China’s Tiangong-1 space station will make an uncontrolled re-entry into the Earth’s atmosphere within weeks, and while most of the 8.5 tonne module will burn up, experts say large chunks may survive to rain down on the surface.
The good news? The odds are in your favour.
Tiangong-1 (“Heavenly Palace 1”) is China’s first space station and was active from September 2011 to December 2015. The initial plan was to de-orbit it in 2013 by carefully firing its engines, allowing it to burn up in the atmosphere over a largely unpopulated area of the southern Pacific Ocean. However, priorities changed.
Then in 2016 Chinese ground teams lost control of the space station. Its orbit is now decaying and it is expected to re-enter the atmosphere sometime around April 3. Friction will generate extreme amounts of heat and disintegrate most of the craft, making it visible from some locations for tens of seconds, like a fireball.
According to Michael Smart, hypersonic aerodynamics researcher at the University of Queensland, Australia, it is difficult to predict how the space station will break up and what will survive the fiery journey.
“For an object with a smooth well-defined shape and made of known materials, it is relatively easy to calculate where it will land and how much will be left,” he explains.
“For a large complex flexible object like a space station it is very difficult to predict. There will be a large uncertainty.”
Duncan Steel, a British space scientist with extensive experience in the aerospace sector, including research stints at the NASA-Ames research centre in California, expects a few of the strongest, densest parts to fall to Earth intact.
“Such surviving bits would have been slowed down and would fall vertically and hit the surface at much the same speed as if they had been dropped from a jetliner,” he says.
This is about 300 kilometres per hour.
Where these pieces will end up depends on the variable conditions in the very high atmosphere. Chances of impact are higher in parts of Europe, US, Australia and New Zealand.
But Steel stresses that there is no cause for alarm. Three quarters of the globe is covered in water, after all, and humans are spread relatively sparsely across the remaining quarter. According to a statement recently released by the US-funded Aerospace Corporation, you are a million times more likely to win the Powerball jackpot than to have a piece of debris from Tiangong-1 crash down on your head.
The statement points out that in the history of spaceflight, “only one person has ever been recorded as being hit by a piece of space debris and, fortunately, she was not injured”.
Even if the debris does no damage upon impact, it still may contain traces of hydrazine, a highly toxic and corrosive substance that Tiangong-1 used as engine fuel. {%recommended 448%}
In a statement made via the UN’s Committee on Peaceful Uses of Outer Space (UNCOPUOS) in December 2017, China maintained that the fuel would burn up on re-entry and not pose a danger. However, Aerospace strongly recommends not to touch any debris or inhale vapours from it.
This event raises questions about the ethical and legal responsibilities of space agencies. Thousands more pieces of space junk remain in slowly-decaying orbits around the Earth, from defunct satellites to dropped astronaut tools.
Kim Ellis, space law expert and director of Australian company International Earth & Space Technology, notes that since China is a member of UNCOPUOS and a signatory to the Outer Space Treaty, it has a legal responsibility “to ensure any space vehicle or object, from beginning to end of its life, does not cause damage to either people or property on Earth and in space”.
Ellis explains that China is liable to pay compensation for damage caused by Tiangong-1 or its components, either on the surface of the Earth, to people and property, or to an aircraft in flight.
The Chinese station is not the only — or even the biggest — uncontrolled spacecraft to crash back down to Earth. This title is held by NASA’s 74-tonne Skylab space station, which memorably scattered debris near the town of Esperance in Western Australia in 1979. Tongue-in-cheek, the shire council fined NASA $400 for littering, an amount that was eventually paid in 2009 by California radio DJ Scott Barley and his listeners.
To avoid future hail-storms of debris, Smart suggests that large structures “should be broken into more manageable pieces in orbit, so that less mass reaches the surface and it’s easier to predict where they will go”.
Steel adds that the safest option is to ensure that large defunct objects in low Earth orbit are guided into a controlled re-entry of the Earth’s atmosphere over oceans.
Smart hopes that this event will not influence the public’s opinion on establishing a space agency in Australia. “This is part of ‘old space’,” he says. “The new Australian Space Agency will hopefully be all about ‘new space’ where environmental concerns are taken into account.”