Original URL: http://www.theregister.co.uk/2009/11/13/speeding_satellite/

Quickening satellite quickens pulses at ESA

Speeding Rosetta orbiter baffles astro-boffins

By Pratik Desai

Posted in Science, 13th November 2009 15:32 GMT

Baffled Boffins at the European Space Agency (ESA) are hoping that today's Earth fly-by of the Rosetta satellite will shed light on a problem of significant gravity.

At 07:45GMT this morning, the ESA's Rosetta started its third fly-past of the Earth, looking for a gravitational sling-shot. This particular event is being closely watched by scientists on both sides of the Atlantic, as since 1990 a problem has been bothering eggheads at both NASA and ESA.

Their satellites appear sometimes to be speeding up beyond the predictions set out by the laws of Physics. Even more confusingly, the speed anomaly appears to be random, with many similar missions not experiencing it at all.

Previous NASA missions, including Pioneers 10 and 11, have been subject to the effect. Rosetta experienced the anomaly itself on its first fly-by in 2005, when it was found to have accelerated to 0.0018 m/s above what was expected. However, the satellite did not display such an effect on its second visit to us in 2007.

One could wonder as to whether such a minuscule change in the satellite's speed is worth getting worried about. But a paper released by ESA scientists describes how the satellite had to be manoeuvred in order to compensate for the worrying burst of speed, which could have led to serious consequences if left unchecked.

It is the inability to predict the anomaly that has got scientists into a tizzy, and the lack of a simple answer has led to numerous exotic ideas having been put forward. These include potential distortions to Earth's space-time fabric, the influence of dark matter and even the prospect of changes being required to the General theory of relativity.

These are obviously the sorts of things that slide-rule toting geeks dream of, and the space-botherers are suitably aflutter at the possibilities. In the words of ESA's lead flight dynamics specialist, Trevor Morley: "As it stands now, no one knows what's behind this - it really is a mystery. And your prediction as to whether Rosetta will experience any swing by speed anomaly at all on 13 November is as good as anyone's."

So the boffins are excited. They're not sure if there is anything to be excited about, but they are excited. ®