A reentry the Chinese rocket CZ-5B had a 1,86% chance of occurring over Brazil according to a calculation made by BRAMON from the last re-entry forecast released on Wednesday (5). According to the calculations of Joseph Remis, the rocket was due to re-enter at about 02h17 this Sunday (9).

But as the forecast is made much in advance, it had a margin of error of about 21 hours and, within that margin, the object would make 9 passes over the Brazil.

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New calculations released on the morning of Thursday (6) indicate that the re-entry should occur a little earlier, at 0:06 on Sunday (9), but with a margin of error of 21 hours, which adds an extra passage on the southern Brazil and raises the possibility of reentry over the country to 1,92%.

It is worth emphasizing that, during the re-entry process, a large part of the rocket must be consumed by the atmosphereleaving only a few more resistant and smaller parts, such as fuel tanks, which fall at a very reduced speed. The chance that they will fall into an inhabited area and may cause some type of damage to the ground is very small, although it cannot be neglected.

Meet the Chinese rocket CZ-5B

O first stage Long March 5B was used to put the first module of the chinese space station Tiangong, last week. 

After fulfilling its mission, the piece was discarded in an elliptical orbit around our planet, which places it at 375 km of altitude at the most distant point and 170 km at the nearest point.

But the friction with the atmosphere at the lowest point of this trajectory causes it to lose energy and get closer and closer, until the moment when it will perform an uncontrolled reentry.

Launch of Long March 5B with the first module of the Chinese space station. The first stage is where the auxiliary thrusters are.
Launch of Long March 5B with the first module of the Chinese space station. The first stage is where the auxiliary thrusters are. Image: CNSA

Small objects reentering the atmosphere are usually incinerated by the heat generated by the friction, but the first stage of Long March 5B cannot be considered “small”: it is 33 meters long and 5 meters in diameter, weighing 21 tons. This means that a considerable part can reach "somewhere" on Earth.

According to the website SpaceNews, this will be one of the largest uncontrolled reentry of a spacecraft, and the wreckage has the potential to reach an inhabited area.

The 41,5 degree orbital inclination means that the first stage passes a little further north in New York, Madrid and Beijing, and further south in the southern region of Chile and Wellington, in the New Zealand.

Reentry can take place anywhere in this area, which also includes Brazil. Considering that 70% of the surface of our planet is covered by oceans, it is likely that the first stage of Long March 5B will reach one of them.

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But the possibility that it will reach dry land, or an inhabited region, still exists: in 1979, a miscalculation caused pieces of the first spacial station American company, Skylab, would reach Western Australia.

In early March, part of the French rocket Ariane 44L, which took off in 1992, reentered our atmosphere over northern Brazil, generating a fireball that was seen in the skies of Ceará and Pará, more specifically in the capital region, Belém. There is no record of pieces reaching the ground. 

China intends to complete the construction of the Tiangong space station by 2022. For that purpose, 10 more missions will be necessary: ​​two for the launch of additional modules, four manned missions and four cargo missions. 

* Marcelo Zurita with Rafael Rigues

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