A Tianlian I-03 satellite was launched from the Xichang Satellite Launch Center in Sichuan province on Wednesday night, completing the country's first data relay satellite network.

The network will be crucial to the manned space program, which aims to build a space station around 2020, experts said.

The satellite was launched on a Long March 3C rocket at 11:43 pm, according to the center.

Developed by the China Academy of Space Technology, under the China Aerospace Science and Technology Corp, the satellite will join two orbiting predecessors to boost the network.

The first data relay satellite, Tianlian I-01, was launched in April 2008, and the second was launched in July 2011.

The center said the third satellite is expected to improve network coverage of measurement and control services for China's manned spacecraft as well as the planned construction of future space labs and a space station.

Liu Jin, deputy chief designer of the Tianlian I satellite project, said that scientists from the manned space program used to rely on ground stations and ships to track and control spacecraft.

But these methods only allowed spacecraft to be tracked in just 15 percent of their orbit. For the other 85 percent, there was no communication between the spacecraft and the ground control, he said.

After the first two Tianlian I satellites were launched, coverage expanded to 70 percent.

In the latest manned space mission, the Shenzhou IX spacecraft and Tiangong-1 space lab module circled around the Earth every 90 minutes. Thanks to the two Tianlian I satellites, communication between Earth and orbiting craft can continue for more than 60 minutes in each circle, he said.

This, obviously, gave ground control more precise knowledge of the orbiting craft and the three astronauts, allowing it to provide better support, he said.

"It's crucial to China's manned space program," he said.

And after a space station is assembled in 2020, astronauts on long missions will be able to contact ground control at any time.

The network will also offer data relay services for medium and low-Earth orbits as well as measurement and control support for launches.

Wednesday's launch marked the 166th mission of China's Long March series of rockets.

xindingding@chinadaily.com.cn

(China Daily 07/27/2012 page4)