Orbital mechanics to be revised again?

The March 8 issue of the Economist has an interesting article about how spacecraft apparently are not following their expected trajectories:

In 1990 mission controllers at the Jet Propulsion Laboratory (JPL) in Pasadena, California . . . noticed something odd happen to a Jupiter-bound craft, called Galileo. As it was flung around the Earth in what is known as a slingshot manoeuvre . . . , Galileo picked up more velocity than expected. Not much. Four millimetres a second, to be precise. But well within the range that can reliably be detected. . .

Once might be happenstance. But this strange extra acceleration was seen subsequently with two other craft. . . So a team from JPL has got together to analyse all of the slingshot manoeuvres that have been carried out over the years, to see if they really do involve a small but systematic extra boost. The answer is that they do.

Altogether, John Anderson and his colleagues analysed six slingshots involving five different spacecraft. Their paper on the matter is about to be published in Physical Review Letters. Crucially for the idea that there really is a systematic flaw in the laws of physics as they are understood today, their data can be described by a simple formula. It is therefore possible to predict what should happen on future occasions.

Anderson and his colleagues plan to test their theory when they receive data from Rosetta, which executed a slingshot maneuver in November. I hope I hear about the results.

If I had any readers, I’d ask the physicists if they knew anything about this.

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