Beidou Navigation Satellite System

The Beidou or Compass Navigation Satellite System is China’s second-generation satellite navigation system currently in the process of being deployed. Building upon the first generation Beidou System, which consisted of just 4 satellites, it is currently one of four navigation satellite systems worldwide. These being, in order of number of satellites deployed:

• Global Positioning System (GPS) of the United States
• Russia's Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS)
• China's Beidou Navigation System
• Europe's Galileo Navigation System.

Similar to the other systems, Beidou offers service to both civilian and military users. The civilian service available to all, which is downgraded from the military service, will provide an accuracy of 10 meters in the user position, 0.2 m/s on the user velocity and 50 nanoseconds in time accuracy.

Unlike the other systems, Beidou includes not only medium earth orbit satellites but also geostationary satellites. Their fixed position in the sky ensures continuous coverage to areas where the satellites are visible. The benefit is that is allows full service with just a limited number of satellites, namely 5 geostationary, 5 inclined geosynchronous and 4 medium earth orbit satellites.

The drawback is that coverage is limited to china and the area surrounding it. Global coverage will be achieved after all medium earth satellites have been launched and placed into orbit.

Another unique feature of Beidou is the ability for authorized users to send and receive text messages up to 120 characters. BeiDou will officially commence service for the Asia-Pacific region by the end of 2012 after completion of 12 months of trial service.

List of current Beidou satellites

Launch Date	Launcher	Satellite	Notes
04/14/07	LM-3A	Compass-M1	Test Satellite
04/15/09	LM-3C	Compass-G2	Not operational
01/17/10	LM-3C	Compass-G1	-
06/02/10	LM-3C	Compass-G3	-
08/01/10	LM-3A	Compass-IGSO1	-
11/01/10	LM-3C	Compass-G4	-
12/18/10	LM-3A	Compass-IGSO2	-
04/10/11	LM-3A	Compass-IGSO3	-
07/26/11	LM-3A	Compass-IGSO4	-
12/02/11	LM-3A	Compass-IGSO5	-
02/24/12	LM-3C	Compass-G5	–
04/29/12	LM-3B	Compass-M3	–
04/29/12	LM-3B	Compass-M4	–
09/18/12	LM-3B	Compass-M5	–
09/18/12	LM-3B	Compass-M6	–
10/25/12	LM-3C	Compass-G6	–