China's joint assembly of the unmanned spacecraft Shenzhou 8 and the prototype space lab Tiangong-1 at 12:04 p.m. Tuesday Beijing Time carried out orbit maintenance for the second time, according to the mission's control center.

While on Monday China completed its second space docking test during which the spacecraft Shenzhou-8 disengaged from Tiangong-1 module after an around 12-day flight together and then re-docked with it.

Shenzhou 8, launched on Nov. 1, rendezvoused and docked with the target orbiter Tiangong-1 on Nov. 3 in an orbit 343 km above Earth. Tiangong-1 has been in orbit since its launch on Sept. 29.

The coupled spacecraft performed their initial orbit maintenance successfully on Nov. 4, and Tuesday's maintenance is their last such operation before Shenzhou-8's return to Earth, according to Beijing Aerospace Control Center (BACC), which is in command of the mission.

Shenzhou-8 is set to return to Earth Thursday evening, Wu Ping, spokeswoman for China's manned space program, said earlier.

Tang Geshi, a scientist with the BACC, said the joint spacecraft reached the designated orbit after the most recent orbit maintenance and then their flight path was readjusted at 4:59 p.m. Tuesday, in order to prepare for Shenzhou 8's return to Earth.

Shenzhou-8 is expected to perform an orbit maintenance operation after its disengagement from Tiangong-1, so as to keep itself orbiting at a height of 343 km above Earth as it signals to return to Earth, Tang said.

Tang said the next orbit maintenance will also help ensure Shenzhou 8 lands back in the designated area on Earth.

Two docking missions with Tiangong-1 have been planned next year, and at least one will be manned, according to Wu. China plans to establish its own space lab around 2016 and a manned space station around 2020, she said.