Rosetta Fly-By To Probe "Pioneer Anomaly" 89
DynaSoar writes "On Friday November 13th, ESA'a Rosetta probe will get its third and final gravity assist slingshot from Earth on its way to its primary targets, the asteroid Lutetia and Comet 67P/Churyumov-Gerasimenko. But the slingshot itself will allow ESA scientists to examine the trajectory for unusual changes seen in several other probes' velocities. An unaccountable variation was first noticed as excess speed in Pioneers 11 and 12, and has since been called the Pioneer Anomaly. More troubling than mere speed increase is the inconsistency of the effect. While Galileo and NEAR had appreciable speed increases, Cassini and Messenger did not. Rosetta itself gained more speed than expected from its 2005 fly-by, but only the expected amount from its 2007 fly-by. Several theories have been advanced, from mundane atmospheric drag to exotic variations on special relativity, but none are so far adequate to explain both the unexpected velocity increases and the lack of them in different instances. Armed with tracking hardware and software capable of measuring Rosetta's velocity within a few millimeters per second while it flies past at 45,000 km/hr, ESA will be gathering data which it hopes will help unravel the mystery."
Re:Is it Dust? (Score:2, Insightful)
That might explain the Pioneer slowdown, but I don't think it could explain the energy gain on fly-by.
Re:Just so nobody fucks up the units from the star (Score:3, Insightful)
I think you mean 3.74698572 × 10^12 Planck Lengths per Planck Time. It's high time we abandonded this archaic 'metric' system for one that more accurately expresses the universe.
Re:Not the Pioneer Anomaly (Score:3, Insightful)
If there weren't at least hypothesized 'same or different' consideration, there'd be no mention of Pioneers.
Unless they're often confused, which they are. Two anomalies involve spacecraft trajectories are obviously easy to mix up, whether or not there is any reason to suspect a relationship.
Re:Not the Pioneer Anomaly (Score:2, Insightful)
...This effect is a flyby effect and is different from the Pioneer Anomaly...
How does anyone know? Everybody assumes (believes) that the spacecraft as a whole are scrupulously electrically neutral. If that is not the case, which is very likely, then the electrical and magnetic fields in space would certainly affect its motion. An electric field, even a very weak one, affects a charged object 36 orders of magnitude more than gravity. Depending on the polarity of the charge, which can sometimes be negative and sometimes positive, there can be a change of either slowing down or speeding up.
The particles of the solar wind (electrons) ACCELERATE by the action of an electric field, where as they should slow down slightly if gravity were the only force affecting them. The Pioneer probes may have a slight positive charge, which means they would slow down a little more than we would expect by gravity alone.