The satellites were built by Rockwell Collins and launched by the Air Force. Each satellite has, among other things, radio transmitters, a receiver, and a set of atomic clocks. The DoD has four ground-based monitoring stations , and a master control station. The master control station is at Falcon AFB, Colorado. The monitoring stations track the satellites as they pass overhead, collecting data about satellite paths and times.
New data are uploaded to the satellites at least once a day.
The satellites then retransmit subsets of the orbital data as radio signals which can be received by GPS receivers. In other words, the exact location of each satellite is known, and, accordingly, every point on earth can be determined in reference to the global positioning system. With GPS, the satellites are the benchmarks. This is a predetermined, unique series of binary information that has characteristics of being random and therefore might otherwise be considered noise. It replicates the codes at the exact times they are being transmitted by the satellites.