Chinese Space Station Due to Return to Earth
- 20th Mar 2018
- Author: Tamela Maciel
Better keep a watchful eye on the skies over the next few weeks.
China’s abandoned space station, Tiangong-1, is due to re-enter Earth’s atmosphere any time between 30 March and 6 April – and some of it may even hit the ground.
UPDATE: The estimated window of reentry is now 30 March to 2 April.
Luckily, the chances of this debris striking an inhabited area are slim, and the entire UK is off the hook as it is too far north.
Tiangong-1
China launched its first space station, Tiangong-1 or “Heavenly Palace”, back in 2011. It was visited by astronauts in 2012 and 2013, but since then it has been dormant in orbit, replaced by a more advanced station, Tiangong-2.
In March 2016 China lost contact Tiangong-1. This meant that the station could no longer be controlled in orbit.
Like many other satellites in low-Earth orbit, Tiangong-1 feels a slight drag from the residual atmosphere of Earth at 250 kilometres up. Without the commands from ground control to boost its speed occasionally, this space station must eventually fall out of orbit and re-enter Earth’s atmosphere. China confirmed this back in September 2016, and now that time for re-entry has come.
Orbital mechanics combined with atmospheric drag is a notoriously imprecise science – especially when the object in question is a 12-metre-long cylinder with large solar panels. It’s not exactly an easy calculation to estimate when and where Tiangong-1 might land (if at all), since it all depends on the exact conditions of the atmosphere and the angle of entry, to name just a few factors.
These days, most satellites that reach the end of their life are either sent to a far-off ‘graveyard orbit’ so that they aren’t a risk to active satellites, or else they are carefully controlled during re-entry so that they land over an empty region of the south Pacific ocean. Unfortunately, Tiangong-1 is beyond control and the Chinese space agency can’t guarantee that part of it won’t hit land.
Luckily the Earth is mostly ocean and mostly uninhabited. So the chance of a bit of Tiangong-1 debris causing harm to humans is extremely small. In the history of spaceflight, there have been no casualties from falling space debris.
Nevertheless, the world will be keeping a wary eye to the sky over the next few weeks. The European Space Agency’s Space Debris Office estimates that Tiangong-1 will fall out of orbit between 30 March and 2 April, with this window due to narrow closer to time.
Because of the orbit of Tiangong-1, it can only fall in locations between 43o north and 43o south. This let’s the British Isles, northern Canada, northern Europe, and Russia off the hook, but it’s nevertheless a huge area that includes the United States, most of South America, southern Europe, Africa, southern Asia, and Australia.
Re-entry modelling is extremely difficult and imprecise! But just to reiterate, it’s highly unlikely that any debris will fall on a populated area.
Historic Crash and Burns
Other space stations have de-orbited in similar fashions in the past. In 1979, the US space station, Skylab, fell out of orbit in an uncontrolled re-entry. Debris landed in Western Australia in a (luckily!) uninhabited region.
The Soviet space station Salyut 7 deorbited in 1991 and rained debris over Argentina.
Finally, this week marks the 17th anniversary of the deorbit of Russia’s Mir space station, carefully deorbited over an empty section of the south Pacific.
About the author: Dr Tamela Maciel is the Space Communications Manager at the National Space Centre
