China's Shenzhou VI space capsule fired rockets Friday morning to tweak its trajectory during a 30th orbit of Earth, a correction that state media described as routine and planned even before lift-off.
The operation, carried out shortly before 6 am Beijing time (2200 GMT Thursday), took just a few seconds to restore the vessel to its original trajectory, Xinhua news agency said, citing information from the Beijing Aerospace Command and Control Centre.
"Under influence of the Earth's atmosphere and gravity, the spacecraft's orbit will gradually drop," Xinhua said, adding that engineers had planned to make a minor course change after 30 orbits.
The tweak boosted the spacecraft's altitude by 800 metres (2,625 ft), the state-run People's Daily said on its Web site, www.people.com.cn.
Xinhua said another "orbit maintenance operation" was scheduled for the mission's 61st orbit.
The Shenzhou VI blasted off smoothly on Wednesday morning, carrying China's second and third men into space two years after its first manned mission.
On Thursday, astronauts Fei Junlong and Nie Haisheng busied themselves by exaggerating their movements while opening and closing internal doors, changing out of their spacesuits and using equipment to test the effects on the craft's movement.
"The results proved that the spacecraft was fully capable of enduring all the disturbances, and then astronauts would be allowed to move in a relatively free way," Zheng Songhui, a consultant for the spacecraft's systems, was quoted as saying.
Though expected to stay in space for five days, the exact time of the Shenzhou VI's return to Earth would depend on the weather and other conditions around the main landing area in a remote part of China's grassy Inner Mongolia region, Xinhua said.
It could come back before or after its planned Monday touch-down, Wu Guoting, from the China Research Institute of Space Technology, was quoted as saying.
"The spacecraft has been well prepared for a longer journey, with supply of food, oxygen, water and other necessities enough for a seven-day space flight," Wu added.
Authorities have already warned nomads and herdsmen living near the landing area to be on the lookout for falling objects.