GLONASS Ground Segment

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

The GLONASS Ground Segment (also referred to as Control Segment or Operational Control System) is the responsible for the proper operation of the GLONASS system.Like in GPS, the GLONASS Control Segment (or Ground-based Control Facilities) monitors the status of satellites, determines the ephemerides and satellite clock offsets and, twice a day, uploads the navigation data to the satellites.

Introduction

GPSGround Segment

SLR Station in Shelkovo (near Moscow)

The GLONASS ground segment consists of:

• A System Control Centre located at Krasnoznamensk.

• A network of five Telemetry, Tracking and Command centres (TT&C):
  • Schelkovo
  • Komsomoisk
  • St-Peteburg
  • Ussuriysk
  • Yenisseisk

• The Central Clock situated in Schelkovo (near Moscow).

• Three Upload Stations:
  • Yenisseisk
  • Komsomoisk
  • Schelkovo

• Two Laser Ranging Stations (SLR):
  • Schelkovo
  • Komsomoisk

• A network of four Monitoring and Measuring Stations:
  • Schelkovo
  • Krasnoznamensk
  • Yenisseisk
  • Komsomolsk
• Six additional Monitoring and Measuring Stations are to start operating on the territory of the Russian Federation and the Commonwealth of Independent States in the near future:
  • Yakutsk
  • Ulan-Ude
  • Nurek
  • Vorkuta
  • Murmansk
  • Zelenchuk

System Control Centre (SCC)

The System Control Center (SCC) is responsible for satellite constellation control and management of GLONASS satellites. It provides the telemetry, telecommand and control function for the whole GLONASS satellite 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 Command and Tracking Stations are composed by a main network of five Telemetry, Tracking and Control (TT&C) stations distributed throughout the Russian territory. The CTSs track the GLONASS satellites 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 Upload Stations, which also used for transmitting of control information.

Laser Ranging Stations

The high precision of laser ranging allows use of SLR as a single source of calibration data for GLONASS ephemeris determination, providing solution of following problems:

• Estimation of accuracy, and calibration of radio-frequency means for GLONASS orbit measurements.
• Providing SLR stations with geodetic-class RF navigation receivers connected to hydrogen maser frequency standards allows monitoring of on-board clocks and use of the data for operational control of GLONASS time and ephemeris data.
• SLR station coordinates are used as geodetic base for the GLONASS reference frame.
• SLR data are used to provide declared values of ephemeris precision.

Central Synchroniser

The synchronization of all the processes in the GLONASS system is very important for its proper operability. The Central Synchronizer is high-precise hydrogen atomic clock which forms the GLONASS system 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 GLONASS System Time scale.

System of Differential Correction and Monitoring (SDCM)

Russia is advancing its plan to implement a GLONASS System of Differential Correction and Monitoring (SDCM) covering the Russian Federation. The SDCM would perform integrity monitoring of both GPS and GLONASS satellites as well as provide differential corrections and a posteriori analyses of GLONASS system performance.

The SDCM orbit constellation will consist of three geostationary satellites from the multifunctional space relay system Luch (which means “ray” or “beam” in Russian). Luch 5A, to be launched in 2011 and positioned at 16°W longitude and Luch 5B, to be launched in 2012 and positioned at 95°E longitude, will transmit signals on an L1 frequency. Luch 4, to be launched in 2013 and positioned at 167°E longitude, will transmit on two frequencies. The three satellites will provide almost global coverage.

The SDCM will make use of 12 monitor stations currently in operation in Russia and one in Antarctica at Russia’s Bellingshausen research station. Eight more monitor stations will be added in Russia and five more outside Russia (Cuba, Brazil, Vietnam, Australia, and Antarctica). SDCM will also provide service through the Internet. A system website (www.sdcm.ru) already gives users information about real-time and a posteriori GLONASS and GPS monitoring