China's Shenzhou XIII mission crew have begun preparations for their scheduled return to Earth in mid-April, according to the China Manned Space Agency.

The agency said on Thursday astronauts Major General Zhai Zhigang, Senior Colonel Wang Yaping and Senior Colonel Ye Guangfu have set the record for the country's longest manned spaceflight and laid a solid foundation for the next steps of the Tiangong space station's in-orbit assembly.

The crew arrived in the Tiangong station on Oct 16, embarking on their six-month journey.

They have carried out two spacewalks, two science lectures and a host of scientific experiments and technology demonstration operations.

Six launches will be made this year to deploy the Shenzhou XIV and XV mission crews to Tiangong station, to transport Tianzhou 4 and 5 robotic cargo spaceships to the station for refueling and resupply operations, and to send two large space labs to dock with the station.

The first of the six to be launched will be Tianzhou 4, which will be followed by the Shenzhou XIV manned spacecraft. Then the two space labs — Wentian, or Quest for the Heavens, and Mengtian, or Dreaming of the Heavens — will be launched into space to complete the station. The fifth to be launched will be Tianzhou 5 and the final will be Shenzhou XV.

Upon its completion at the end of this year, Tiangong will consist of three main components -- a core module attached to two space labs -- and will have a combined weight of nearly metric 70 tons. The station is scheduled to operate for 15 years in a low-Earth orbit about 400 kilometers above the planet.