Beidou 1 Navigation satellites

Application:  Navigation Operator:   Configuration:  DFH-3 bus

Development History:

• In 1983, Chen Fangyun, China’s top space system engineering expert, proposed a twin-satellite 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 2. 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 1 system covers the region between Longitude 70°~140° E and Latitude 5°~55° N. Two satellites are positioned in geosynchronous orbit at 80° E and 140° E, with the third (backup) satellite positioned at 110.5° E. 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 Satellite:

• BD 1 (Beidou 1), in contrast to GPS and GLONASS, uses geostationary satellites. This reduces the number of satellites, but limits the coverage to a less than hemispherical area. The basic constellation requires 3 satellites.
• The Beidou 1 satellite was based on the DFH-3 satellite bus, and is 2.2 X 1.72 X 2.0 metres in size. A pair of solar panels has a span of 18.1m. The satellite weighs 2,200kg, and carries 1,100kg propellant for its rocket motor. Designed life span is approximately 5~8 years. The satellites were launched by the Changzheng 3A launch vehicle from the Xichang Satellite Launch Centre (XSLC).
• The ground control segment of the system consists of a central control station, three ground tracking stations for orbit determination (located at Jamushi, Kashi and Zhanjiang), ground correction stations, and user terminals (receivers/transmitters).

Method of Operation:

• Firstly, the central control station sends inquiry signals to the users via the two satellites. When the user terminal received the signal from one satellite, it sends responding signal back to both satellites. The central station receives the responding signals sent by the user from two satellites, and calculates the user’s 2D position based on the time difference between the two signals. This position is then compared with the digital territorial map stored in the database to get the 3D position data, which is then sent back to the user via satellites using encrypted communications. The user can also transmit encrypted text messages (up to 120 Chinese characters) to the central station via the satellites.
• The system provides positioning data with accuracy of 100m. By using ground- and/or space-based (the 3rd and 4th satellites) differential methods, the accuracy can be increased to under 10m and the timing accuracy 100 nanoseconds. The system capacity is 540,000 users per hour, and serve up to 150 users simultaneously. As well as positioning service, the system can also transmit encrypted text messages between the central control station and the end users.
• Because the Beidou 1 system requires dual-way transmissions between the user and central control station via satellites at high-altitude geostationary orbit, its user segment needs extra space for transmitter and a more-powerful battery. Therefore Beidou 1’s user segments are much bigger (20cm antenna), heavier and more expensive compared with GPS user receivers. Additionally, the number of users can be served by the system is limited by the communication capacity of the network.

Launch list:

External links:

• n2ya.com: Beidou satellites launch list.