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The Tiangong-1 or ‘Heavenly Palace’ will mostly burn up in the atmostphere but there’s a chance that a ‘significant’ portion will survive.
The Tiangong-1 or ‘Heavenly Palace’ will mostly burn up in the atmostphere but there’s a chance that a ‘significant’ portion will survive. Photograph: Shutterstock/Rex
The Tiangong-1 or ‘Heavenly Palace’ will mostly burn up in the atmostphere but there’s a chance that a ‘significant’ portion will survive. Photograph: Shutterstock/Rex

Where will the out-of-control Chinese space station land?

This article is more than 7 years old

Scientists have admitted that they have no way of safely guiding Tiangong-1 back to Earth, and say it is moving too fast to accurately predict where debris from the 8.5-tonne module will crash

What is happening with the Chinese space station?

The nation’s first prototype space station, Tiangong-1, or “Heavenly Palace”, launched into orbit in September 2011. The module reached the end of its service life earlier this year and was due to splashdown – eventually – in the Pacific Ocean. But at a recent press conference, the Chinese space agency admitted it had lost contact with the station. They did not explain what had gone wrong.

Does losing contact matter?

It depends what the Chinese planned to do next. If the agency was going to let the spacecraft simply fall to Earth in an uncontrolled way and burn up in the atmosphere, then the loss of contact means little. But if they had intended to perform a controlled de-orbit, that option is now gone. Controlled de-orbits tend to be reserved for spacecraft that pose a potential risk to people when they fall back to Earth. If the chances of someone being injured by components that survive the fireball of re-entry is greater than one in 10,000, then the spacecraft should be actively steered into a region of the South Pacific known in the business as the “spacecraft graveyard”. The module is already below the altitude of the International Space Station (ISS) and so there is no risk of a collision on its way down.

What was Tiangong-1 for?

Unlike the massive ISS, which is the size of a football field and has the living space of a five-bedroom house, Tiangong-1 is a mere 10 metres long and 3 metres wide. The Chinese used the module to practise rendezvous and docking procedures, and several taikonauts, including two women, spent time aboard after catching a ride on the Shenzhou spacecraft. Losing control of the module is more of an embarrassment to the Chinese space agency than a blow to their space programme. Two weeks ago, in a long-scheduled launch, the Chinese put another space station module, Tiangong-2, into orbit, and a crew of at least two taikonauts is expected to visit as early as next month. The agency still hopes to build a 55-tonne space station by 2020.

Will the stricken module survive re-entry?

Satellite tracking radar show the Chinese module at 380km high and travelling at 27,500km per hour. At that speed and altitude, it could lap the planet 5,000 more times before it starts to feel the drag of the upper atmosphere and begin its final descent. Most of the 8.5-tonne module will burn up from aerodynamic heating in the Earth’s atmosphere. But the Chinese space agency has conceded that some heat-resistant components may survive. “The module is predominantly a hollow shell, so there’s a good chance a significant portion will burn up in the atmosphere. But there’s also a chance some elements will survive down to surface,” said Hugh Lewis, a space debris expert at University of Southampton.

Where will it come down?

No one knows. And the vagaries of re-entry mean it will be impossible to predict with accuracy, even in its final moments. Computer simulations cannot tell far in advance on which orbit a spacecraft will re-enter. The Tiangong-1 is moving fast, at a shallow angle relative to the atmosphere, and the height of the atmosphere at any point depends on the regional temperature. But even when an object has begun its descent through the atmosphere, the final resting place of debris is still hard to predict. How the spacecraft tumbles through the atmosphere has an influence on how it breaks up. The most space agencies can do is calculate a debris ellipse where fragments are expected to land.

Are we in danger?

Pieces of space debris fall to Earth every day, but most of these are small fragments. Now and again, whole satellites or rocket stages tumble out of orbit and break apart in the sky. The most dangerous uncontrolled re-entry happened in 1979 when Nasa’s 85-tonne Skylab space station came down over Australia. In 2001, when the Russian Mir space station had reached the end of its life, Roscosmos de-orbited the 135-tonne outpost into the Pacific. But even with so much hardware raining from the skies, no one is known to have been hurt by falling space junk. “It is luck, but it proves that luck is on our side,” said Lewis. The odds are wildly in favour of not being hit because most of the Earth’s surface is covered with water, and most of the world’s population is crammed into a small percentage of land. The chances of a specific individual being struck by falling debris is trillions to one, making death by lightning far more likely.

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