COMPASS (Beidou-II)

The Compass Navigation Satellite System (CNSS), also known as Beidou-II, was approved by the Chinese government in 2004.

After the U.S. Global Positioning System (GPS), Russian GLONASS, and European Galileo, COMPASS is the fourth Navigation Satellite System in the world.

The system was activated on a trial basis on 27 December 2011 and later became fully functional with the launch of the last satellite in 2012.

COMPASS was built to provide positioning and messaging services for China’s military and civil requirements.

It was planned to provide high-precision positioning and navigation services to the Asia-Pacific region by 2014. Compass was followed by the third stage of the Beidou Navigation Satellite System (BDS) – BDS-3.

The deployment of BDS-3 was completed in 2020, providing global navigation services.

The Compass Navigation Satellite System (CNSS) Network

The CNSS consists of:

  • 5 Geostationary Earth Orbit Satellites (GEO)
  • 5 Geosynchronous satellites (IGSO) in 55° inclination geosynchronous orbit
  • 1+2 Medium Earth Orbit (MEO) in a circular 21,500km orbit.

One year after the launch of COMPASS-IGSO5 in Dec 2012, the Compass Navigation Satellite System (CNSS) was activated on a trial basis providing coverage for China and its peripheral areas in the Asia-Pacific region.

The Satellites

The COMPASS satellites have three variants:

  • Compass-G – a Geostationary Navigation Satellite
  • Compass-IGSO – a Geostationary Navigation Satellite deployed in an inclined orbit
  • Compass-M – a Medium Earth Orbit Satellite

COMPASS-G

COMPASS-G is a geostationary navigation satellite. It was developed by CAST based on its DFH-3B platform.

The satellite consists of the service module and payload module. It has a designed lifespan of 8 years.

The onboard telemetry is a unified C-/S-band. The propulsion is a 490N motor.

The Compass-G is launched from the launch site in Xichang on a Changzheng 3C rocket carrying a single satellite.

COMPASS-IGSO

COMPASS-IGSO is similar to the COMPASS-G design as it is also based on the DFH-3B platform but is deployed in a 55° inclination geosynchronous orbit.

Compass-IGSO is launched from the launch site in Xichang on a Changzheng 3A launch vehicle.

COMPASS-M

COMPASS-M is an MEO satellite.

It is deployed in 21,500~24,100km, 55° inclination intermediate circular orbit. An experimental Compass-M1 satellite based on the DFH-3B bus was launched in April 2007 to test the onboard payload.

Following operational Compass-M satellites, Compass-M3 and Compass-M4 are based on a dedicated MEO satellite bus.

The satellite has a gross mass of 800kg and a payload capability of 280kg. The satellite is three-axis stabilized and has a power output of 1,500kW.

The satellite can be carried on a liquid-propellant upper stage, allowing two or more satellites to be launched onboard a single launch vehicle.

They are launched from the launch site in Xichang onboard CZ-3B/E.

Payloads

The COMPASS satellites carry two types of payloads:

  • Radio Determination Satellite Service (RDSS)
  • Radio Navigation Satellite Service (RNSS).

The RDSS payload is equipped on the Compass-G satellites only. The package includes:

  • A high-power S-band transponder.
  • An L-band low-noise amplifier.
  • A frequency generator.
  • A large L-/S-band antenna.
  • A C-band antenna.

The RNSS payload is equipped on all CNSS/BeiDou-2 satellites. The package includes:

  • An atomic clock.
  • An L-band transmitter.
  • Signal processor.
  • Transmitter antenna array.
  • An L-band uplink receiver.
  • Laser corner-cube reflector for orbit determination.
  • A multilateration unit.

Services

The CNSS was designed to provide two types of services:

Free Service For Civilian Users: with positioning accuracy of 10m in central China (or 20m in neighboring countries).

It offers a velocity accuracy of within 0.2 m/s and timing accuracy of within 50 nanoseconds in the single-way working mode (or within 2 nanoseconds in the dual-way working mode).
Licensed Service For Military Users: with much higher accuracy.

The system also retained the text messaging service originated from the BeiDou-1 system.

Did You Know?

BeiDou-3 followed BeiDou-2

The third phase of the BeiDou program, BeiDou-3, consists of a constellation of 35 more satellites deployed by 2020.

BeiDou-3 consists of:

  • 5 GEO satellites (58.75° E, 80° E, 110.5° E, and 140° E)
  • 30 IGSO and MEO satellites

The network is able to provide a 5m accuracy 2D positioning measurement (or 8m accuracy 3D measurement) for global users, with improved security and text messaging capacity.

Chronology

2007-04-14 – COMPASS-M1 – the first COMPASS/BeiDou-2 navigation satellite in the MEO.

2009-04-15 – COMPASS-G2 – the first COMPASS/BeiDou-2 navigation satellite in the Geostationary orbit. The satellite had drifted by 10 degrees from its original geostationary orbital slot by December 2009, suggesting that it may have lost control and been abandoned.

2010-01-17 – COMPASS-G1 – another GEO satellite positioned at 144.5°E.

2010-06-02 – COMPASS-G3 – third GEO satellite positioned at 84.7°E.

2010-08-01 – COMPASS-IGSO1 – first COMPASS/BeiDou-2 navigation satellite operating in the 55° inclination geosynchronous orbit.

2010-11-01 – COMPASS-G4 – fourth GEO satellite positioned at 160°E.

2010-12-18 – COMPASS-IGSO2 – second COMPASS/BeiDou-2 navigation satellite operating in the 55° inclination geosynchronous orbit.

2011-04-10 – COMPASS-IGSO3 – third COMPASS/BeiDou-2 navigation satellite operating in the 55° inclination geosynchronous orbit.

2011-07-27 – COMPASS-IGSO4 – fourth COMPASS/BeiDou-2 navigation satellite operating in the 55° inclination geosynchronous orbit.

2011-12-02 – COMPASS-IGSO5 – fifth COMPASS/BeiDou-2 navigation satellite operating in the 55° inclination geosynchronous orbit.

2012-02-25 – COMPASS-G5 –fifth GEO satellite positioned at 58.82°E.

2012-04-30

  • COMPASS-M3 – The 12th satellite of the Compass Navigation Satellite System (CNSS).
  • COMPASS-M4 – The 13th Compass Navigation Satellite System (CNSS) satellite.

Photo: Nicole.

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