With the launch of the U.S. Space Force, this thread might become relevant again.

TECH & SCIENCE
TIANGONG-2: CHINA'S NEW SPACE STATION UNEXPECTEDLY DIVES TOWARD EARTH, BAFFLING EXPERTS
BY ARISTOS GEORGIOU ON 6/25/18 AT 12:38 PM

China’s Tiangong-1 space station caused a sensation earlier this year when it crashed to Earth in an uncontrolled fireball. Now, its successor, Tiangong-2, has been displaying some strange behavior, which has left experts puzzled.

On June 13, the spacecraft unexpectedly dropped from its usual orbit of 242 miles to 183 miles before returning to its original position, according to Jonathan McDowell, an astronomer from the Harvard-Smithsonian Center for Astrophysics who examined new data from the U.S. Strategic Command’s Joint Force Space Component Command.

He tweeted: “OK now that's weird. New orbit data for Tiangong 2 shows it back in the 390 km orbit after spending 10 days in the lower 295 km orbit. Wonder what that was about??”

Jonathan McDowell
✔
@planet4589
23 Jun
OK now that's weird. New orbit data for Tiangong 2 shows it back in the 390 km orbit after spending 10 days in the lower 295 km orbit. Wonder what that was about??

Jonathan McDowell
✔
@planet4589
My best fit to the data is that TG-2 reboosted at 0117 and 0202 UTC Jun 22, for a total delta-V of 56 m/s and a propellant usage of about 144 kg.

12:59 PM - Jun 23, 2018
20
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McDowell speculated that the unexplained maneuver is an indication that Chinese space authorities are planning to de-orbit the space station in a more controlled manner than its predecessor.

"Possibly just testing out the spacelab's engine reliability after 2 years in orbit, as part of end-of-life tests?" he wrote.

Phil Clark, an expert in China’s space activities, told SpaceNews that: “In part China doesn’t want a repeat of Tiangong-1 going rogue.”

The older space station suffered a malfunction in early 2016 that led to a loss of contact with operators on the ground. While most of it burned up during re-entry, with the surviving debris landing harmlessly in the Pacific, the spaceraft’s demise was widely publicized.


China's Tiangong-2 space lab is launched on a Long March-2F rocket from the Jiuquan Satellite Launch Center in the Gobi Desert, in China's Gansu province, on September 15, 2016.
AFP/GETTY IMAGES

Tiangong-2, which measures 10.4 meters long and weighs 8.6 tons, was launched in 2016. It was designed as a test environment for technologies that will be used on China’s upcoming modular space station, known as Tianhe, which will be much larger, weighing up to 100 tons.

Tiangong-2’s propulsion system could be the same as the one Tianhe is set to have, according to McDowell, leading him to suggest that the latest maneuver was conducted in order to gather valuable data on this.