Why we can’t predict where Chinese station will fall?


The current estimated reentry time for the abandoned Chinese space station Tiangong-1 is anytime from morning of 31 March to the afternoon of 1 April UTC. Even less we can guess about the exact place of fall. The only available expectation is that it will fall anywhere between 43ºN and 43ºS. Why the fall can’t be pointed with more adequate precision? And does the fall pose a threat to US and Wisconsin?

It is somewhat strange, that in the era of precise telemetry and computer models scientists and engineers can’t tell the place with some reasonable degree of probability. Current coordinates of the Tiangong-1 are well known and tracked by multiple space agencies, for example by the NASA, European ESA’s Space Debris Office, by the Russians and of course by the China itself. The reason for such uncertainty in pointing exact coordinates is easily understandable if we take into account the catastrophic nature of the event.

Tiangong-1, China’s first prototype space station is relatively large object. It’s weight is 18,753 lb, dimensions is 34.1’x11.0′. It is cylinder-shaped and has big solar panels attached. It has known and predictable trajectory while on orbit. When it will reenter the Earth atmosphere, however, it’s path will become unstable and erratic. Will it break down or will it fall in one piece? These factors are unknown.

Wisconsin fits in the 43ºN and 43ºS area, as fits the entire mainland US. However it should be noted that the probability to really harm some inhabited territories are extremely low. Scientists believe that it only one chance it trillion that at least some debris will reach the ground and affect the life in some city or town.

Tiangong-1 is not the first and definitely not the largest space station that will end up burning in the planet’s atmosphere. The biggest one was Soviet ‘Mir’ station which fell back to the Earth in 2001. It’s mass was 285,940. It fell to the Pacific ocean on 23 March 2001.

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