Anjum Haseeb asks:

What is NAVSTAR navigation system?

Answer:

NAVSTAR stands for Navigation System using Timing And ranging.

It consists of  at least 24 satellites in 6 orbital planes.

Each satellite circles the Earth twice every day at an altitude of 20,200 kilometers.

The satellites are equipped with atomic clocks . They continuously broadcast the precise time according to their own clock, along with information including the orbital elements of their own motion, as determined by a set of ground-based observatories.

Find more details at

• http://www.spacetoday.org/Satellites/GPS.html
• http://en.wikipedia.org/wiki/Global_Positioning_System
• http://space.skyrocket.de/doc_sat/gps.htm
• http://www.spaceandtech.com/spacedata/constellations/navstar-gps_consum.shtml
• http://www.daviddarling.info/encyclopedia/N/NAVSTAR.html