At least three orbiting satellites have been malfunctioning. Experts have salvaged them all, aerospace scientists said in Beijing on Monday.

 

The experts from the Xi'an Satellite Monitor and Control Center reported that a satellite had gone out of orbit and somersaulted repeatedly in October 2006.

 

"Ground control temporarily lost control over the malfunctioning vehicle," said Dong Deyi, head of the center.

 

Scientists carefully studied previous orbiting statistics collected concerning the uncontrollable satellite. Experts analyzed computer simulations. They decided to try rescue attempts in December, an optimum time according to their calculations.

 

The scientists compiled convoluted orders into a short period of eight seconds. Then they repeatedly sent those orders into space. After continuous trials, the almost lost satellite started to respond and the Xi'an center finally gained control of it.

 

Shortly after the incident, Dong said, another satellite went out of orbit and was, again, recovered by the experts based in Xi'an.

 

In February 2007, the solar cells on another satellite went on the blink. Principal investigator Yu Peijun and his team in the Xi'an center calculated various signals emitted from the unstable satellite. They worked out contingency plans accordingly. After adjusting the angles of the solar panel, the Xi'an center regained control over the satellite.

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?First manned mission threatened by communication blackout

The Xi'an Satellite Monitor and Control Center also disclosed for the first time the danger met by the spacecraft, Shenzhou V, and China's first astronaut Yang Liwei.

It said Chinese aerospace experts saved the country's first ever manned space mission four years ago as the spaceship was faced with fatal impact while flying through the communications blackout area before landing.

Dong said that Yang lost every means to contact with the ground command and control headquarters as soon as entering the aerosphere, which fell in the worst case scenario prepared by the space mission team.

Every spacecraft would be covered by plasma as running through the aerosphere, according to experts. The plasma obstructs communications between the spacecraft and command and control center on the ground.

China was the third country, next to the former Soviet Union and the United States, to send people in space.

Although space scientists and technologists garnered experience in controlling the spacecraft after four unmanned tryouts, the headquarters designed a full list of contingency plans, including a possible emergency landing in Australian heartland.

"Even radar could not capture any signal from the returning module," Dong said.

After the Shenzhou V went out of the blackout area, Dong said, the echo signals from the spaceship were still volatile which sufficiently threatened a safe landing of astronaut Yang.

The Xi'an center, which is responsible for every landing of the Shenzhou spaceships since 1999, ordered implementation of the optical guiding and tracking system instead of communication-guided landing control, Dong said.

The aerospace technologists used cinetheodolites on the ground to measure spacecraft position and record the movement of the Shenzhou V. Precise positioning of the spacecraft enabled officers to properly control the slow-down parachute which was vital to a soft landing in Inner Mongolia.

However, the landing spot was nine kilometers east of the previously planned location, Dong said, citing that the rescue team reached astronaut Yang 12 minutes after his successful landing.

Onboard Shenzhou V, Yang spent 21 hours in orbiting the earth for 14 times from October 15 to 16, 2003.

Yang's adventure, however, was not the first time that Shenzhou spaceships were faced with challenges. Xie Mingbao, one key figure in managing the manned space mission, once revealed that at least four accidents occurred in the 11-year research and development leading to the first manned launch in 2003.

Just before its blast-off in January 1999, the first Shenzhou spaceship was diagnosed with a problem in its backup aerospace ecosystem. The headquarters decided to delay the planned launch.

The launch of the second experimental spacecraft, Shenzhou II, was neither smooth. Xie said an accidental drop left a small dent on the Long March rocket which was designated to carry Shenzhou II. It was after careful safety checkups that the spacecraft was allowed to go.

Shenzhou III experienced even worse fate. Technicians found no electricity in one socket of the lower part of the carrying rocket, which indicated a defect in electro-circuit design. The Long March rocket was then dismantled and transported back to Beijing for a complete check.

An unexpected chilly spell almost impeded the space journey of Shenzhou IV. Xie said the headquarters greatly worried about a one-week chilly spell, which dropped the temperature to minus 27 degrees Celsius. A low-tech solution helped ensure the planned launch -- Technicians covered the rocket with 200 quilts.

After his space-faring, Yang Liwei helped train his fellow astronauts and now becomes deputy head of the Space Medical Engineering Institute of the People's Liberation Army (PLA).

He was honored for his excellence of service at a gathering early this month marking the 80th anniversary of the founding of the PLA.

Yang was followed by Fei Junlong and Nie Haisheng who had toured the outer space for almost five days in October 2005.

China began its clandestine manned space program in 1992, which was coded as the 921 Project. Since then, China has spent at least 20 billion yuan (US$2.64 billion) in the project and sent three astronauts into orbit.

The Xi'an center, established on June 23, 1967, is located in the mountains of northwest China. It has monitored and controlled more than 100 satellites as well as the six Shenzhou spaceships. Official records now show that China has over 19 satellites orbiting the earth.

 

(Xinhua News Agency August 13, 2007)