The Beidou Experimental Satellite Navigation System was developed in the late 1990s and first launched in 2000. The system was intended as tech demo for the development of a more sophisticated global satellite navigation system Beidou 2 (CNSS) currently in development.
In 1983, Chen Fangyun, China’s top space system engineering expert, proposed a regional navigation system with two satellites placed on the geostationary orbit. This theory was demonstrated on two Dongfanghong 2A communications satellites in 1989. The results of the demonstration showed that such a system was able to provide regional positioning measurement comparable in accuracy to the publicly available GPS signals.
In 1994, the Chinese government and military gave the go-ahead to the development and deployment of an experimental satellite navigation system based on the twin-satellite technology. The first pair of satellites, known as Beidou 1A and Beidou 1B, was launched in 2000. The system began to provide positioning service in late 2001.
A third satellite Beidou 1C was launched in 2003 as a system backup and also a testbed for RDSS and RNSS payloads of the next-generation satellite navigation system Compass (Beidou-II). The Beidou 1 service became available to civilian users in 2004. This made China the third country in world after the U.S. and Russia to have deployed an operational space-based navigation and positioning network.
The Beidou system covered the region between Longitude 70°~140°E and Latitude 5°~55°N. Two satellites are positioned in the GEO at 80° E and 140° E. The third (backup) satellite is positioned at 110.5°E.
The ground segment of the system included the central control station, three ground tracking stations for orbit determination (at Jiamushi, Khashi and Zhanjiang), ground correction stations, and user terminals (receivers/transmitters).
The satellites transmit at 2491.75+/-4.08MHz and the ground receiver can transmit back to the satellite on 1615.68MHz. The BeiDou reference-frame is the Beijing 1954 Coordinate System, with time referenced to China UTC as determined in Beijing.
The system provided positioning data of 100m accuracy. By using ground- and/or space-based (the 3rd and 4th satellites) differential methods, the accuracy was increased to under 20m. The system capacity was 540,000 user per hour, and up to 150 users simultaneously.
Beidou Experimental Satellite Navigation System
The Beidou 1 satellite was based on the DFH-3 satellite bus, and was 2.2 X 1.72 X 2.0 metres in size. A pair of solar panels had a span of 18.1m. The satellite weighed 2,200kg, and carried 1,100kg propellant for its rocket motor. Designed life span was approximately 5~8 years. The satellites were launched by the CZ-3A launch vehicle from the Xichang Satellite Launch Centre (XSLC).
Method of Operation
The central control station sent inquiry signals to the users via the two satellites. When the user terminal received the signal from one satellite, it sent responding signal back to both satellites. The central station received the responding signals sent by the user from two satellites, and calculated the user’s 2D position based on the time difference between the two signals. This position was then compared with the digital territorial map stored in the database to get the 3D position data, which was then sent back to the user via satellites using encrypted communications. The user could also transmit encrypted text messages (up to 120 Chinese characters) to the central station via the satellites.
As the system required dual-way transmissions between the user and central control station via satellites at high-altitude geostationary orbit, its user segment needed extra space for transmitter and a more-powerful battery. Therefore Beidou’s user segments were much bigger (20cm antenna), heavier and more expensive compared with GPS user receivers. Additionally, the number of users that could be served by the system simultaneously was limited by the communication capacity of the network.
Beidou 1 Network
- Beidou 1A – Role: Navigation. Programme: Beidou. Spacecraft: DFH-3A. Mass: 2,200kg. Contractor: CAST. Operator: Chinese government. Summary: The first Beidou navigation satellite, positioned in the GEO at 80°E.
- Beidou 1B – Role: Navigation. Programme: Beidou. Spacecraft: DFH-3A. Mass: 2,200kg. Contractor: CAST. Operator: Chinese government. Summary: The second Beidou navigation satellite, positioned in the GEO at 140°E.
- Beidou 1C – Role: Navigation. Programme: Beidou. Spacecraft: DFH-3A. Mass: 2,200kg. Contractor: CAST. Operator: Chinese government. Summary: The third Beidou navigation satellite, positioned in the GEO at 110.5°E.
- Beidou 1C – Role: Navigation. Programme: Beidou. Spacecraft: DFH-3A. Mass: 2,200kg. Contractor: CAST. Operator: Chinese government. Summary: The fourth (backup) Beidou navigation satellite. The satellite suffered from a control system malfunction, which resulted in the solar power penal unable to expand. After some adjustment work from the ground control station, the satellite was said to be fully restored. The satellite was placed into the GEO, presumably to complement the three existing Beidou 1 satellites by occupying the open slots at Longitudes 58.75°E.
Last updated: 3 April 2012