Worth two observation hours per Mr. Percival
On this episode of astrocast, we learn about GPS satellites, ranging from their invention to the way they function.
As people might expect, GPS was originally a secret military technology (like many great household inventions before it). The government needed its soldiers to be able to complete missions without having to consult maps (which might ruin a mission due to a lack of landmarks, a false sense of direction, an old map, the soldiers being spotted by the light they are using to see the map, or a host of other possibilities). So, they used the accuracy of the newly-invented atomic clock to make satellites that, when at least three were in range of you, could tell you your exact position at any given time. However, when the GPS finally became public, the military was apparently afraid that terrorists could use GPS to guide bombs to a specific location from a long distance, so they programmed in random timing errors, decreasing accuracy significantly.
The errors are gone now, and with many modern devices using GPS along with other technologies (cell phone towers, wireless networks, etc.), GPS is accurate to within the possible timing errors, at the best of times resulting in a possible area less than the size of a Starbucks!
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