Establishment of the GPS Epoch

At the start of January 6, 1980, GPS time began counting from its reference point, or epoch. This was not the day a complete navigation service suddenly became available. It established a shared starting point for a system whose satellites and receivers depend on precise timing.

The project grew from earlier U.S. military experiments with satellite navigation and accurate orbital clocks. These approaches were brought together during the 1970s. Experimental satellites tested the signals and timing technology before the full constellation was deployed.