NAVSTAR GLOBAL POSITIONING SYSTEM

It was developed by Department of defence, USA.
FEATURES: 

1. Continuously provided global coverage.
2. It is a constellation of 21 satellites with 3 spares in semi-geosynchronous circular orbit at a height of 20,200 km.
3. 6 orbital planes, each inclined at 55 degree to equatorial plane.
4. The time required in one cycle of orbit is 12 hours.
5. 5 hour above horizon.
6. It has highly stable cesium and rubidium atomic clocks.
7. All data and information are transmitted at two frequencies which lies in L-band ( L1=1575.42 MHZ & L2=1227.60 MHZ ).