While China has been barred from participation in the International Space Station, mainly over USA objections to the Chinese program's secretive nature and close military connections, it's likely the country would have built its own station anyway as it sought the status of a great space power.
"We experienced some risky situations and encountered some difficulties on that mission", Liu said on Wednesday.
China's space station construction plan calls for a dozen launches, four of them crewed, stretching into 2022.
On Liu's Shenzhou-7 mission in 2008, his first, he nearly did not get to perform a space walk to plant the Chinese flag on the exterior of the spacecraft. Tang, who was recruited as one of the second batch of candidates in 2010, is flying in space for the first time.
The Tiangong space station is to be the third orbiting laboratory launched and operated by China, following the Tiangong-2 station launched in 2016 and de-orbited in 2019, and Tiangong-1 station that launched in 2011 and ceased operation in 2016.
"We're willing to carry out more extensive global exchanges and cooperation with other countries on the issue of debris from spacecraft and in space", Ji said. With China stepping up worldwide cooperation and exchanges, it's only a matter of time before foreign astronauts join the Chinese colleagues on missions to the station, Ji told reporters Wednesday.
"Exploring the vast universe, developing space activities, building a powerful space nation is our unremitting space dream", Ji said.
The mission is the third of 11 planned through next year to add the additional sections to the station and send up crews and supplies.
The astronauts were seen off by space officials, other uniformed military personnel and a crowd of children waving flowers and flags and singing patriotic songs.
While China concedes it arrived late at the space station game, it says its facility is cutting-edge.
Once completed, the station will allow for stays of up to six months, similar to the much larger International Space Station.
Two astronauts on those past missions were women, and while this first station crew is all male, women are expected to be part of future station crews. They'll also be able to bring personal items to remind them of home and stave off boredom while not working, Nie said.
After the Tianhe was launched in April, the rocket that carried it into space made an uncontrolled reentry to Earth, though China dismissed criticism of the potential safety hazard. Usually, discarded rocket stages reenter the atmosphere soon after liftoff, normally over water, and don't go into orbit.
The launch will be carried out with a Long March-2F carrier rocket, which will be filled with propellant on Wednesday morning, Ji said. China published their trajectories and they are expected to burn up long before they could be a danger, he said.