Conceived in the 1960s as a system to provide positioning, navigation and timing for the U.S. military, today’s GPS system includes a constellation of more than 30 satellites orbiting Earth. Each satellite continuously broadcasts information such as its orbital parameters and precise time. On the ground, a GPS receiver captures signals from the satellites, using the information to determine its distance from each satellite. By doing this for three or more satellites, a receiver can compute its position in three dimensions.