2. THE PIONEER ANOMALY Previous | Next

On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.

Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.

The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.

People finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.

Nobody knows what causes this anomalous step change in acceleration during fly-bys. However, it appears  fundamentally different to the Pioneer anomaly.

Earlier this year, a major peer-reviewed study from the Jet Propulsion Laboratory examined the data and pronounced the effect real. Which means we can expect to hear a lot more about it.

I suspect those spacecraft are behaving exactly as they should in the areas of space they happen to be in.  It may be that our observations are getting skewed because of variations in space and time where those spacecraft are passing through.  The radio signals from those spacecraft might be undergoing a phase shift because of a time difference instead of a frequency shif caused by motion.  Space and time might be different in front of the Earth than it is behind the Earth in its orbit.  Variations in speed as those spacecraft fly by the Earth might be an illusion whose magnitude depends on the spacecraft position as it flies by.  This is all speculation on my part, but the effect might be observed if an experimenter was looking for it. 

I reported on the American Physical Society meeting in St Louis, Missouri back in April for New Scientist. One of the presentations was by Slava Turyshev, who is leading the official NASA investigation into the Pioneer anomaly. His painstaking studies indicate that nothing more exotic than heat emissions can account for at least part of the drift. Turns out that Pioneer 11 gives off heat in some directions more than others

which would push it off course. It only accounts for around a third of the drift, but it’s a start. They’re still looking at things like the spacecraft’s optical properties, and the heat drift might turn out to be enough to account for all of it. Anyway, my report on it is here

http://space.newscientist.com/article/dn13676-pioneer-spacecraft      

There's a prototype of Pioneer in the Smithsonian National Air and Space Museum in Washington. I wondered if we might find out more about the craft's thermal properties by running a series of tests on it. But Turyshev reckons it would be too expensive to do and they simply don't have enough manpower. Also it's not clear that the protptype has exactly the same surface coating, so any results could be a red herring.