The NAVSTAR Global Positioning System is a space-based radio navigation network providing precise positioning and navigation needs of all the military services. In the fully operational configuration, there will be 18 satellites in six orbital planes with an orbit period of 12 hours at 10,900 nautical miles altitude. Each satellite transmits three L-band, pseudo-random noise-coded signals, one S-band, and one ultra high frequency for spacecraft-to-spacecraft data relay.