The Long March 5B rocket, which carried a Chinese space station module, has dropped into low Earth orbit and now risks crashing back down.

The rocket successfully launched the Tianhe module last week, which will become the living quarters of the future Chinese Space Station (CSS). Unfortunately, the 30-metre long rocket also reached orbit, and is now one of the largest ever launches to make an uncontrolled re-entry.

It is uncommon for rockets to reach the velocity necessary to reach orbit, but it is currently travelling around the world once every 90 minutes, or seven kilometres every second. It passes by just north of New York, Madrid, and Beijing, and as far south as Chile and New Zealand.

There are fears that the rocket could land on an inhabited area; the last time a Long March rocket was launched in May 2020, debris was reported falling on villages in the Ivory Coast. The speed of the rocket means scientists still do not yet know when it will fall, but it is likely to do so before 10 May 2021.

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The rocket is likely to come down on 9 May 2021, at approximately 17:23 UTC, with a margin of error of just over a day, the ESA says.

It appears to be dropping at a rate of 16.29 kilometres per day, but it remains difficult to predict where the core state is going to fall.

“This is mainly because atmospheric density, which drives the reduction in orbital altitude to an eventual re-entry, is not well known below 300km in altitude, as spacecraft are seldom active there to gather measurements”, the Agency says.

Adam Smith4 May 2021 14:02

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While it is likely that the rocket will fall into the ocean – simply due to the large percentage of the Earth being covered in water – astronomers believe that some pieces of the rocket will survive re-entry.

This would be the “equivalent of a small plane crash scattered over 100 miles”, according to Jonathan McDowell, Astrophysicist at the Astrophysics Center at Harvard University.

Right now, predicting the rocket’s fall is very difficult, but it is expected that it will return to Earth on 10 May. Once the specific day has been confirmed, experts can apparently narrow its landing time down to a six-hour window.

“The Long March 5B core stage is seven times more massive than the Falcon 9 second stage that caused a lot of press attention a few weeks ago when it re-entered above Seattle and dumped a couple of pressure tanks on Washington state,” McDowell also said. “I think by current standards it’s unacceptable to let it re-enter uncontrolled. Since 1990, nothing over 10 tons has been deliberately left in orbit to re-enter uncontrolled.”

Adam Smith4 May 2021 12:22

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Long March 5B: Tracking the rocket

Currently, the rocket is keeping within those parameters, but has dropped further today. At 10:00am GMT, when the rocket was over Africa, it dropped to nearer 160 kilometres.

Amateur observations from the ground show regular flashes from the rocket in the night sky, suggesting that it is not under any control.

It is likely much of the rocket will break down as it crashes, but some debris will remain.

“It is always difficult to assess the amount of surviving mass and number of fragments without knowing the design of the object, but a reasonable “rule-of-thumb” is about 20-40 per cent of the original dry mass,” Holger Krag, head of the Space Safety Programme Office for the European Space Agency said.

Adam Smith4 May 2021 12:10