China began counting down Thursday to an evening rocket launch that will put a crew of three men into space, including one who will make the country's first spacewalk.

Underscoring the mission's heavy political overtones, Chinese President and Communist Party head Hu Jintao was shown live on state television hailing the astronauts at the launch site near the northwestern town of Jiuquan.

"You will definitely accomplish this glorious and sacred mission. The motherland and the people are looking forward to your triumphant return," Hu told the three, who were dressed in their flight suits and behind glass to avoid germs.

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The Shenzhou 7 mission, expected to last three to four days, is China's most challenging since it first launched a person into space in 2003.

The spacewalk, known formally as an extra-vehicular activity, or EVA, is expected to help China develop the technology for docking two orbiters to create China's first space station in the future.

The launch window for the mission at the Jiuquan launch site in northwestern China had been set at between 9:07 p.m. and 10:27 p.m. (9:07 a.m. and 10:27 a.m. EDT) on Thursday.

The spacewalk could happen either Friday or Saturday depending on how well the astronauts adapt to weightlessness and other physical demands of their environment, according to the China Manned Space Engineering Office.

The walk will take place in the afternoon local time, with the astronauts returning to Earth soon afterward, the office said.

Speaking at a regularly scheduled news conference, Foreign Ministry spokesman Liu Jianchao repeated China's stance that space missions should be "for peaceful use."

"The Shenzhou 7 mission is part of our effort to explore and make peaceful use of outer space. We believe this will further promote our space flight technology and make contributions to the peaceful use of outer space for all human beings," Liu said.

In a sign of the manned space program's burgeoning confidence, the director of the China Astronaut Research and Training Center said he wants to accept trainees from other nations as well.

In comments carried by the official Xinhua News Agency, Chen Shanguang said one of his center's goals has long been to train international astronauts.

Although China has largely gone it alone in developing its manned space program, Chen said international cooperation was an "inevitable trend in manned space flight" due to the expense and complex technology involved.

Since 1998, China has trained a corps of 14 astronauts drawn from the military, known as "yuhangyuan" in Chinese, some of whom received initial training in Russia.

The two astronauts who don spacesuits for the Shenzhou 7 spacewalk will be "supported by Russian experts throughout the mission," space program spokesman Wang Zhaoyao told reporters Wednesday.

Only one will actually leave the orbiter module to retrieve scientific experiments placed outside. One of the astronauts will wear China's homemade Feitian suit, while the other will wear a Russian-made suit.

Wang said Russian support for the latest mission could translate into a broader relationship in future.

"The successful cooperation on the Shenzhou 7 manned mission will create favorable conditions for future cooperation between our two countries," Wang said, without giving details.

Fighter pilot Zhai Zhigang, an unsuccessful candidate for the previous two manned missions, has been touted by the official Xinhua News Agency as the leading astronaut to carry out the spacewalk, expected to last about 40 minutes.

Zhai and fellow astronauts Jing Haipeng and Liu Boming — all three of them 42-year-old fighter pilots — were introduced to journalists at a late Wednesday news conference. A decade of training together ensured effective, smooth cooperation between the three, Liu said.

"The Shenzhou 7 mission marks a historic breakthrough in China's manned space program," Zhai said. "It is a great honor for all three of us to fly the mission, and we are fully prepared for the challenge."