A rendering of the Tiangong-1 space lab in orbit.
TIANGONG-1 REENTRY UPDATES
Latest reentry forecast provided by ESA’s Space Debris Office, ESOC, Darmstadt, Germany.
Update 6 March 2018
The current estimated window is ~29 March to ~9 April; this is highly variable.
Reentry will take place anywhere between 43ºN and 43ºS (e.g. Spain, France, Portugal, Greece, etc.). Areas outside of these latitudes can be excluded. At no time will a precise time/location prediction from ESA be possible. This forecast will be updated approximately every week in January and February.
Tiangong-1: ESA reentry window estimate narrows to March 30-April 6
European Space Agency scientists tracking the orbit of China's Tiangong-1 space lab have released a new estimate for atmospheric reentry of between March 30 and April 6.
The estimate from ESA's Space Debris Office for March 15 states that the window is highly variable, due to the complexities of modelling the atmosphere, the dynamics of the reentering object and limitations in observing the spacecraft.
China's 8-metric-tonne Tiangong-1 space lab was launched in 2011 and used to test docking technology with the uncrewed Shenzhou-8 spacecraft shortly after.
It later tested life support systems by hosting two crews from the Shenzhou-9 and Shenzhou-10 missions in 2012 and 2013, acting as a stepping stone to an eventual large, modular Chinese Space Station.
The crewed Shenzhou-10 spacecraft docking with Tiangong-1 space lab in June 2013.
In 2016, it became apparent that the orbit of the spacecraft could not be changed and it would eventually make an uncontrolled atmospheric reentry.
ESA's Space Debris Office, based at the ESOC mission control centre in Darmstadt, Germany, has been tracking the orbit of Tiangong-1 and posting regular updates on its orbital status during 2018.
Tiangong-1 is currently orbiting with a perigee, or closest point to the Earth during orbit, of 224 km and apogee, or farthest point, of 246 km, according to USSTRATCOM's Joint Space Operations Center, which detects, tracks and identifies all artificial objects in Earth orbit and provides daily updates.
The space lab had a perigee of 235 km and apogee of 257 km on March 8. The decay of Tiangong-1's orbit, which is caused by atmospheric drag, is accelerating as the spacecraft runs into increasingly denser concentrations of particles at lower altitudes.
Tiangong-1 reentry window forecast by ESA's Space Debris Office as of 15 March, 2018.
The Aerospace Corporation, which is also following the situation, estimating that Tiangong-1 will reenter the Earth’s atmosphere around April 4th, 2018 plus or minus one week, in a March 15 update.
The last note issued by China to the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), in December, had a predicted window from the first 10 days of February to the last 10 days of March.
Chinese astronaut Wang Yaping during a live science lecture to school classrooms from orbit aboard Tiangong-1 in July 2013.
Tiangong-1 orbit and deorbiting
It was initially assumed that China would deorbit Tiangong-1 in a controlled manner, as with Tianzhou-1, using the same propulsion systems it used to regularly raise its orbit. However, in early 2016, China lost telemetry from the space lab, meaning the craft will come down randomly.
The orbit of Tiangong-1 carries it over the Earth between 43 degrees North to 43 degrees South, meaning as far south as southern Chile and Argentina, and a little farther north than New York and Chicago in the US and Rome in Italy.
Most of the craft will burn up on reentry, but anything that does not burn up could land at any point within this zone. Remaining debris is considered highly unlikely to pose a threat to people or infrastructure.
Despite the low probability of causing harm or damage, the fate of Tiangong-1 has attracted wide attention, with the Verge noting the role of humans having a bad grasp of probability and risk assessment.
Should the reentry occur over populated areas, it could put on a light show, as with a spent stage of a Long March 7 rocket over the United States in June 2016.
Any debris could, however, be contaminated with the remaining toxic and carcinogenic hypergolic fuel carried by the space lab as propellant.
The Chinese notification to the UN claims that the methylhydrazine and dinitrogen tetroxide propellant used by Tiangong-1 burned and destroyed along with its structural components during the course of re-entry.
For more, ESA has an FAQ on Tiangong-1 reentry which can be found here.
Long March 7 rocket stage burns up on reentry.
Towards a Chinese Space Station
While Tiangong-1 is doomed to suffer a fiery fate in the next few weeks, the later Tiangong-2, launched in 2016, is continuing its work in low Earth orbit after playing a role of a stepping stone towards a large, modular space station.
Tianhe will be the CSS core module, and includes living quarters for astronauts. It will be joined by two science modules and orbit an altitude of around 390 kilometres above the Earth for around 10 years, carrying three astronauts for 3-6 months at a time.
A rendering of the completed Chinese Space Station, including docked Shenzhou and Tianzhou spacecraft.
A Chinese Space Lab Will Soon Fall From The Sky. Where It Lands, No One Knows
A model of the Tiangong-1 space station at a Chinese airshow in 2010. The real Tiangong-1 will reenter the atmosphere around the end of March.
A Chinese space lab the size of a city bus will soon be falling back to Earth, and no one knows exactly where bits of it might crash down.
Current predictions say that the 19,000-pound lab should re-enter the earth's atmosphere sometime in the last few days of March or the first few days of April.
The lab is called Tiangong-1, which means "heavenly palace." China launched it into space in 2011. The outpost was briefly visited twice by Chinese taikonauts, including Wang Yaping, who beamed down a science lecture to schoolchildren.
Although Tiangong-1 has been called a Chinese "space station," it actually is just a precursor to China's planned space station, says Joan Johnson-Freese, a professor at the Naval War College.
Since 1992, she says, China has been following a methodical program "to demonstrate human space flight and culminate with a large space station."
For that, China's space agency needs to get experience with things like docking and long-term life support in space. Tiangong-1 and another lab in orbit called Tiangong-2, "have been technology test bed laboratories to do experimentation on all those different areas and more," she explains.
Now, though, Tiangong-1 is headed back down. And even though space junk this size falls to Earth a few times a year, it's usually something like a spent rocket stage — not a home-away-from-home for space travelers.
"These kinds of events are noteworthy and people in this business kind of watch to see what they can learn about how these things come apart as they come down," says Bill Ailor of the Aerospace Corporation's Center for Orbital and Reentry Debris Studies.
Most of it, though not all, should burn up during the fiery re-entry.
"Somewhere between, say, 2,000 and 8,000 pounds might come down," Ailor says.
The possible impact zone covers about two-thirds of the globe, including a lot of the continental United States. But exactly where and when is hard to predict because the vehicle will interact with the atmosphere, which is constantly changing.
Still, don't worry about getting hit, says Ailor. "It's just not a very likely event that a particular person would have a problem with it," he says.
In 60 years of space exploration, only one person — an American woman named Lottie Williams — is known to have been struck by falling space junk, says Ailor, "and it was just like a piece of fabric material that kind of brushed her on the shoulder."
He hopes that someone gets to see the bright streaks created by Tiangong-1 breaking up and burning.
"It would be a beautiful thing to watch," says Ailor.
But since most of our planet is covered by oceans, he says the most likely scenario is that it will come down over the water and never be seen or heard from again.