China’s second space lab dived unexpectedly toward Earth this month, just two months after its predecessor crashed uncontrolled into our planet’s atmosphere.

Tiangong-2 took an unexpected dive of about 59 miles (95 kilometers) two weeks ago but again rose up to its previous position which was 242-mile-high (390 km) orbit on June 22, as explained by Jonathan McDowell who works as an astronomer at the Harvard-Smithsonian Center for Astrophysics. McDowell has been keeping an eye on the exciting things revolving around the Earth.

McDowell said that the first dip suggested that China may be preparing to take down Tiangong-2 from the orbit, but the rise back up to 242 miles indicated some other happening. (The evidence of these maneuvers comes from tracking data gathered by the U.S. government.)

This might be China’s regular exercise to examine the subsystems aboard Tiangong-2, which was launched in September in 2016. McDowell deducted that these subsystems may be incorporated in the space stations China plans to build in Earth orbit by 2022.

He told reporters that China likely “want more baseline on how the propulsion system works, how reliable it is, how well it works after two years in space.”

Observers are not sure when the re-entry of Tiangong will occur. But McDowell said that China has enough control over the vehicle to conduct a directed de-orbiting process if need may be.

Concerns existed because China’s previous Tiangong-1 had crashed uncontrollably in the planet’s atmosphere. It was launched in September 2011and hosted two visiting astronaut crews, in June 2012 and June 2013. Communication between Tiangong-1 and the team was disrupted in March 2016, causing the massive craft to dip into the atmosphere on April 1 this year. It broke apart and burnt over the southern Pacific Ocean.

Fortunately, the re-entry of Tiangong-1 caused no injury or damage to anything. And by surprise, it came back to Earth near “Point Nemo,” which is an isolated area of water where mission planners try to ditch their spacecraft under certain circumstances. 

China launched both the Tiangong crafts in the light of building a full-on space station. Tiangong-2 hosted one set of astronauts, in October-November 2016, and served as the base for multiple robotic refueling demonstrations, the last of which wrapped up in September 2017.

Though China managed to control the spacecraft this time, McDowell said it should not be taken for granted.