Used around the world for everything from emergency response to precision agriculture, GPS relies on 24 to 30 Earth-orbiting satellites, each outfitted with an atomic clock. These satellites transmit radio signals to receivers on the ground, like the one in your car's onboard navigation system. The receiver calculates the distance the signal has traveled by how long it takes to arrive. By repeating the process with at least four satellites, the receiver can pinpoint its own location anywhere on Earth. "The entire system," Gibble said, "depends on satellites and receivers having accurate clocks that can be precisely synchronized."
Close Window