The Tiangong-1 Chinese Space Station went up to space in 2011 and it lost control in 2016 and has been on the descent course ever since. It is expected to crash back into the planet between March 30 and April 6. The experts do not know where it will hit but all they have been able to narrow down is somewhere between the latitudes 43 degrees north and 43 degrees south.
This includes a number of highly populated cities including New York, Barcelona, Beijing, Chicago, Istanbul, Rome and Toronto. The 8.5-tonne craft Tiangong-1 space station can hit anywhere along this line and it is impossible to predict where before re-entry.
Explaining why it could hit these cities Dr. Hugh Lewis, senior lecturer in Aerospace Engineering at the University of Southampton compared the geometrical processes at work to crossing the road. Speaking to MailOnline, he said:
“The spacecraft is travelling around a more or less circular orbit, which is tipped with respect to the equator at 43°. If you plot this path on a map of the Earth, it produces a sine wave pattern, with the slower curve of the wave in northern and southern latitudes and the faster straighter sections running from east to west. If you imagine the green low-risk area on the map is the part of the road we’re trying to walk across, the quickest way is to go at 90 degrees – straight across. When the spacecraft crosses the equator, it’s crossing the road at this point, and it does so really fast. When it goes across the red bands further north and south, it’s crossing at a steeper angle – almost parallel to the road. It takes longer to cross at these latitudes, which is why it has a higher risk of coming down here.”
Experts from the European Space Agency (ESA), based in Paris, are among those tracking Tiangong-1. The Space Debris Office in Darmstadt, Germany just predicted that it will re-enter sometime between March 30 and April 6. But even they don’t know where it will hit.
Speaking to MailOnline, Dr Lewis added: “We can’t say precisely where, as we don’t know which orbit it will come in on. At this point in time, it’s very difficult to say. If you take how far in advance you make your prediction, the rule of thumb for error is around 10 percent. At the moment, that’s roughly 10 days or 160 possible orbits. If we were to predict again with a week to go, this would narrow to less than one day or 16 possible orbits. My expectation is that what little of the craft survives the atmosphere will impact the ocean.”
Most of the space station will burn up upon re-entry but around 10 to 40 % is expected to survive as debris and could impact the Earth. The spacecraft has sped up in the recent months. It was falling at 1.5 km per week in October whereas it is now falling by more than 6km per week now.
“Every couple of years something like this happens, but Tiangong-1 is big and dense so we need to keep an eye on it”, Jonathan McDowell, an astrophysicist from Harvard University told the Guardian. “It is only in the final week or so that we are going to be able to start speaking about it with more confidence. I would guess that a few pieces will survive re-entry. But we will only know where they are going to land after after the fact.”
Aerospace Corp has also issued its own forecast over the likelihood of being hit by falling debris. In a written statement, a company spokesman said: “When considering the worst-case locations, the probability that a specific person will be struck by Tiangong-1 debris is about one million times smaller than the odds of winning the Powerball jackpot. In the history of spaceflight, no known person has ever been harmed by reentering space debris. Only one person has ever been recorded as being hit by a piece of space debris and, fortunately, she was not injured.”
Holger Krag, head of ESA’s Space Debris Office, said: “Owing to the geometry of the station’s orbit, we can already exclude the possibility that any fragments will fall over any spot further north than 43°N or further south than 43°S. This means that re-entry may take place over any spot on Earth between these latitudes, which includes several European countries, for example. The date, time and geographic footprint of the re-entry can only be predicted with large uncertainties. Even shortly before re-entry, only a very large time and geographical window can be estimated.”
We have waited so long for the Tiangong-1 to fall. I am sure we can wait a week more to see where it actually ends up.