256
14 Pseudo-Ranging Radio Navigation Systems
Fig. 14.6 GPS orbital constellation
Fig. 14.7 Spectrum of GPS navigation radio signals
Table 14.4 Characteristics of
GPS orbital constellation
Number of NSV (regular)
32
Orbit altitude (km)
20,200
Number of planes
6
Semi-major axis (km)
26,560
Period
11 h 58 min
Inclination
55º
The GPS uses the 1984 World Geodetic System WGS-84. Another refinement
of the parameters of the WGS-84 (G1678) system took place in 2012. The GPS
time is associated with coordinated universal time UTC as observed by the United
States Marine Observatory (USNO). Nominally, the GPS time scale has a constant,
equaling to 19 s, discrepancy from the international atomic time TAI.
The GPS orbital constellation is controlled by the 2nd Operational Space Squadron
of the US Air Force Space Command. Currently, the GPS orbital constellation is
controlled by the second-generation ground control complex (Operational Control
Segment—OCS), which includes:
• the main control center for the GPS at Schriever Air Force Base;