ROSAT, a defunct X-ray telescope, is crashing to Earth sooner than expected owing to enhanced solar activity, says Johann-Dietrich Wörner, executive director of DLR, the German lab in charge of the mission. It was thought that the 2.4 tonne spacecraft would deorbit in late October or early November, but Wörner says the re-entry date is now going to be between 20 October and 25 October.
“Increased solar radiation activity has enlarged the atmosphere, increasing the friction on the satellite. So it will come down earlier than expected,” he says. But he can’t say where in that date range the satellite is most likely to deorbit – it depends on fast-fluctuating atmospheric conditions. Heatproof optics mean much more of ROSAT’s mass is expected to survive re-entry compared to the NASA UARS satellite that fell into the Pacific Ocean last month…..
“If the core of ROSAT withstands reentry then a 1.6 tonne piece could hit Earth. But it’s more probable that parts in the mass range of hundreds of kilos will result,” says Wörner. If anyone gets injured by the telescope’s debris – the odds are 3000 to 1 of that happening – three nations will have to pay compensation, DLR points out: the US (which launched it), the UK (where the primary payload was made) and Germany (which ran the mission).
DLR will use data supplied by US Strategic Command and the European Space Agency to track ROSAT’s ever-lowering orbit and give warnings within five hours of impact if populated areas seem at risk.
While many websites, like Heavens Above and N2YO track spacecraft to their bitter end, they often get completely swamped by web users as zero hour approaches and end up unavailable. So for ROSAT’s demise, a team of programmers in Australia is trying a different tack: they have prepared what they hope will be plenty of server capacity for an iPhone-based ROSAT-tracking app called simply ROSAT Reentry.
“Our five servers are each capable of handling more than 600,000 requests per minute. So it’s extremely unlikely that our service will suffer from the same problems as the public spacecraft tracking servers did with UARS,” says Ian Exaudi, who runs the software house behind the app, Creative Intersection of Ashgrove, Queensland. “We’re not out to make serious money on the app. It’s a for-love project more than anything else,” he says.