity—the time dilation caused by the relative velocity of the satellite and receiver—and general relativity—the time dilation caused by the difference in gravitational potential between the surface of the earth and the orbit 12,000 miles up—come into play. The total average effect requires an offset of –4.45 × 10–10.
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