Tiangong-1 reentry
A frame from an animaiton depicting Tiangong-1's reentry. The spacecraft reentered late April 1 over the South Pacific. Credit: AGI

WASHINGTON — China’s Tiangong-1 module, whose uncontrolled reentry had been watched with both anticipation and apprehension, returned to Earth harmlessly over the South Pacific Ocean late April 1.

A statement by the U.S. Air Force’s Joint Force Space Component Command (JFSCC) at Vandenberg Air Force Base in California said that the spacecraft reentered at approximately 8:16 p.m. Eastern April 1 over the South Pacific, far from any inhabited landmasses. There were no immediate reports of anyone, on land, at sea or on aircraft, witnessing the reentry.

Chinese officials also reported that the spacecraft reentered at approximately 8:15 p.m. Eastern, according to a statement from the China Manned Space Engineering Office. While the U.S. Air Force statement was based on data from its Space Surveillance Network, it wasn’t clear how China, with far fewer assets to track space objects, pinpointed the reentry time.

In its statement, JFSCC suggested, but did not explicitly state, that it was sharing information about Tiangong-1’s orbit with China. “All nations benefit from a safe, stable, sustainable, and secure space domain,” said Maj. Gen. Stephen Whiting, deputy commander of JFSCC, in the statement. “We’re sharing information with spacefaring nations to preserve the space domain for the future of mankind.”

The reentry location is not far from an area of the South Pacific used for deliberate reentries of spacecraft, such as International Space Station cargo spacecraft. However, China had lost control of Tiangong-1 long before the reentry, causing some concern about an uncontrolled reentry of the 8.5-ton spacecraft, pieces of which were expected to reach the surface.

Predictions in the last week had narrowed the likely reentry time to March 31 or April 1, but with errors bars too large to pinpoint a reentry location. That reentry time drifted to late April 1 because low solar activity had reduced the amount of atmospheric drag on the spacecraft. The actual reentry matched several final predictions by organizations such as The Aerospace Corporation and the European Space Agency, which still had error bars of a few hours.

China launched Tiangong-1 in September 2011 to test technologies intended for a future space station. An uncrewed Shenzhou spacecraft, Shenzhou-8, docked with Tiangong-1 in November 2011. It was followed by two crewed missions: Shenzhou-9, which spent about 10 days docked with the module in June 2012; and Shenzhou-10, which spent 12 days at Tiangong-1 a year later.

While no spacecraft visited Tiangong-1 after the Shenzhou-10 mission, China continued to operate the spacecraft remotely to monitor its performance. While original plans called for a controlled reentry of the module at the end of the mission, Chinese officials reported in 2016 that it ended communications with Tiangong-1.

China launched a second, similar module, Tiangong-2, in September 2016. The two-person Shenzhou-11 crew spent a month docked to the module in October and November 2016, the only crewed mission to visit that module to date. A prototype cargo spacecraft, Tianzhou-1, launched in April 2017 and performed a series of docking tests with Tiangong-2 through September 2017.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...