ABSTRACT
The U.S. Department of Defense manages the Navigation Satellite Timing and Ranging system (NAVSTAR), a network of 24 primary and additional backup satellites that broadcast Global Positioning System (GPS) timing signals worldwide. These satellites operate on six orbital planes 20,000 km above the earth’s surface in 12-hour orbital periods. Five monitoring stations passively track the satellites and a master control station sends navigation commands and signal uploads containing timing code. The system is designed to keep at least six satellites in line-of-sight from any point on earth at any time.
