* Astronomy

According to Michael Nieto of the Los Alamos National Laboratory in New Mexico, the data for Pioneer 10 was not precise enough around the time of its fly-by of Jupiter to indicate whether its acceleration problems began with that encounter. But, this may soon be remedied. JPL's Slava Turyshev recently unearthed archived data from Pioneer 10 and 11 and is reconstructing the missions in their entirety, which could help determine whether Pioneer 10's anomaly began with a fly-by too.

"That's what I want to look at more precisely" - Michael Nieto .

The researchers say that while it is possible that an overlooked effect from ordinary physics might account for the anomalies, something more exotic could also be involved. For example, the spacecraft trajectories could be influenced by the presence of dark matter in the solar system. Or maybe the laws of gravity need reworking.
Peter Antreasian, a spacecraft navigation expert at JPL who along with Joseph Guinn first brought attention to the anomalies seen in Galileo and NEAR during their Earth fly-bys, believes that it will require a modified law of gravity or other new physics to explain it. He does not think it is connected to the Pioneer anomaly, since the force behind this seems always to point in the same direction, back towards the sun. In the Earth fly-bys, by contrast, "a directional force such as the Pioneer anomalous force would have been very evident in the radiometric data in the last few days before the approach". Whatever causes this anomaly seems to make its impact just a few minutes before the closest approach to Earth.
Not everyone is convinced the Earth fly-by anomaly points to new physics. Myles Standish, who calculates trajectories of solar system bodies for JPL, says he feels the Earth fly-by anomaly is almost certainly due to an error in measurement or an incomplete analysis using ordinary physics

Source New Scientist

There's a mystery at the edge of our solar system. Two spacecraft, Pioneers 10 and 11, which were launched to Jupiter and Saturn more than 30 years ago, are hurtling towards the edge of our solar system -- but at a slower than expected rate. Called the "Pioneer Anomaly," the effect of this slowing is small, but measurable, and so far unexplained.

This riddle has sparked an array of possible explanations, ranging from dark matter to spacecraft equipment to - most provocative of all - a new physics.
"More data" is what scientists need to solve the mystery, and more data is what they now possess, thanks to Planetary Society members.

Only a fraction of the Pioneer spacecraft navigational data have ever been analysed to study this anomaly. But much of the more than 30 years of mission data was in disarray, on ancient media, and in danger of being destroyed. That's where The Planetary Society's members stepped in.
Only about 11 years of the Pioneer Doppler data, which measured the spacecrafts' velocity through the Doppler shift of the received frequency of the Pioneer signal, had been analysed, and no solution to the slowdown had been determined. Much of the remaining data was stored on old 7- and 9-track magnetic tapes and needed to be identified, recovered and saved. No NASA funding was available for that task.
The Planetary Society issued an appeal to its worldwide membership and raised the funding needed to recover and validate this trove of information.

"We were happy to come to the rescue when no one else would. Whether the new data show the anomaly to be caused by some mundane effect from the spacecraft itself or lead to a new understanding of physics, the Pioneer Anomaly has been a mystery calling out to be solved." - Bruce Betts, Project Manager of The Planetary Society.

After The Planetary Society initiated the project, the Jet Propulsion Laboratory (JPL) also contributed in-house funds to further support the Pioneer Anomaly team. Scientists and engineers led by Slava G. Turyshev at JPL were able to recover much of the more-than-30-year navigational histories of both spacecraft, including data from their Jupiter and Saturn encounters in the 1970s. The data are now being collected, arranged, validated, and written to modern media and will be provided to teams of scientists to analyse.
Success extended beyond the recovery of the velocity data. Information about the spacecraft themselves, as well as science data, were contained in what are called Master Data Records (MDRs), discovered in storage at NASA Ames Research Centre (which operated the Pioneer spacecraft). Original plans called for that data to be kept for 7 years, but fortunately, many records were turned up in the search for more data. Thanks to Viktor Toth, a software designer from Canada, these telemetry data files are also being collected and arranged, all useful data is being extracted, and they are being written to modern media.

What can these additional data tell scientists? For one thing, MDR data include temperatures measured throughout the spacecraft during the course of the missions. These will be critical for modelling the thermal radiation from the spacecraft, its variations over time, and whether it could help explain the anomaly. Planetary Society college intern Merek Chertkow is beginning to analyse this information, as are various professional scientists.
The Pioneer Anomaly was discovered when John D. Anderson and colleagues at JPL realised that the trajectories of the two spacecraft were deviating from the known laws of motion. After about 30 years of travel, the Pioneer Anomaly has resulted in the spacecraft being about 240,000 miles (the Earth Moon distance) closer to the Sun than we would expect. That may sound like a trivial amount when one considers the Pioneer spacecraft are travelling at 30,000 miles per hour, but scientists were intrigued because no known factor explained the slowdown.

What could be affecting their speed? Many hypotheses have been suggested:

*the interplanetary plasma and solar wind
*thermal recoil force due to heat from the spacecraft's nuclear power sources
*mysterious Dark Matter in the galaxy
*a manifestation of new physics

No hypothesis could be adequately explained by known data, but with the data saved with the help of The Planetary Society, scientists will now have far more information available to help them solve the Pioneer Anomaly.

Source

Study of the anomalous acceleration of Pioneer 10 and 11
Authors: John D. Anderson, Philip A. Laing, Eunice L. Lau, Anthony S. Liu,
Michael Martin Nieto, Slava G. Turyshev

Previous analyses of radio Doppler and ranging data from distant spacecraft in the solar system indicated that an apparent anomalous acceleration is acting on Pioneer 10 and 11, with a magnitude a_P ~ 8 x 10^-8 cm/s^2, directed towards the Sun. Much effort has been expended looking for possible systematic origins of the residuals, but none has been found.

A detailed investigation of effects both external to and internal to the spacecraft, as well as those due to modelling and computational techniques, is provided. The researchers also discuss the methods, theoretical models, and experimental techniques used to detect and study small forces acting on interplanetary spacecraft. These include the methods of radio Doppler data collection, data editing, and data reduction.
There is now further data for the Pioneer 10 orbit determination. The extended Pioneer 10 data set spans 3 January 1987 to 22 July 1998.
(For Pioneer 11 the shorter span goes from 5 January 1987 to the time of loss of coherent data on 1 October 1990.)
With these data sets and more detailed studies of all the systematics, they now give a result, of a_P = (8.74 ± 1.33) x 10^-8 cm/s^2. (Annual/diurnal variations on top of a_P, that leave a_P unchanged, are also reported and discussed.)

ReadMore (PDF)

Very soon, NASA will be dismantling and scrapping its only computer left which is able to access and process the data on its ancient 7- and 9-track magnetic tapes.
The data held on these few hundred tapes contain the complete archive of the first 15 years of all the data returned to Earth by the Pioneer spacecraft which were sent into interstellar space.

This additional and thus far unexamined data (the data after 1988 is available and has already been examined) may hold the key to solving what is considered one of the top problems in physics today, the so called Pioneer anomaly, where the observed trajectory of these spacecraft (and a couple others) deviates noticeably from calculated expectation.
The reason for the anomaly may be as mundane as uneven radiation pressure or escaping thruster fuel or it may be as groundbreaking as a clue to completely new physics, perhaps related to dark matter or dark energy.
The Planetary Society is planning on recovering this data and meticulously examine it to look for something which may have been missed or hidden from current investigations into the phenomenon.
They need money to do this, about $250,000, and are asking for donations to fund the project.
There are no serious proposals to send any more spin-stabilized spacecraft on solar escape trajectories any time in the near future and this is probably the only tenable method we have to directly investigate this mystery in the interim.

https://planetary.org/donations.html