Other Satellite Navigation Systems - Understanding GPS: Principles and Applications - page 603

ground support segment has been reduced to sites within Russia, with the exception
of one laser tracking site as indicated in Table 11.2. Further changes may also occur
in the future, including the addition of other control sites within the VKS control
network [1-4].

11.1.6.1 SCC
The SCC is a military complex run by the Russian Space Forces and is located in
Golitsyno-2, about 70 km southwest of Moscow. The SCC schedules and coordi-
nates all system functions for GLONASS [1].

11.1.6.2 Central Synchronizer
The central synchronizer forms GLONASS system time. Signals from the central
synchronizer are relayed to the phase control system (PCS), which monitors satellite
clock time/phase as transmitted by the navigation signals. The PCS performs two
types of measurements to determine the satellite time/phase offsets. The PCS
directly measures the range to the satellites by use of radar techniques. The PCS also
simultaneously compares the satellite transmitted navigation signals to a reference
time/phase generated by a highly stable frequency standard (relative error approxi-
mately 10 −13 ) at the ground site. These two measurements are then differenced to
determine the satellite clock time/phase offsets. The range of the satellite can only be
measured with an accuracy of 3m to 4m, which limits the accuracy of the time/
phase measurements. Measurements from the PCS are used to predict the satellite
clock time/phase corrections, which are uploaded by the ground station into the sat-
ellite. This comparison of each satellite's time/phases errors is carried out on at least
a daily basis [1, 19].

11.1.6.3 Command and Tracking Stations
The command and tracking stations (CTSs) measure individual satellite trajectories
and uplink required control and payload information to the satellite's onboard pro-
cessor. Trajectory tracking is carried out every 10 to 14 orbits. Tracking involves
between three and five measurement sessions, each lasting 10 to 15 minutes. Range

Table 11.2 GLONASS Ground Control Support Network

Site Function Former USSR Network Current Russian Network

System control center (SCC) Golitsyno-2 Golitsyno-2

Central synchronizer Moscow Moscow

Phase control system Moscow Moscow

Command and tracking
stations

St. Petersburg, Yeniseisk,
Komsomolsk, Balkhash,
and Ternopol

St. Petersburg, Yeniseisk,
and Komsomolsk

Laser tracking stations Komsomolsk, Balkhash, Kitab,

Evpatoria, and Ternopol

Komsomolsk and Kitab

Navigational field control
equipment

Moscow, Komsomolsk,
and Ternopol

Moscow and Komsomolsk