GPS was originally developed by the U.S. Department of Defense to allow military units to determine their exact location anywhere on Earth. The system relies on a constellation of at least 24 satellites orbiting the planet, each carrying precise atomic clocks. By calculating the time it takes for signals from multiple satellites to reach a receiver, the device can determine its latitude, longitude, and altitude through trilateration. While it began as a military project (NAVSTAR), it was opened to civilian use in the 1980s and fully operational by 1995. GPS has fundamentally changed modern life, enabling everything from turn-by-turn car navigation and efficient maritime shipping to the synchronization of global financial networks and the functioning of ride-sharing apps like Uber. It is arguably the most important utility provided by space-based technology.