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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."
Pioneer 10 and 11, of course (not 11 and 12)
The Pioneer 10 & 11 spacecraft both flew by Jupiter, and Pioneer 11 went on to Saturn encounter.
I remember it well - while a grad student at the Lunar & Plantetary Labs, I helped with the Imaging Photopolarimeter during Saturn Encounter.
The spacecraft, designed in the early 1970's, had essentially no onboard memory, so instructions had to be uploaded in real time. The several hour-long communications delay made for real excitement at encounter (Did the spacecraft survive the ring crossing? Did the instruction arrive? Did the sensor point in the correct direction? Is it returning images?)
We'd spent months in advance, preparing alternative sequences for the encounter. Each sequence was on punched papertape. Then, at encounter in September 1979, we'd pick the tape, mount it on a teletype, and send the data out over the NASA deep space network, then anxiously wait to see if the instructions worked on Pioneer 11.
Wait, 60 isn't divisible with 10 now?
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.
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