An out of control Russian spacecraft could crash land on southern England sometime this weekend, scientists have warned.
The minibus-sized Phobos Grunt is loaded with 11 tonnes of fuel that was supposed to take it to Mars and one of its moons.
But the on-board computer failed shortly after take-off last November and the spacecraft's orbit of the Earth has been getting lower ever since.
Chief engineer at the UK Space Agency Professor Richard Crowther said it is expected to explode as it enters the atmosphere, scattering debris along a 200km track - anywhere between the M4 corridor and the Falkland Islands.
But he told Sky News that fragments are most likely to fall into the sea: "If you look at the Earth from space, most of it is covered by water.
"The UK is very small by comparison. The probability of it falling in such a small area is very, very low.
"It doesn't keep me awake at night."
The Russian space agency Roscosmos estimates that between 20 and 30 fragments, weighing 200kg in total, will make it back to the Earth's surface.
RAF Fylingdales in Yorkshire, which normally scans the skies for nuclear missiles, will track the craft's re-entry.
But scientists say it's impossible to predict exactly where and when Phobos Grunt will plummet through the atmosphere. Even on its last 90-minute orbit of the Earth they will only be able to predict where the debris will land to within 4,300km.
Prof Crowther said one object a day falls from orbit. Most are small - such as spanners dropped by astronauts - and burn up completely on re-entry.
But he warned that space agencies must in future design satellites to disintegrate when they plummet to Earth.
"Rather than making them as robust as possible, so they survive the hazardous environment of space, we should design them to break up and burn up on entry so as little as possible makes it down to Earth," he said.