Tiangong-1 station was never intended to remain in orbit forever. China would eventually stop firing the station’s engines to keep it in a stable orbit, and it would lose altitude until it neared the top of Earth’s atmosphere. China would then carry out what’s known as a controlled reentry. Using quick engine bursts, engineers would guide Tiangong-1 toward a trajectory that would see it fall safely over the ocean. Spacefaring nations often carry out such controlled reentries, for satellites and stations alike.
But in March of 2016, Tiangong-1 mysteriously stopped working. China could no longer command the station to do anything.
In one of the final, dramatic scenes in the 2013 film Gravity (warning: spoilers ahead), Sandra Bullock’s character is stranded alone in a Soyuz capsule, the International Space Station destroyed behind her. After a brief, oxygen-deprived hallucination featuring George Clooney’s character, Bullock maneuvers the Soyuz toward a fictional version of a Tiangong space station and gets in just as the station starts to reenter Earth’s atmosphere.
Bullock’s descent is quite similar to what will happen to Tiangong-1, Muelhaupt says, minus the Steven Price score. Powerful wind streams will buffet the station, shaking it violently. Solar arrays, antennae, and any other protruding hardware will be among the first to snap off.
Before that, it’s possible that Tiangong-1 may hit the top of the atmosphere at such an angle that it could bounce back into space.
“If you put something at a right angle in the air it’s moving through, you can generate some lift. So when an object’s going to naturally decay and reenter and come down into the denser atmosphere, it might generate lift and then come back out again,” Muelhaupt says. “You have to hit the air for reentry at just the right angle.”
Once it makes it into the atmosphere, Tiangong-1 will travel at hypersonic speeds, faster than the speed of sound. “As the thing goes deeper into the reentry, the air piles up in front of it faster than it can get away, and you get this shock wave,” Muelhaupt says. “The molecules in the air literally start coming apart.”
A layer of hot plasma will envelop the space station, and metal will begin to melt from the extreme temperatures. “During that period, where you get this intense heating, if you don’t design a vehicle to survive that heating, it’s going to come apart,” Muelhaupt says. Based on photos China has shared publicly of Tiangong-1, the station does’t appear to have any kind of heat shielding, Muelhaupt says.
Tiangong-1 will break apart into pieces, all of them flying together on the way down, like a flock of mismatched birds. Lighter material will slow down faster and thus experience less heat, which means some of it may survive the fall. Heavier material will experience the most severe heat, but some objects may be so dense that they escape melting before they reach Earth’s surface, too.