@soccerdadforlife - 

Hi, soccerdad... yes, all that is pretty standard stuff... i.e. "radar techniques". The interesting thing is that they don't know what is causing it and haven't been able to figure it out over a decade. As to a leak, I find it a little difficult to believe that all of these affected spacecraft ALL had a leak each and every time. The thought here, although conjecture, is that these folks aren't seeing the answer because their paradigm may not allow them to see it. This is much like how evolutionism is slowing becoming unraveled but its proponents cannot find it themselves to abandon it. If there is a change in the speed of light or an unexpected phenomenon due to gravity, their own "beliefs" may cause them to overlook critical evidence for a discovery of the real cause. Blessings, Mr.Vee

@soccerdadforlife - 

Hmmm... I don't know about the dust.
Wikipedia has some info that might be important here...

"Analysis of the radio tracking data from the Pioneer 10 and 11 spacecraft at distances between 20–70 AU from the Sun has consistently indicated the presence of a small but anomalous Doppler frequency drift. The drift can be interpreted as due to a constant acceleration of (8.74 ± 1.33) × 10−10 m/s2 directed towards the Sun. Although it is suspected that there is a systematic origin to the effect, none has been found. As a result, there is growing interest in the nature of this anomaly."

This means that there is a "constant pull" toward the sun at 20-70 AU from the sun. The Kuiper Belt is at 30-55 AU. So there is a correlation there but the direction of deacceleration of Pioneer 10 &11 heading out of the solar system seems to suggest a gravitional anomaly toward the sun and not to nearby bodies. Now there two data transmissions that were successful after passing through the Kuiper Belt. Again from Wikipedia...

March 2, 2002 - Successful reception of telemetry. 39 minutes of clean data received from a distance of 79.83 AU.
April 27, 2002 - The last successful reception of telemetry. 33 minutes of clean data received from a distance of 80.22 AU.

If it were "dust", this would mean that the first 10 and last 15 AU would have not shown the effect. While we might have suspected "dust" as the culprit in the Kuiper Belt, it wouldn't seem plausible before and after it. Yet the report is that the anomaly was observed from all the way from 20AU to 70 AU. Also, the same Wikipedia article gives an instrumentation list aboard the Pioneer 10 (and 11) which would have been instrumental in detecting such things. So it sounds to me like misunderstanding light speed and/or gravity theory may be now "on deck" as the issues.

As you might remember, I mentioned some time back that visual effects over large spans of space might be affected by interstellar dust and gas affecting the permittivity of space giving us incorrect impressions of how far stellar objects are away from the earth. My real point here is ... it appears that when we consider physical phenomena at much larger distances than we've been able to deal with adequately and consistently, there seems to be enough doubt that we truly understand effects that may be present at those distances. It brings strong question to the universal assumption that certain effects are truly uniform over vast distances in a media like a vacuum or even in a heterogeneous medium like interstellar space. Perhaps this is only conjecture but it does seem like there is room for questioning the common assumptions regarding all these things at interstellar distances even though "effects at close promimity" could be fairly well known. Mr.Vee

@soccerdadforlife - 

re: dust as friction
I wouldn't disagree with that at all except the condition was observed from 20 to 70 AU from the sun. The Kuiper Belt is at 30 to 55 AU from the sun and contains all sorts of small planetlets (like Pluto and Charon) and certainly dust. The de-acceleration condition was described as "constant". So...

1. dust is not plentiful at 20 - 30 AU
2. dust is plentiful at 30 - 55 AU
3. dust is not plentiful at 55 - 70 AU

means that dust density varies therefore the force applied by "dust" varies. The condition was described as "constant"
so logically it cannot be the "dust" causing it. Now if the observation is incorrect and the condition is not constant, we would have another thing altogether and I'd certainly consider "dust" as a potential culprit.

Now you do have an interesting point with regard to ice crystals and heavy metal ions and the shielding effect to higher energy radiation and letting the visible light spectrum pass along with UV and IR. Very interesting observation! Mr.Vee

@soccerdadforlife - 

re: shielding
Good point. However, it does offer a potential explanation for intervening disruptions in "observed phenomenon" to cause errors in estimations of matters dealing with celestial physics. A good deal of stellar UV makes it to earth so its enough to observe although I haven't considered if there would be a noticeable difference around the ecliptic.

re: dust
By definition, why would we call the Kuiper Belt what it is? Because of the presence of small planetary bodies, asteroids, space rocks, ice, and presumably dust as well. Since Pioneer 10 & 11 had instrumentation present on board
that could measure such things and was still transmitting data during its transit through the Kuiper Belt and it is presumed that the scientists associated with the missions would have asked the same question and have discounted it already seems to speak for the fact that dust wasn't an issue here.

Here's an excerpt from the Wikipedia article for Pioneer 11...

"Instruments on the Pioneer 11 probe studied the interplanetary and planetary magnetic fields; solar wind properties; cosmic rays; the transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; the atmospheres of planets and satellites; and higher layers of the atmospheres of Jupiter and Saturn, and the surfaces of some of their satellites. The instruments carried for these experiments were a magnetometer, a plasma analyzer (for solar wind), a charged-particle detector, an ion detector, non-imaging telescopes with overlapping fields of view to detect sunlight reflected from passing meteoroids, sealed pressurized cells of argon and nitrogen gas for measuring penetration of meteoroids, an ultraviolet photometer, an infrared radiometer, and an imaging photopolarimeter, which produced photographs and measured their polarization. Further scientific information was obtained from celestial mechanics and occultation phenomena."

Given that, it is presumed that they were measuring dust along the way since it was instrumented to do that. pparently they've decided that dust wasn't the problem. Mr.Vee

@FKIProfessor - 

Yes, THAT question IS the question. If we do not have an alternate means of determining that there was a problem and if don't understand the cause of the aberration nor able to predict its magnitude, then we will have a hard time getting an "exact position" even though the variation measured is small. Because that variation seems to be small we would know its "vicinity" but an exact position would be impossible. I would propose that the alternate means of determining this is a date/time stamp on the data comparing the reported coordinates and the expected coordinates. The anomaly would show up at that point.

Another quote from the article...

"Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues — who originally helped uncover the Pioneer anomaly — have discovered that four spacecraft each raced either a tiny bit faster or slower than expected when they flew past the Earth en route to other parts of the solar system."

So there isn't just an anomaly around the Kuiper Belt... this is happening not so far away and we had much better contact with these space probes. Mr.Vee