A series of US satellites that provides navigation data to military units and thousands of civilian users worldwide. There were 38 satellites operating in 2003, each with a life expectancy of 7.5 years. The spacecraft orbit the Earth every 12 hours, providing customers with precise navigation details of location, velocity, and time. Navstar's global positioning system is part of the US Department of Defense and is operated by the 50th Space Wing at Falcon Air Force Base, Colorado. The system was a strategic part of the Allied victory during the Gulf War of 1991.