China’s First Space Lab Tiangong 2 Reentered Atmosphere in a Controlled Manner

China’s space lab Tiangong 2 successfully de-orbited and reentered the atmosphere in a controlled manner on July 19 after operating 1,036 days in space.A small amount of debris fell into a preset safety area in the South Pacific Ocean.

“The Tiangong 2 space lab not only has carried out all planned and extension tasks perfectly,it has finally drawn to a successful end of its mission by de-orbiting in an active controlled manner,’ ZHU Zongpeng,Chief Designer of the space lab said.

ZHU stated that the Tiangong 2 space lab had a designed on-orbit operation lifetime of 2 years and had operated in space for more than 1000 days.Although the space lab had been operating longer than its designed lifetime for nearly one year,the platform and payloads onboard it functioned well and were in good condition with sufficient propellant for supporting its on-orbit operation for several years.“Considering the on-orbit reliability and safety,we have to de-orbit the space lab actively,”ZHU said.

ZHU Zongpeng said that with the increase of the extended time,the on-orbit reliability of Tiangong 2 would decrease.Once it was in abnormal orbit,the uncontrolled Tiangong 2 in near Earth orbit would descend gradually and a little debris could drop to the ground due to incomplete ablation of some high melting point materials as it reentered atmosphere and pose great risk to the safety of the people.Hence China took the responsibility as a major power by deorbiting Tiangong 2 when it was still in good condition to ensure 100% percent safety.

The controlled deorbit enabled Tiangong 2 to land in the designated area at the scheduled time to ensure the safety at ground level,ZHU introduced.This was the second controlled deorbit of China’s spacecraft.Different from the first deorbit mission of Tiangong 1,Tiangong 2 used a two-step flight control implementation strategy.The first step was to reduce the orbit of Tiangong 2 to an elliptical orbit with a perigee of 200 km and the second step was to reduce the orbit again to a 70 km perigee orbit and entered the atmosphere.In order to fully and completely collect all types of active deorbit data of the spacecraft and master orbital characteristics,the Tiangong 2 team did not use the matured technology used before.

The controlled deorbit of Tiangong 2 has great significance.There are over 20,000 space debris over 10 cm in size.In general,any sort of impact with space debris over 10 cm would be catastrophic for spacecraft in space,which often have to change orbits and avoid obstacles to ensure their own safety. It is very difficult to deal with space junk.It needs over 10 years for space debris at 400 km near Earth orbit to fall into Earth's atmosphere and incinerate naturally.Thousands of spacecraft float in the medium-and high-Earth orbits might be obstacles for ever if not be destroyed actively.

Artist's concept of Tiangong 2

The controlled deorbit of Tiangong 2 provided data for promoting active deorbit technology in China.Spacecraft consume a lot of fuel during the deorbit process due to attitude and speed adjustments.If the controlled deorbit option can be optimized continuously and reduce fuel consumption as much as possible,it has great practical value for spacecraft in mediumand high-Earth orbits and is of major importance in exploring an economical,harmonious and environmentally friendly way for the space industry.

During its operation in space,Tiangong 2 had conducted multiple rendezvous and dockings with the Shenzhou 11 manned spaceship and the Tianzhou 1 cargo ship while making a series of space experiments,demonstrated technologies including astronaut medium-term stay and propellant in-orbit refueling.Tiangong 2 had played a significant role in the development of China’s manned spaceflight and laid a sound foundation for building the space station.

The R&D team from CAST simulated the operational state of a space station to make high frequency compressor life tests and a series of extension tests including active orbit descent control.Tiangong 2 which was in good condition is of great significance when considering space station construction.In addition,Tiangong 2 carried 14 application payloads of nearly 600 kg,including a space cold atomic clock,a wide-band imaging spectrometer and a three-dimensional imaging microwave altimeter which involve several technology areas including space physics,Earth science observation and space science experiments.Tiangong 2 has played a critical role in supporting space application tests conducted for various devices in space which would bring huge economic and social benefits.(GUO Zhaowei/BAO Shi/China Space News)