A new post on NASA’s official Twitter account  said of the falling satellite: “Re-entry prediction now later than expected – tonight or late Saturday morning,” at just before noon Eastern Time.

It seemed that NASA’s earlier prediction of a landing late this afternoon was wrong. A second update from NASA said, “predicted re-entry moving later.”

Meanwhile, NASA official website reveals that the satellite‘s orientation has changed during its plunge – and that its rate of descent was “changing”, making it difficult for NASA computers to predict the time or place of landing.

“There is now a low probability debris that survives re-entry will land in the United States.”

The falling satellite is one of the thousands of objects in Earth orbit being tracked by NASA

The space agency says there is a one in 3,200 chance the falling satellite will hit someone.

The satellite, which has six tons, is being tracked by all available equipment including a giant radar at RAF Fylingdales on the North York Moors on its path towards Earth.

NASA admits that it cannot predict the time or place of re-entry with any certainty – “but predictions will become more refined in the next 12 to 18 hours.”

A period of “12 to 18 hours” seems unnervingly close to when the huge Upper Atmosphere Research Satellite (UARS) will break up on entering the Earth’s atmosphere, throwing chunks of metal weighing up to 350 lb across hundreds of miles.

The space agency said it will only know 2 hours before impact where it will land and even that prediction will only be accurate to the nearest 6,000 miles.

The satellite landing could be anywhere between the 57th parallel north, which crosses Britain at around Inverness, and the 57th parallel south, which passes just below South America.

Worldwide interest in the satellite is growing: a website set up to “track” the falling satellite is constantly crashing under incredible demand, and an app for Android smartphones, Satellite AR, allows people to “see” where it is at any moment.

An amazing video captured the satellite earlier this week as NASA experts slowly narrowed down the area where it could strike.

Astrophotographer Thierry Legault’s clip, shot in northern France, shows the 20-year-old UARS satellite, appearing as a beaming mass of light as it careers to Earth.

The station at RAF Fylingdalers was originally built at the height of the Cold War to track any incoming ballistic missile attack – a role it still performs.

A RAF spokeswoman said:

“The Space Operations Room at Royal Air Force Fylingdales is manned 24 hours a day by specialist Royal Air Force and civilian personnel, and its operators will be working to track the UARS object as it returns to the atmosphere.

“The Solid State Phased Array Radar is being tasked by the United States Air Force and the Royal Air Force to concentrate its radar energy towards the object in order to track its final orbit.”

“This information will then be used by various different agencies to predict the path of re-entry into the Earth’s atmosphere.”

Initially, the satellite was expected to come crashing down through the atmosphere on Friday evening, GMT. On Thursday, the Aerospace Corporation in California predicted that re-entry will occur over the Pacific Ocean.

The satellite, which is 20-year-old, is the biggest NASA spacecraft to fall uncontrolled from the sky in 32 years.

The satellite is expected to break into more than 100 pieces as it enters the atmosphere, most of it burning up.

The heaviest metal parts are expected to reach Earth, the biggest chunk weighing about 300 lb (135 kg). The debris could be scattered over an area about 500 miles long.

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