GLONASS Ground Segment

GLONASS
Title	GLONASS Ground Segment
Author(s)	GMV
Level	Basic
Year of Publication	2011

The GLONASSGround Segment (also referred to as Control Segment or Operational Control System) is the responsible for the proper operation of the GLONASS system. The GLONASSControl Segment is composed by a network of Monitor Stations (MS), a Master Control Station (MCS), a backup of the MCS and the Ground Antennas (GA). In order to ensure operation and coordination of the entire system, the GLONASS ground segment determines satellite orbits as well as time and frequency parameters regularly. In addition, the health of all satellites is monitored continuously.These corrections and the navigation message are uploaded to the satellites through the Ground Antennas, which are co-located in four of the Monitor stations (Ascension Island, Cape Canaveral, Diego Garcia, and Kwajalein).

Introduction

The ground segment consists of the System Control Center and the Central Synchronizer situated in Moscow. Seven additional ground stations are maintained in the territory of the former Soviet Union, serving for orbit determination and satellite monitoring. These stations are equipped with radar, laser distance meters and/or telemetry. They are situated near the following towns:

• St. Petersburg TT&C
• Ternopol TT&C, laser ranging, monitoring
• Jenisejsk TT&C
• Komsomol’sk-na-Amure TT&C, laser ranging, monitoring
• Balchas Laser ranging
• Jevpatoria Laser ranging
• Kitab Laser ranging

System Control Centre (SCC)

The System Control Center (SCC) is responsible for satellite constellation control and management of GLONASSsatellites. It provides the telemetry, telecommand and control function for the whole GLONASSsatellite constellation. The SCC coordinates all functions and operations at the system level. It processes the information from the Command and Tracking stations to determine satellite clock and orbit states, and updates the navigation message for each satellite.

Command and Tracking Stations

The CTSs track the GLONASSsatellites in view and accumulate ranging data and telemetry from the satellites signals. The information from CTSs is processed at the SCC to determine satellite clock and orbit states and to update the navigation message of each satellite. This updated information is transmitted to the satellites via the CTSs, which also used for transmitting of control information.

The Command and Tracking Stations are composed by a main network of four Telemetry, Tracking and Control (TT&C) stations distributed throughout the Russian territory (in St. Petersburg, Ternopol, Eniseisk and Komsomolsk-na- Amure).

The CTSs ranging data is periodically calibrated using a laser ranging devices at the Quantum Optical Tracking Stations which are within GCS. Each GLONASSsatellite specially carries laser reflectors for this purpose. This network is complemented by other additional measurement stations (LS) in former Soviet Union territory (Balkhash in Kazakhstan, Evpatoria in Ukraine, Kitab in Uzbekistan), equipped with laser ranging and other monitoring facilities.

Central Synchroniser

The synchronization of all the processes in the GLONASSsystem is very important for its proper operability. There is the Central Synchronizer within GCS to meet this requirement. The Central Synchronizer is high-precise hydrogen atomic clock which forms the GLONASSsystem time scale. The onboard time scales (on a basis of satellite cesium atomic clocks) of all the GLONASS satellites are synchronized with the State Etalon UTC (CIS) in Mendeleevo, Moscow region, through the GLONASSSystem Time scale.