Walking into the broad outer space seems romantic for common people but it is the toughest ever task for Chinese astronauts, said space experts in Beijing on Friday.

A scheduled 30-minute spacewalk, the highlight of China's third manned space mission, is expected to start at 4:30 PM on Saturday, said Wang Zhaoyao, spokesman with China's manned space program, at a press conference on Friday afternoon.

"Astronauts will have to follow a very complicated procedure," Wang said.

They will make a series of difficult moves in the space that can be easily done on the ground, Wu Bin, expert in charge of astronaut training with the China Astronaut Research and Training Center, told Xinhua.

Zhai Zhigang, the commander-in-chief and the No.1 astronaut, is the most likely to walk into the space.

"Head first and feet later. The astronaut is expected to greet to a camera on the spaceship surface as soon as his head and hands are out," Wu said.

Assisted by the No.2 astronaut who will stay in the orbital module during the process, he will take a test sample of solid lubricant from the surface of the spacecraft, which was placed there before the launch.

Then comes the most difficult move, the walk. The astronaut, tied to the spaceship with two safety wires, is going to walk along the orbital module exterior.

"Actually, it is not like walking but floating in the air," Wu said.

A set of handrails on the spaceship surface will help the astronaut to move, he said. He must make sure both the wires tied to the handrails before making any step forward.

"The Shenzhou-7 mission marks a historic breakthrough in China's manned space program. It is a great honor for all three of us to fly the mission, and we are fully prepared for the challenge," Zhai told a press conference on Wednesday at the Jiuquan Satellite Launch Center in northwest Gansu Province a day before his flight.

Zhai and other two colleagues, all 42, were chosen from the first group of 14 Chinese astronauts selected in 1998.

Before the spacewalk, lots of preparation must be done. The first is to put on the 120-kg-weigh space suit, or EVA (extra vehicular activity) suit. It will take hours, Wu said.

The two space suits were fixed on the module wall in parts when the spaceship was launched. The astronauts must assemble them on board.

Zhai and another astronaut Liu Boming have started the work since around 10:00 AM on Friday and the whole process may last for more than ten hours. It is the first time for them to do it under zero gravity as it is impossible to create a real condition of gravity loss on the earth.

"It is a delicate and tiring job," Wu said. For example, the practice to unpack the suits consist of 21 steps and each step is divided into sub-steps and detailed moves.

To ensure the safety of astronaut, the space suit is equipped with three oxygen tanks. An eight-meter-long electricity wire, linking the astronaut with the spaceship, will send his physiologic data back and act as a spare safety wire.

After putting them on, the astronauts will have to adjust the size of the suits, test the air tightness and all functions. "If all tests are fine, it means they successfully put the suits on," Wu said.

In the following 100 minutes, with the suits on, Zhai and Liu will rehearse what they will do in the spacewalk, for instance, how to open the door of orbital module.

Before the spacewalk, the orbital module must be cleaned and then separated from the re-entry module as it will play as an airlock between the spaceship main body and the space. The air pressure inside it will reduce to the outside level before the astronaut steps out.

All articles that can not stand low air pressure will be moved into the re-entry module, including foods, water feeder and cameras.

Another difficult move is to open the door between the orbital module and the outside, Wu said.

The astronaut will have to unlock the door and fix a protection cover on it against possible rubbing and cutting when he steps out. "What's the most difficult is that he has to finish all these with one hand while the other hand is to secure himself," he said.

On board of Shenzhou-6 spaceship in 2005, two astronauts practiced opening the door between the orbital and re-entry modules but they were wearing comfortable uniforms.

"This time, astronauts have to do the door in a bulky space suit. It will be very hard," Wu said.

When trained on the ground under simulated gravity loss, astronauts were able to open the door within a minute. But their performance may not be the same up there, he said. "We did not set a deadline for them."

When the astronaut finishes the spacewalk, a process vice versa will be done. He will enter the orbital module, feet first and head later, and lock the door. After the air pressure restores to the normal level inside, the two astronauts can take off the space suits.

(Xinhua News Agency September 26, 2008)