How do GPS satellites know your exact location instantly?

GPS satellites don't actually know your location at all — your receiver does the calculation. The satellites simply broadcast continuous radio signals containing their precise position and the exact time the signal was sent. Your GPS receiver picks up signals from at least four satellites simultaneously and measures how long each signal took to arrive. Since radio waves travel at the speed of light, the receiver calculates its distance from each satellite based on that travel time. Using a process called trilateration, the receiver compares distances from multiple satellites to pinpoint where those spheres of distance intersect in three-dimensional space. Four satellites are needed to solve for latitude, longitude, altitude, and clock error simultaneously. The whole calculation happens locally on your device, not on the satellites themselves.