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

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:Not the Pioneer Anomaly

[DynaSoar]

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

The situations in which they are measured differ. This is what TFA states. But it is by no means certain that the cause differs, and TFA makes no claims one way or the other. John Anderson of JPL and colleagues published in 1998 and 2002 examinations of the Pioneers, Ulysses and Galileo trajectories and hypothesized a single phenomenon, a time dilation effect due to gravity. The fly by effects may be more pronounced due to greater frame dragging than trajectories more or less straight to the heliopause, but the velocity changes when noted are of the same magnitude. Mbelek's recent paper looks at fly by data to determine whether special relativity may account for the anomalies in fly bys, but does not exclude applying the same to non-fly by situations. If the math proves valid, and sufficient data is obtained, then it may be able to be determined whether the two discrepencies have a single cause. The data collection on Rosetta is being done in part to try to determine whether or not they are the same. If there weren't at least hypothesized 'same or different' consideration, there'd be no mention of Pioneers.

Re:Not the Pioneer Anomaly

[DynaSoar]

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.

According to Wikipedia the problem is that other spacecrafts have too much built-in disturbance (e.g. from thrusters) to measure such a small effect.

However I wonder why no one has built a spacecraft that explicitly avoids all such disturbances so the effect can be checked with the best accuracy possible. Also, put all sorts of additional measurement devices on it (of course only of the sort that doesn't disturb the path measurement, e.g. nothing producing large amounts of heat), e.g. to look at the matter density around (maybe there's simply more gas out there than expected, which is slowing down the space craft by friction). And of course, also measure as much of the internal state as possible, in order to find out about unexpected effects like gas leaks.

The problem with Voyager data is that they course correct using thrusters and so their exact location is more uncertain. Pioneers and most system bound probes are spin stabilized and so can be measured and predicted more reliably.

Several probes have been testing some of the relevant effects in Earth orbit for years. LAGEOS I and II detected an effect of relativity called frame dragging. This is an effect which is hypothisized to be greater near a planet, but also noticeable across great solar system distances. Gravity Probe B has measured it to a greater degree, is still collecting data, and is observing some unusual effects within the data. One of the LAGEOS teams is planning another probe, LARES, to be launched within a year or so, looking at this effect (also called the Lense-Thirring effect) with greater accuracy. Getting good numbers on this effect will allow others to determine if the effect is involved in any of the cases noted. It may also help to explain why it is not seen in different instances on the same probe (Rosetta 2005 vs. 2007) if the frame dragging is due to rotation, is asymmetrical, and the probes are found to have passed through the planetary field with vs, opposite the direction of rotation.

That's Pioneer 10 and 11

[Cliff Stoll]

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.

Re:First post !

[maxwell demon]

I'm sorry but your post encountered a fly-by anomaly when passing one of the big Internet routers, and therefore was delayed, thus allowing other posts to come before it.

Re:Metric only

[Zerak-Tul]

Wait, 60 isn't divisible with 10 now?

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

Re:Metric only

[theIsovist]

Apparently so is math