Radio Navigation Missions

The radio navigation satellites (Global Positioning System (GPS), and GLObal'naya Navigatsionnay Sputnikovaya Sistema (GLONASS)) are United States and Russian satellite constellations, respectively.

The GPS and GLONASS satellite constellations provide time, space, and position information to the user. GPS is now widely used in geodesy and surveying. GPS provides excellent relative positions (1-2 millimeters) over few kilometer distances, but errors increase over much longer distances.

The positioning satellites are large, irregularly shaped, and in relatively high orbits (approximately 20,000 Km).

Currently, only two of the GPS satellites are equipped with retro-reflector arrays. However, each GLONASS satellite is equipped with a retro-reflector array. NASA convinced the U.S. Military in the mutual benefit in placing retro-reflector arrays on GPS satellites and the actual GPS retro-reflector arrays were built by the Russians in a cooperative agreement.

By using SLR Precision Orbit Determination (POD) of GPS satellites in conjunction with collocated GPS and SLR equipped observatories, the accuracy of the International GPS Service (IGS) network can be improved. In addition, the accuracy of the transfer of time between the GPS satellite and the GPS receivers can be improved by knowing the exact positions of the GPS satellites determined by SLR POD.

The GLONASS constellation currently consists of approximately 24 satellites, but only 2 are routinely supported by the SLR community.

Responsible Government Official: Carey Noll
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