Beidou 2 Navigation satellites

Application:  Navigation Operator:   Configuration:  DFH-3 bus

• The Compass Navigation Satellite System (CNSS), also known as Beidou 2, is being built to provide positioning and messaging services for both military and civil applications. It is the fourth of its kind in the world, after the U.S. Global Positioning System (GPS), Russian Glonass, and European Galileo. The programme was approved by the Chinese government in 2004. The system will initially offer high-precision positioning and navigation services to the Asia-Pacific region by 2014, and a global coverage by 2020.
• This series provides the satellites for the intermediate constellation called "Compass-M" in 12-hours orbits and for the inclined geostatonary (IGSO) constellation called "Compass-I"

CNSS Network:

The CNSS network consists of satellites placed on the geostationary orbit (GEO), inclined (55°) geosynchronous orbit (IGSO), and a circular 21,500km medium earth orbit (MEO). The first satellite, Compass-M1, was launched in 2007, followed by Compass-G2 in 2009. Five more satellites were launched in 2010, and four and five satellites have been scheduled to be launched in 2011 and 2012 respectively. Compass-IGSO3 launched in April 2011 allowed the system to start providing regional positioning service covering China and neighbouring countries, and the network will become fully functional with the launch of the last satellite in 2012.
• The CNSS can provide two types of services: a free service for civilian users with positioning accuracy of within 10m in central China (or 20m in neighbouring countries), 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). A licensed service with higher accuracy will be offered to authorised and military users. The system also retained the text messaging service originated from the Beidou 1 system.
• In the second phase of the programme, a global navigation satellite constellation consisting of 5 GEO satellites (58.75° E, 80° E, 110.5° E, and 140° E) and 30 IGSO and MEO satellites will be deployed by 2020. The network will be able to provide a 5m accuracy 2D positioning measurement (or 8m accuracy 3D measurement) for global users, with improved security and text messaging capacity.

The Satellites:

• The CNSS/Beidou 2 satellites have three variants: Compass-G, Compass-IGSO, and Compass-M.
• The Compass-G is a geostationary navigation satellite developed by CAST based on its DFH-3B platform. The satellite consists of the service module and payload module, and has a designed lifespan of 8 years. The onboard telemetry is unified C-/S-band. The propulsion is a 490N motor. The Compass-G is launched on a Changzheng 3C rocket carrying a single satellite.
• The Compass-IGSO is similar to the geostationary satellite in design, but is deployed in a 55° inclination geosynchronous orbit.
• The Compass-M satellite is deployed in 21,500~24,100km, 55° inclination MEO (intermediate circular orbit). An experimental Compass-M satellite based on the DFH-3B bus was launched in April 2007 to test the onboard payload.
• The operational Compass-M satellite, which is currently in development, will be 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 stabilised and has a power output of 1,500kW. The satellite can be carried on a liquid-propellant upper stage (satellite dispenser), allowing two or more satellites to be launched onboard a single launch vehicle.

Payloads:

• The Beidou 2 satellites carry two types of payloads: the Radio Determination Satellite Service (RDSS) and 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, frequency generator, a large L-/S-band antenna, and 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 antennas array, an L-band uplink receiver, laser corner-cube reflector for orbit determination, and multilateration unit.

Launch list:

Note:

• Four geostationary Beidou Daohang Shiyan Weixing (Experimental Beidou Navigation Satellite) satellites were laucnhed in 2000-2007.
• Since then the operational Beidou Daohang Weixing system has included one medium orbit satellite, five GEO satellites and five inclined-GEO satellites.