Rosetta Fly-By To Probe "Pioneer Anomaly"

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."

Comments

Just so nobody fucks up the units from the start

[Anonymous Coward]

45000km/hr 45 000 km = 45 000 000 meters = 45 000 000 000 millimeters. 1 hour = 60 minutes = 3600 seconds. Rosetta's velocity is thus 12 500 000 millimeters per second.

Not the Pioneer Anomaly

[CheshireCatCO]

This isn't the Pioneer anomaly. The latter was seen not in flybys but during extended cruise phases with no maneuvers. As far as I know, it has only been seen in Pioneers, although that may be due to the particular nature of those spacecraft that make them excellent tests for this effect. (Assuming it's not entirely intrinsic to the spacecraft in the first place.)

This effect is a flyby effect and is different from the Pioneer Anomaly, as the article itself pretty clearly notes.

Re:Not the Pioneer Anomaly

[BadEvilYoda]

The Planetary Society has an interesting FAQ on this subject: http://www.planetary.org/programs/projects/innovative_technologies/pioneer_anomaly/update_20050720.html

Also explains why it is seen with Pioneer 10 and 11 and not Voyager 1 or 2 or other more "modern" spacecraft.

From the FAQ: The Pioneers are spin-stabilized spacecraft. The Voyagers are three-axis stabilized craft that fire thrusters to maintain their orientation in space or to slew around and point their instruments. Those thruster firings would introduce uncertainties in the tracking data that would overwhelm any effect as small as that occurring with Pioneer. This difference in the way the spacecraft are stabilized actually is one of the reasons the Pioneer data are so important and unique. Most current spacecraft are three-axis stabilized, not spin stabilized.

Re:Cliff Stoll?

[Cliff Stoll]

Yep, same guy.

Before Cuckoo's Egg, I was better known as a planetary scientist. My PhD dissertation relied on polarization data taken by Pioneer 10 & 11 to understand the scattering characteristics of Jupiter's upper atmosphere.

Cheers,
-Cliff