DATA RELAYS: TIAN LIAN

The application of communications satellites to data relay is included here. The Americans introduced what they called the Tracking and Data Relay SatelUte System (TDRSS) in the 1980s to support Shuttle operations. Hitherto, the Shuttle had communicated with the ground as its crew flew over tracking stations around the globe – an inefficient system which required continuous retuning to each new ground station it overflew. With TDRSS, the Shuttle sent its signals outwards and upwards – to the nearest of three TDRSS communications satellites in 24-hr orbit, which then relayed signals back to mission control. Russia had a similar system, Luch, for communicating with Mir. It was an expensive system, but one which produced comprehensive, seamless, round-the-clock communications between mission control and its astronauts.

Here, China adapted the DFH-3 communications satellite to fulfill a similar purpose for its manned spaceflight program. Tian Lian is apparently heavier, for it required the new CZ-3C launcher, suggesting that the CZ-3A was not powerful enough. The first data relay satellite, Tian Lian (“sky link”), was launched into geosynchronous orbit on 25th April 2008 in advance of the upcoming Shenzhou 7 mission. Tian Lian provided 50% coverage of Shenzhou’s orbits, but crucially during the space walk. Tian Lian 2 followed three years later, just in time for the Tiangong space station, with a third soon thereafter. It was not clear whether this was a spare or part of a three-satellite system. The series is noted in Table 6.11.

Table 6.11. Tian Lian series.

Both on CZ-3C from Xi Chang.