Debris from a Chinese rocket is expected to fall back to Earth in an uncontrolled re-entry this weekend.
The main segment from the Long March-5b vehicle was used to launch the first module of China’s new space station last month.
At 18 tonnes it is one of the largest items in decades to have an undirected dive into the atmosphere.
The US on Thursday said it was watching the path of the object but currently had no plans to shoot it down.
“We’re hopeful that it will land in a place where it won’t harm anyone,” US Defense Secretary Lloyd Austin said. “Hopefully in the ocean, or someplace like that.”
Various space debris modelling experts are pointing to late Saturday or early Sunday (GMT) as the likely moment of re-entry. However, such projections are always highly uncertain.
Originally injected into an elliptical orbit approximately 160km by 375km above Earth’s surface on 29 April, the Long March-5b core stage has been losing height ever since.
Just how quickly the core’s orbit will continue to decay will depend on the density of air it encounters at altitude and the amount of drag this produces. These details are poorly known.
The European Space Agency has confirmed China’s Long March 5B rocket – which was launched into the skies with much fanfare a mere week ago – has dropped into low Earth orbit.
US space research organisation the Aerospace Corporation has forecast the 18 tonne piece of ejected rocket will re-enter the Earth’s atmosphere at around 4am on Sunday, May 9, Greenwich Mean Time, which would be 2pm AEST.
The current trajectory puts the space junk just east of Australia and close to New Zealand’s North Island as it renters.
However, those projections are highly uncertain and even when it renters its likely to travel some distance before hitting land or sea. Much, but by no means all, of the rocket is likely to burn up before it reaches the surface.
It could make contact with the Earth’s surface anywhere between the latitudes of 41.5 degrees north or south, a wide band that includes much of Asia, Africa, the Americas and Australia as well as the central portions of the Atlantic and Pacific oceans south of New York, Madrid and Beijing and north of Tasmania and Buenos Aires.
