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Shenzhou 8 aces second docking test in sunlight

Posted: November 14, 2011

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Two Chinese spacecraft in orbit successfully accomplished another high-speed link-up Monday during a second docking demonstration designed to test sensitive optical rendezvous sensors against the harsh glare of the sun.

Cameras on Tiangong 1 captured this view of Shenzhou 8 backing away after undocking Monday.
Monday's test was crucial for Chinese engineers to gain confidence in the country's nascent rendezvous and docking technology before committing to a manned docking mission in the first half of 2012.

The Shenzhou 8 spacecraft disengaged from its Tiangong target module at 1127 GMT (6:27 a.m. EST), backed away to a distance of about 460 feet, then methodically re-approached the Tiangong spacecraft for a gentle docking more than 200 miles above China.

The second contact occured at 1153 GMT (6:53 a.m. EST), then hooks locked the vehicles together a few minutes later.

The second docking was timed at orbital sunset, when the sun slips below the limb of the Earth.

The two vehicles spent the last 12 days latched together after an initial automated docking Nov. 2. The first link-up occurred on the night side of the craft's orbit to reduce glare from the sun on rendezvous equipment.

But Chinese engineers wished to test the sensors with the glow of sunlight, which could interfere with readings from the instruments.

"If we can conduct dockings in all different kinds of light conditions, we'll have more freedom for future tasks," said Zhou Jianping, chief designer of China's manned space program.

Monday's demo was also the first time China tried to disconnect the Shenzhou and Tiangong modules.

"When we disconnect the two [modules], it means the final success of our first docking. We have 12 so-called locks between the two modules, and if any of those 12 failed, the mission failed," Zhou said in an interview on Chinese state television.

Controllers at the Beijing Aerospace Control Center monitored the stability and progress of the two vehicles, but Shenzhou 8's guidance computer controlled its movement away from and toward Tiangong 1.

Shenzhou 8 paused at at a distance of about 100 feet during its second approach to fine-tune its orientation relative to Tiangong 1.

Unlike the first docking between Shenzhou 8 and Tiangong 1 in early November, Chinese state television did not broadcast the event live. Chinese media provided a recap of the procedure shortly after it was completed.

Shenzhou 8 and Tiangong 1 will remain together for two days, then Shenzhou 8 will undock and its re-entry capsule will parachute back to Earth on Nov. 17.

The vehicles form a pairing stretching more than 60 feet long and up to 13 feet in diameter. Tiangong 1 is designed to control the stack during the docked phase with advanced control moment gyroscopes to maintain its orientation in space without using precious rocket propellant.

After Shenzhou 8's departure, Tiangong 1 will remain in orbit to receive two more Shenzhou missions next year. At least one of the flights will carry a crew of astronauts.

China has mounted three human space voyages since it joined the space-faring club in 2003. The most recent mission in 2008 included China's first spacewalk.

The proof of Chinese rendezvous and docking technology is crucial to the nation's plans of developing a 100-ton space station and assembling it in orbit by 2020.