EXPERT REACTION: Chinese Tiangong-1 space station coming in for a fiery landing

UNSW Canberra Space is conducting research to characterise and predict the motion of objects in Earth orbit. As part of this effort, we are currently conducting a study using telescopes to collect images of different space objects in order to gain information about their size, shape, orientation, and orbit.

Three years ago, we successfully collected several images of the Tiangong-1 space station as it was docking with the Shenzhou resupply vehicle. The two bright spots in the image likely correspond to sunlight reflected by the large solar panels on the station and resupply vehicle. In circumstances where communications with satellites have been lost, optical observations can provide useful information about their orbit and status.

Unfortunately, in our current observation campaign, we have not yet detected Tiangong-1. This is common during re-entry as the atmosphere affects the motion of the spacecraft, making it harder to predict.

In addition, at its lower altitude, the station is moving faster with respect to our ground telescope, making it more difficult to observe. In spite of these challenges, we still hope to catch some final images of the space station before re-entry.

The Chinese space station, Tiangong-1 is currently circling as low as 200km above the Earth. Its altitude is decreasing more rapidly each day due to the drag of Earth’s atmosphere and it will eventually come crashing back to Earth. However, the point of re-entry and the location of its final resting place cannot be predicted. This is because the orbit of Tiangong-1 is affected by many complex environmental factors, including the sun’s activity.

Also, the way the station will disintegrate upon reentry cannot be ascertained because its make-up is unknown and is a matter of speculation.

But what is certain is that the 8.5 tonnes Tiangong-1 will not survive its reentry as it heats up and breaks apart. Most of it will be incinerated and will not reach the surface of the Earth. Also it is extremely unlikely that pieces of Tiangong-1 will land on populated areas, let alone cause injuries.

In a similar event, the Soviet Kosmos 954 satellite re-entered the atmosphere in 1978 and crashed in the Northwestern Canadian Territory. The satellite carried a nuclear power source which led to radioactive material being dispersed over the crash zone and required a subsequent clean up. The Canadian claim was eventually settled diplomatically with the USSR paying Canada around $3 million (Canadian).

The fall of the US Skylab resulted in a littering fine issued by the Shire of Esperance in WA.

Tiangong-1 is likely to contain fuel that would have been used to raise its orbit in normal operation. This fuel is highly toxic and should not be handled.

Interestingly, the demise of Tiangong-1 coincides with the reform of the Australian Space Activity Act, which includes among other things the liability of the Australian Government to damages caused by the Space activities of Australian nationals.

The very small likelihood of damage due to the re-entry of space objects such as Tiangong-1 means that the issue of liability focuses on the launch phase of a space mission. The demise of Tiangong-1 and how the subsequent events unfold will, therefore, be of interest from this perspective. Even though a claim was initiated by Canada in the case of Kosmos 954 it never proceeded through the full process of the liability convention. Hopefully this time there will be no damages but then maybe there is a very small probability that the liability convention may be tested.

The first Chinese space lab, Tiangong-1, was home to the crews of the space capsules Shenzhou 9 and Shenzhou 10 in 2012 and 2013 respectively. The first Chinese crewed docking and space walk were part of these missions.

In 2016 and after a few more years in hiberation ground controllers lost contact to Tiangong-1 and no more reboosts took place. It is now nearing its fiery demise as it gradually gets slowed down by the fringes of the Earth's upper atmosphere. 

Very little information has been provided by officials as to why the telemetry link was or had to be cut.

The Inter-Agency Space Debris Coordination Committee (IADC) led by the European Space Agency (ESA) is conducting an international campaign to monitor the approaching re-entry, which is expected between March 30 and April 2nd. 

The exact reentry location of an uncontrolled spacecraft depends on many factors that cannot be precisely modelled. Those factors include sun activity, the irregular surface geometry of the space lab as well as the remaining full mass and slosh effects.

Reentry will happen between 43 deg Northern and Southern latitude including Australia. Night time and clear skies provided we may be in for a nice treat over the Easter holidays. Similar to Skylab in 1975, although only a tenth in size, we may potentially witness the end of Tiangong as a series of fireballs streaking across the sky.

Current Orbit: 203 x 222 km, 42.7 deg inclined to the equator

"China has a legal responsibility (under international law) 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. 

China is a member of UNCOPUOS (United Nations, Committee on Peaceful uses of Outer Space) and a signatory (along with 83 other nations) to the Outer Space Treaty. This means that China has agreed to be legally bound for Space Activities by the following International Treaties;

•    1967 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies 
•    1972 Convention on International Liability for Damage Caused by Space Objects
•    1968 Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space 
•    1975 Convention on Registration of Objects Launched into Outer Space

If Tiangong-1 or any component part of the station does damage toa person, structure or landscape, China can be held responsible for the damage under the 1972 Convention on International Liability for Damage Caused by Space Objects. 
 
As a signatory to the 1972 Liability Convention mentioned above, China is liable to pay compensation for damage which is caused by its space object/components (Tiangong-1) either on the surface of the earth (people and property) or to an aircraft in flight. Any damages caused by the spacecraft in this instance triggers liability. 
 
If the damage is caused elsewhere than on the surface of the earth (i.e. in space) then China will be liable only if fault can be attributed to China for damage, however the treaty does not define what constitutes the fault standard. (In other words there is no legal definition of fault within the context of the Liability Convention.) 
 
Attributing fault for collisions in space has proven difficult. This was the case following the first collision between two satellites in 2009 when the Russian Communications Satellite, ‘Cosmos 2251’ and an active US commercial communications satellite, ‘Iridium 33’. Even though the Liability Convention could have been invoked for that collision, the dispute was settled by the two countries privately, outside the convention. 
 
For example, if Tiangong-1 collides and damages a satellite from Australia or damages people or property within Australia, our government can utilise diplomatic channels to present a claim for damage to China following the procedure outlined under the 1972 Liability Convention."

Tiangong 1 is a rare type of spacecraft – a station capable of supporting human life. There are four other space stations currently in Earth orbit. Genesis 1 and 2 are experimental inflatable space habitats launched by Bigelow Aerospace over a decade ago. No astronaut has ever visited them. Tiangong 2 was launched in 2016 and subsequently a month-long mission to test its systems was carried out by two astronauts. And of course, we have the International Space Station, permanently occupied for the last 17 years.

Tiangong 1 has supported a number of short missions since its launch in 2011. Some were just docking and rendezvous with the Shenzhou supply craft. Two were human spaceflight missions. In 2012 China’s first female astronaut, Liu Yang, travelled to Tiangong 1. After carrying out her assigned medical experiments, she performed a Tai Chi routine designed specifically for space exercise. The second expedition to the station in 2013 included Wang Yaping, the second Chinese woman to go to space. Her mission coincided with the 50th anniversary of the first woman in space, the USSR cosmonaut Valentina Tereshkova in 1963.

The big question is whether any parts of the space station make it down to the surface of the Earth intact. The most common spacecraft parts to survive the heart of re-entry are those with the highest melting temperature. These are titanium pressure vessels – sometimes called space balls – and fuel tanks. Tiangong 1’s fuel tanks are a steel alloy, so they may survive.

At the moment, the re-entry footprint may include southern Australia. We’re old hands at space station re-entry as the US Skylab fell to Earth over Western Australia in 1979. The risks of being hit by falling debris are extremely low so people shouldn’t be concerned about this, especially as Tiangong 1 is tiny compared to Skylab or the ISS.

Not only does the potential for pieces of the Tiangong-1 debris to actually crash to Earth raise questions of where and when, but it also gives rise to issues of potential liability for any damage caused.

The international treaties endorsed through the United Nations that govern space activities incorporate a liability regime. Essentially, damage caused on the Earth’s surface – to people and/or property – may potentially lead to absolute liability for all Launching States associated with the relevant mission. In this case, China would therefore potentially be liable for the full extent of any damage.

That said, the terms of that treaty (known as the 1972 Liability Convention) have only ever been invoked once in the past – in respect of the Soviet Cosmos 954 satellite which crashed into the north-west territories of Canada in 1978. In that case, there was radiation fallout from the crash, which made the situation even more significant. Whilst it is highly unlikely that any serious damage may actually result from the re-entry of Tiangong-1, the potential for liability, and the need for appropriate ‘clean up’ of any debris, will remain a possibility until we know exactly what has happened.

A crashing space station might sound like the Earth is about to feature in a Hollywood disaster movie, but the reality is more modest. China’s Tiangong-1 has a mass of just 8.5 tonnes, certainly not something you would want to have drop on you but far smaller than the International Space Station which is nearly 50 times more massive. The smaller the craft, the less of it is likely to survive re-entry as the friction with the Earth’s atmosphere causes it to burn up. 

China’s secrecy around this nationally significant space mission has meant that the international community doesn’t know what the craft is made of, and that makes estimating the danger more challenging as hardened fuel containers could reach the ground while lightweight panels won’t.

The chances of you being struck by this are essentially zero, as an individual human is a tiny target relative to the Earth which itself is mostly water and even the land is mostly of sparsely populated regions.

We don’t know what happened to the space station in 2016 and China only begrudgingly admitted there was an issue after amateur astronomers had noticed motion that indicated it was out of control.

Simply put the space station no longer responds to commands to fire its engines and ever since that moment was unavoidable and uncontrollably on a collision course with Earth.

It is not a perfect vacuum in low Earth orbit where space stations and satellites reside meaning they are constantly slowing down by running into the wisps of atmosphere that remain hundreds of kilometres above us. The thin atmosphere drags the craft, much as you can feel the air when you put your hand out of a moving car. The spacecraft loses its orbital energy to the thin atmosphere and sinks ever lower, slowly in the beginning and then evermore quickly as it hits ever denser air. Some parts of the upper atmosphere are thick than others meaning the craft slows unpredictably and since it travels around the Earth in just 90 minutes even an uncertainty of a two minutes means the craft could fall anywhere along a 1,000km track.