China's third manned space mission, Shenzhou-7, shoulders four major tasks, including the country's first attempt on space walk, chief designer of the country's manned space program Zhou Jianping said on Thursday.

"The space walk is an important step of China's manned space program," Zhou told Xinhua at Jiuquan Satellite Launch Center in northwest China before the launch of Shenzhou-7.

Manned space program involves three basic technologies, including the launch and return of astronauts, extravehicular activities (or known as space walk) and docking of orbiters.

China has announced that its manned space program is being carried out in three stages, which eventually lead to the establishment of a permanent space station.

In the first stage of the program, China has sent unmanned spacecraft and a manned spacecraft into near-earth orbit, conducting observations of the earth and scientific experiments in space, and bringing back the astronaut safely to the earth.

The planned space walk during the Shenzhou-7 mission will be one key step of the program's second stage, which also involves the docking between capsule and space module and establishment of a space lab.

In the third stage, China will build a permanent space laboratory and a space engineering system. Astronauts and scientists will travel between the earth and the space station to conduct scientific experiments of larger scale.

Other tasks of the Shenzhou-7 mission included the test of solid lubricant and plates of solar battery in the outer space, Zhou said.

"Astronaut will take the materials placed outside the capsule back to the orbital module," Zhou said, adding that scientists hoped to improve the property and lifetime of the materials by studying the samples.

Solid lubricant is widely used in spacecraft. The test sample carried by Shenzhou-7 include 11 types of solid lubricants.

Zhou said the third task of the Shenzhou-7 was the release of a small monitoring satellite, which would orbit the orbital module.

"The task will test our ability to observe and control two satellites in relative motion," Zhou said.

The small satellite, weights less than 40 kilograms, will send back video images of the orbital module.

The fourth task was the trial of data relay. "The completion of the task would greatly improve the coverage and efficiency of our observation network," Zhou said.

The Shenzhou-7 spacecraft, with three astronauts on board, blasted off from the Jiuquan launch center at 9:10 PM on Thursday.

(Xinhua News Agency September 26, 2008)