Yesterday's headlines about the Chinese space module Tiangong-1 were a bit alarming, to say the least, claiming the eight-ton craft was "in freefall," "hurtling towards Earth" and would "rain molten metal down onto Earth." So we'd like to say: Please don't panic.
Not only is it much too soon to tell whether Tiangong-1 is out of control, but there is little reason to worry about it falling out of the sky, astrophysicist Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics tells Smithsonian.com. “In the history of the Space Age, uncontrolled re-entries have been common,” he says. “And the chance that debris from any one of them hits somebody, it’s one in thousands.”
The concerns over Tiangong-1’s fate stem from two main sources: a press release the Chinese government published earlier this year and amateur astronomer observations, reports Miriam Kramer at Mashable.
Back in March, The Chinese Manned Space Engineering office (CMSE) announced that the space agency had terminated its data link with Tiangong-1 and would monitor its orbit as it descends into the Earth’s atmosphere and burns up, the state-run news agency Xinhua reported at the time. But because the release didn’t explicitly state that the CMSE was in control of Tiangong-1, some misinterpreted it as a sign that all was not well at mission control. In the meantime, amateur astronomers reported witnessing the space lab flicker as it orbited Earth, which some took as evidence that the station was spinning out of control.
First, there is no indication that the station is out of control. Though the flickering may be a sign that the module is spinning, that doesn't mean it's in a death spiral. Second, terminating the data link is not evidence of certain death, it just means that they are no longer using the module to collect data, says McDowell. They can also reestablish communication in the future, if necessary. McDowell speculates that CMSE is putting the module into hibernation until after its replacement, Tiangong-2, launches. But the Chinese government's reticence on the matter has further magnified all rumors.
In the unlikely event that Tiangong-1 is out of control, there is no reason to look up at the skies in fear of falling space stations, he says. The odds are that pieces that do make it through will land in either ocean or unpopulated regions. In fact, SpaceLab, a craft ten times the size of Tiangong-1, reentered the atmosphere in 1979 and most of it went up in flames over western Australia.
“Last year, a couple of farmers in Spain found these metal spheres in their fields,” McDowell says. “That was probably from a two-ton rocket stage left in orbit. It didn’t even make the news at the time.”
Currently, Tiangong-1 is orbiting at about 215 miles above the ground—a relatively low altitude for an orbital satellite. That makes it easy to spot and could account for some of the worry among amateur astronomers who have noted changes in its appearance. But not only has Tiangong-1 been at this low altitude before, so has the International Space Station (ISS).
Despite recent stories, China's Tiangong-1 spacelab is not about to reenter. Let's see if it reboosts or not by 2017 pic.twitter.com/VcF93MLgHT— Jonathan McDowell (@planet4589) July 12, 2016
Since the ISS and Tiangong-1 both have relatively low orbits, they experience slight drag from the Earth’s atmosphere that causes them to lose altitude over time, McDowell says. But the engineers for both crafts developed ways to ensure they don't fall too low in the sky. The ISS relies on its regular vistors to nudge it back into higher orbit. "They fire their engines and give it a boost," McDowell explains. But Tiangong-1 doesn't receive quite as many visitors and is much smaller, making it more effective for the CMSE to periodicly reposition the space lab using the onboard engine.
Even in the worst circumstances, the space station wouldn’t enter the atmosphere until at least 2017. And reentry isn't something to be feared. “Most likely, some people will see a nice re-entry like a meteor overhead,” McDowell says. “If this were the day Tiangong-1 was re-entering, it still wouldn’t be high on my list to worry about.”