Give or take 16 hours, the 23-tonne rocket booster of a Long March 5B rocket will re-enter Earth’s atmosphere at 12:24am GMT on Sunday morning.
The core stage of China’s recent launch of its Wentian module to the Tiangong Space Station could, theoretically, land anywhere between 42 degrees north and south of the equator.
US-based Aerospace Corporation tracks rocket and payload in orbit and says that the rocket body – of which roughly four to nine tonnes is expected to survive re-entry and reach the surface – is currently predicted to land somewhere in the middle east.
That prediction will be refined as the rocket body gets closer to re-entry, although Aerospace Corp notes that a re-entry location could occur anywhere along the blue or yellow ground tracks indicated on its prediction map.
This is the third uncontrolled Long March 5B core re-entry
Long March 5B rockets have a history of making the world nervous.
That’s because the core stages are hefty pieces of spacecraft making uncontrolled returns to Earth.
In 2021, the core stage of the 5B-Y2 rocket plummeted into the Indian Ocean over the Maldives (as witnessed by members of the Australian Cricket Team).
Prior to that, parts of the first 5B-Y1 rocket landed on villages in Cote d’Ivoire.
Including the upcoming re-entry of 5B-Y3’s core, these re-entries represent the three biggest objects to have uncontrolled returns to earth since the Columbia space shuttle (74 tonnes) re-entry tragedy in 2003.
Prior to this, the only other objects over 20 tonnes were Mir (2001, 130 tonnes) and Skylab (1979, 77 tonnes) – which landed over Esperance in Western Australia.
That means as many uncontrolled objects over 20 tonnes have returned to Earth in the last three years as the preceding six decades of space travel.
And although the risk of being personally hit by a piece of space debris in less than one-in-a-trillion (and non-existent if you’re not in the re-entry trajectory), recent research suggests there’s a 10% chance someone on Earth will be killed by debris in the next decade, and that risk is disproportionately borne by those in the Global South.
Predicting the final resting place of an uncontrolled rocket is fraught with uncertainty – atmospheric drag, angle and rotational variation of object re-entry – so tracking services will try to account for those and caveat their predictions.
Dr Darren McKnight from satellite tracking company LeoLabs points out that the easier thing would be to avoid the situation by having controlled re-entries.
“There are many, many things we have gotten much better on in the space age, about being to calculate and to determine,” he says.
“But re-entry is not one of them.
“It’s important for people to understand that among the 10 tough things that we do in space, debris re-entry is probably one of the toughest ones to predict.
“We should take more responsibility about not letting us get in a situation like this.”
Tracking the final flight
Objects orbit the earth at tremendous speed – taking just an hour to orbit over half the planet – so an estimate off by just 60 seconds can result in debris appearing in a very different location to its original prediction.
For context, a one-minute miscalculation for an object hurtling through space at seven kilometres per second means it could land anywhere across a 420km flight path.
That’s roughly the distance between Canberra and Melbourne.
In reality, a re-entry occurring within a minute of its final prediction would be incredibly precise.
Estimates made at the beginning of an object’s final orbit could still result in a crash-landing anywhere along a 7,000km re-entry path.
You can follow Aerospace Corp’s estimates here.
Matthew Agius is a science writer for Cosmos Magazine.
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