On 29 April, China launched the first module of its biggest space station yet atop a Long March 5B rocket. Now, part of that rocket is hurtling back towards Earth, and there is no way to predict exactly where or when it will land.
Most large rockets perform a controlled re-entry when they return from their missions in space, with operators often taking care to smash them down in the ocean and avoid any potentially inhabited areas. However, the China National Space Administration has a history of allowing its spacecraft to perform uncontrolled re-entries, sometimes even smashing down into populated towns.
Long March 5B is specially designed to launch heavy space station parts, so it is particularly large. It consists of four boosters surrounding a core that is 30 metres long and weighs about 20 tonnes. The boosters detached shortly after the launch as expected. The core is now tumbling wildly as it orbits at speeds exceeding 7.5 kilometres per second.
At that speed, it circles the planet about once every 90 minutes, which makes predicting where it will land extraordinarily difficult. Even a tiny change in when it hits Earth’s atmosphere could drastically affect where the rocket smashes down – based on the booster’s current orbit, it could end up landing as far north as New York or Madrid, or as far south as Tasmania.
Some parts of the rocket will almost certainly burn up as it travels through the atmosphere, but it’s so large that it will not disintegrate completely. The previous launch of a Long March 5B rocket also had an uncontrolled re-entry, which was the fourth largest such crash ever.
Most of the debris splashed down in the Atlantic Ocean, but if it had entered the atmosphere less than an hour earlier it could have landed somewhere in the densely populated eastern US.
The most likely outcome for this rocket core is for it to land somewhere in water as well, because oceans cover the majority of the planet, but we won’t know for sure until it lands. That is expected to happen between 5 May and 8 May.
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