Nasa satellite: Estimate of likely impact time narrows

The Upper Atmosphere Research Satellite (UARS) is likely to fall to Earth between 5pm on Friday and 5am on Saturday UK time A dead spacecraft that is tumbling to Earth will re-enter the atmosphere on Friday evening or Saturday morning UK time, according to Nasa’s latest analysis. Most of the bus-sized Upper Atmosphere Research Satellite (UARS) will burn up in the atmosphere, but more than half a tonne of debris is predicted to get through. The falling spacecraft is expected to begin its final descent to Earth sometime between the hours of noon and midnight US Eastern time on Friday (between 5pm Friday and 5am Saturday British Summer Time), according to an update released by the US space agency on Wednesday . The satellite will not be passing over North America at the time of re-entry, but Nasa said it was too early to predict the time and location with more certainty. Further updates will be released by Nasa later on Thursday, and then 12, six and two hours before re-entry. The space agency anticipates that 26 potentially hazardous parts , weighing a total of 532kg, could remain intact and hit the Earth. The debris will spread along an estimated 500-mile corridor of the Earth’s surface. Among the parts expected to survive the fiery re-entry are four titanium fuel tanks, four steel flywheel rims and an aluminium structure that alone weighs 158kg. Depending on their size and shape, the components will strike at speeds of between 55mph (90kph) and 240mph (385kph). Radar stations around the world, including RAF Fylingdales in north Yorkshire, are tracking the object, but there is little chance of predicting with any accuracy where the debris will fall. The spacecraft’s orbit puts a great swathe of the planet in its path between the latitudes of 57 degrees north and south. Mainland Britain lies between 50 and 60 degrees north. The satellite spends more time at higher latitudes, so there is a slightly higher risk in those regions. Most likely by far is that the remains of the satellite will drop into the ocean, or be strewn across one of the planet’s most desolate regions, such as Siberia, the Australian outback or the Canadian tundra. Nasa put the odds of anyone being struck by a falling part of the spacecraft at one in 3,200. The individual risk to a particular person is much less – one in 3,200 multiplied by the billions that live under the satellite’s flight path. There are no confirmed injuries from manmade space debris and no record of significant property damage from a falling satellite. An organisation of major space agencies known as the Inter-Agency Space Debris Coordination Committee (IADC) takes a lead role in monitoring threats from falling space junk and is running back-to-back simulations to work out when, and roughly where, the spacecraft’s remains will impact. If the IADC or the Ministry of Defence, via RAF Fylingdales, found that the UK was at risk, they would inform the Cabinet Office civil contingencies committee, which is responsible for alerting the emergency services. When Nasa’s Skylab fell to Earth in 1979, the space agency put the risk of human injury at 1 in 152, because the odds of the defunct space station striking a city were much higher. The partially controlled Skylab missed its expected impact site in South Africa and crash-landed in Australia. Predicting where the debris will land is difficult for two main reasons. Unpredictable rises in the sun’s activity warm the atmosphere and make it expand, which causes the spacecraft to experience more drag and re-enter more quickly. Another problem comes from uncertainties in the tracking of how the spacecraft disintegrates, which means that even just a few hours before impact, the corridor of the Earth’s surface at risk will be several thousand kilometres long. Under an international treaty, governments are obliged to return any parts of a satellite that are found to the owner, in this case Nasa. The space agency urged anyone who suspected they had found debris from the spacecraft not to touch it and inform the local police. The satellite was launched in 1991 aboard the space shuttle Discovery and decommissioned in 2005. Satellites Space Nasa United States Ian Sample guardian.co.uk

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