CV: Farewell, Pioneer Anomaly?

[bystander]

Farewell, Pioneer Anomaly?
Discover Blogs | Cosmic Variance | Sean Carroll | 2010 Dec 15

Here’s an excellent article in Popular Science about the Pioneer anomaly. The Pioneer spacecraft, launched in the early 1970′s, have been moseying through the outer regions of the Solar System for quite some time now. But a careful analysis of tracking data indicated that the acceleration of the two spacecraft didn’t quite match what we’d expect from gravity; there appears to be an anomalous acceleration, nearly constant over time and pointing toward the Sun. Many new-physics explanations have been proposed, but it’s always been a difficult scenario to master; it’s very hard to imagine a new force that would account for the Pioneer data but not also show up in observations of the outer planets. (The Voyager spacecraft aren’t as useful for this purpose, as they are guided by tiny thrusters that overwhelm the signal, while the Pioneers float freely and are pointed using gyroscopes.)

The most likely explanation has always been that we didn’t completely understand the spacecraft, or the tracking system. Indeed, it’s been recognized for a while that a small imbalance in how the spacecraft radiated heat could account for the acceleration — but that imbalance didn’t seem to be supported by what we knew about the vessels. That may be changing, however. The Popular Science article is a little cagey, but it mentions a new and unprecedentedly thorough analysis by Viktor Toth and Slava Turshyev that should be coming out soon. Here is as much as they would let on:

• Five years have passed. Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10^-10 m/s², and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

Doesn’t look good for people who prefer to imagine that wild new physics is responsible. Not that they will go away — the power of wishful thinking is strong. You can already hear them staking out territory, even before the new report comes out:

• Other physicists are more combative. “Heat? That’s simply not the right explanation. They are wrong,” commented Johan Masreliez, an independent researcher in Washington who supports the expanding spacetime model of cosmology, for which it is crucial that the value of the Pioneer anomaly equals c times H. “But then I’m biased,” he added.

Even if the new analysis gives a very sensible and believable account of the Pioneer anomaly in terms of very ordinary physics, expect the true believers to hang on for years to come. The rest of us will move on — at least until the next exciting anomaly pops up.

The Pioneer Anomaly Resolved?
Centauri Dreams | Notes & Queries | Paul Gilster | 2010 Dec 17

8.74 x 10^-10 m/s² isn’t much, but it’s an apparent Sun-ward acceleration sufficient to throw the paths of our Pioneer spacecraft off by a few hundred miles from where they ought to be each year. Noticing the effect in 1980, astronomer John Anderson, who was leading the analysis of Pioneer Doppler ranging data as part of a study of gravitational effects in the outer Solar System, came to the conclusion that outgassing from the spacecraft thrusters was responsible, but the effect persisted longer than it should and a whole range of alternate theories soon came into play after Michael Martin Nieto (Los Alamos National Laboratory) began to study the anomaly in terms of modified Newtonian dynamics (MOND).

The background is given in a fine article by Natalie Wolchover for PopSci. What accounted for Nieto’s fascination was the fact that the value of the anomaly almost exactly equaled the speed of light multiplied by the Hubble constant. At that point, with the possibility that the Pioneers were telling us something fundamental about physics, the Pioneer anomaly took on a life of its own. The discovery of dark energy in the same year that Anderson, Nieto and Slava Turyshev announced their findings about the Pioneer acceleration in Physical Review Letters only added to the interest, and hundreds of papers, many but hardly all on MOND notions, followed.

Were the Pioneer probes measuring the cosmic expansion whose effects are now thought to be intertwined with dark energy? It was one amongst a sea of possibilities. Wolchover’s article describes how Viktor Toth, running an independent analysis using home computers, became skeptical of the earlier work of Anderson and Turyshev and later, with Turyshev, became instrumental in saving the 30-plus years of Pioneer Doppler data and logbooks. With the help of a retired Pioneer mission control engineer named Larry Kellogg, the two acquired Pioneer telemetry data and went back to work from scratch on a much more thorough analysis.

That was five years ago. The result:

• Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10^-10 m/s², and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

If the Pioneer acceleration declines with time, it’s obviously not the constant force it was originally thought to be. The question of decay in that acceleration, and whether the acceleration is indeed in the direction of the Sun or elsewhere, is still open, and Toth and Turyshev are planning to supplement their recently published review of the phenomenon with a forthcoming publication that recounts their latest work. Wolchover thinks the duo have become convinced that thermal effects aboard the spacecraft themselves are the cause of the anomaly, but Turyshev won’t reveal the results, telling the writer only, “Physics as we know it worked well.”

The Pioneer Anomaly - Slava G. Turyshev, Viktor T. Toth

• arXiv.org > gr-qc > arXiv:1001.3686 > 20 Jan 2010 (v1), 19 Aug 2010 (v2)
  Living Reviews in Relativity 13 (2010) 4 (online)
  
  Abstract: Radio-metric Doppler tracking data received from the Pioneer 10 and 11 spacecraft from heliocentric distances of 20-70 AU has consistently indicated the presence of a small, anomalous, blue-shifted frequency drift uniformly changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was interpreted as a constant sunward deceleration of each particular spacecraft at the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. In this review, we summarize the current knowledge of the physical properties of the anomaly and the conditions that led to its detection and characterization. We review various mechanisms proposed to explain the anomaly and discuss the current state of efforts to determine its nature. A comprehensive new investigation of the anomalous behavior of the two Pioneers has begun recently. The new efforts rely on the much-extended set of radio-metric Doppler data for both spacecraft in conjunction with the newly available complete record of their telemetry files and a large archive of original project documentation. As the new study is yet to report its findings, this review provides the necessary background for the new results to appear in the near future. In particular, we provide a significant amount of information on the design, operations and behavior of the two Pioneers during their entire missions, including descriptions of various data formats and techniques used for their navigation and radio-science data analysis. As most of this information was recovered relatively recently, it was not used in the previous studies of the Pioneer anomaly, but it is critical for the new investigation.

The Pioneer Anomaly, a 30-Year-Old Cosmic Mystery, May Be Resolved At Last
Popular Science | Natalie Wolchover | 2010 Dec 15

What is the mystery force slowing down the Pioneer spacecraft? Do we finally know the answer?

[bystander]

Gravity, Working As Usual
Discover Blogs | Cosmic Variance | Julianne Dalcanton | 2011 Mar 31

I am in absolutely no position to judge the technical execution of this work, but a group has posted a possible solution to the “Pioneer Anomaly” on the Physics/Astronomy ArXiV server (http://xxx.lanl.gov/abs/1103.5222).

For those who haven’t been following along at home, there appear to be subtle unexpected Sun-ward accelerations (i.e. higher than expected decelerations) seen in the Pioneer 10 and 11 spacecraft while leaving the Solar System. Sean posted an earlier discussion of the anomaly and a possible reported solution that does not involve modifying gravity. However, this latest paper is by a different group, and posits that reflections within the spacecraft are enough to explain the discrepancies. There’s a nicer write-up than this one at the Technology Review Physics ArXiV blog.

The Pioneer Anomaly Resolved?
Centauri Dreams | Paul Gilster | 2011 Apr 01

The fascination of the so-called ‘Pioneer anomaly’ is that it offers the possibility of new physics, an apparently constant acceleration on the Pioneer 10 and 11 probes with a value of (8.74 ± 1.33) × 10⁻¹⁰ m/s² being something that we can’t easily explain. Equally useful is the chance the Pioneer anomaly gives us to validate current physical models by figuring out how we might explain this acceleration through hitherto unsuspected processes, perhaps aboard the spacecraft itself. Either way you look at it, the Pioneer anomaly has deserved the attention it has received, and now a new paper emerges to take a crack at resolving the issue once and for all.

Frederico Francisco (Instituto Superior Técnico, Lisbon) and colleagues have revisited the question of whether heat that is emitted and reflected aboard the spacecraft could account for the anomalous acceleration. Francisco’s team had accounted for between 33% and 67% of the acceleration in a thermal model they developed in 2008. The new paper builds on this earlier work, with a methodology based on a distribution of point-like radiation sources that can model the thermal radiation emissions of the spacecraft. The authors then deploy a method called ‘Phong Shading’ that is commonly used to render the illumination of surfaces in 3D computer graphics. This allows them to study how heat effects can be reflected off the various parts of the spacecraft.

I referred to the acceleration as ‘apparently constant’ above, but the authors take pains to note that we haven’t fully characterized the acceleration. In fact, one analysis of the flight data shows that, given the data we have, both a constant acceleration and one with a linear decay of a period greater than fifty years are compatible with the data. This comes into play as the team tests for the constancy of the acceleration, as discussed in the paper:

• … a so-called “jerk term” is found to be consistent with the expected temporal variation of a recoil force due to heat generated on board… This is essential if the hypothesis of a thermal origin for the Pioneer anomaly is to be considered, as such [a] source would inevitably lead to a decay with at least the same rate as the power available onboard. Possible causes for an enhanced decay include e.g. degradation of thermocouples, stepwise shutdown of some systems and instruments, etc.

With this in mind, the authors go to work looking at thermal radiation and the force it can bring to bear on a surface, using Phong Shading to model the reflection of this radiation off the various other surfaces of the Pioneer probes. Radiation facing outwards, for example, radiates directly into space with an effect that cancels out. But radiation emitted toward the center of the spacecraft is reflected by the high-gain antenna and the main equipment compartment. The trick is to weigh these effects in terms of the acceleration. The method gives “a simple and straightforward way of modeling the various components of reflection…,” according to the paper, and one that accounts for the effect of thermal radiation on different parts of the spacecraft.

The result: The Phong shading method confirms earlier work suggesting that the Pioneer anomaly results from heat effects aboard the spacecraft. It also offers a method with which to study similar effects aboard other spacecraft. The authors explain:

• … the acceleration arising from thermal radiation effects has a similar order of magnitude to the constant anomalous acceleration reported [in a study of the anomaly published in 2002]. We believe that the chosen approach is most adequate for the study of this particular problem, taking into account all its specific characteristics. Moreover, this Phong shading method is well suited for future studies of radiation momentum transfer in other spacecraft.

And the paper concludes:

• With the results presented here it becomes increasingly apparent that, unless new data arises, the puzzle of the anomalous acceleration of the Pioneer probes can finally be put to rest.

This is a useful result, and one that will now be scrutinized by the wider community. If its conclusions are accepted, we will have made a step forward in identifying an effect that may need to be taken into account in future spacecraft operations. Just as important, we’ll have been able to rule out a line of investigation that seemed to open a door into new physics, meaning that the analysis of the Pioneer Anomaly, now more than a decade old, has born fruit. This is exactly what good science should do, and while we might hope for breakthroughs into new theories, anomalies like these are just as valid as ways of testing and verifying accepted physical laws.

Pioneer Anomaly Solved By 1970s Computer Graphics Technique
Technology Review | The Physics arXiv Blog | 2011 Mar 31

A new computer model of the way heat is emitted by various parts of the Pioneer spacecraft, and reflected off others, finally solves one of the biggest mysteries in astrophysics.

During the last decade or so, the Pioneer Anomaly has become one of the great unsolved puzzles in astrophysics.

The problem is this. The Pioneer 10 and 11 spacecraft were launched towards Jupiter and Saturn in the early 1970s. After their respective flybys, they continued on escape trajectories out of the Solar System, both decelerating under the force of the Sun's gravity. But careful measuremenrs show that the spacecraft are slowing faster than they ought to, as if being pulled by an extra unseen force towards the Sun.

This deceleration is tiny: just (8.74±1.33)×10⁻¹⁰ ms⁻². The big question is where does it come from.

Spacecraft engineers' first thought was that heat emitted by the spacecraft could cause exactly this kind of deceleration. But when they examined the way heat was produced on the craft, by on board plutonium, and how this must have been emitted, they were unable to make the numbers add up. At most, thermal effects could account for only 67 per cent of the deceleration, they said.

That led to a host of other ideas some of which I've covered in this blog. For example, last year we looked at work ruling out the possibility that gravity could be stronger at these distances, since we ought to be able to see a similar effect on the orbit of other distant objects such as Pluto.

Now Frederico Francisco at the Instituto de Plasmas e Fusao Nuclear in Lisbon Portugal, and a few pals, say they've worked out where the thermal calculations went wrong.

These guys have redone the calculations using a computer model of not only how the heat is emitted but how it is reflected off the various parts of the spacecraft too. The reflections turn out to be crucial.

Previous calculations have only estimated the effect of reflections. So Francisco and co used a computer modeling technique called Phong shading to work out exactly how the the emitted heat is reflected and in which direction it ends up travelling.

Phong shading was dreamt up in the 1970s and is now widely used in many rendering packages to model reflections in three dimensions. It was originally developed to handle the reflections of visible light from 3D objects but it works just as well for infrared light, say Francisco and co.

In particular, Phong shading has allowed the Portuguese team to include for the first time the effect of heat emitted from a part of the spacecraft called the main equipment compartment. It turns out that heat from the back wall of this compartment is reflected from the back of the spacecraft's antenna (see diagram above).

Since the antenna points Sunward, towards Earth, reflections off its back would tend to decelerate the spacecraft. "The radiation from this wall will, in a first iteration, reflect off the antenna and add a contribution to the force in the direction of the sun," say Francisco and co.

Lo and behold, this extra component of force makes all the difference. As Francisco and co put it: "With the results presented here it becomes increasingly apparent that, unless new data arises, the puzzle of the anomalous acceleration of the Pioneer probes can finally be put to rest." In other words, the anomaly disappears.

Of course, other groups will want to confirm these results and a team at the Jet Propulsion Laboratory in Pasadena, which has gathered the data on the probes, is currently studying its own computer model of the thermal budgets.

It'll be interesting to see whether they agree. If they do; problem solved. Probably!

Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft - F Francisco et al

• arXiv.org > physics > arXiv:1103.5222 > 27 Mar 2011
  
  Abstract: We present an improved method to compute the radiative momentum transfer in the Pioneer 10 & 11 spacecraft that takes into account both diffusive and specular reflection. The method allows for more reliable results regarding the thermal acceleration of the deep-space probes, confirming previous findings. A parametric analysis is performed in order to set an upper and lower-bound for the thermal acceleration and its evolution with time.

[bystander]

NASA Releases New Pioneer Anomaly Analysis
Technology Review | The Physics arXiv Blog | KFC | 2011 July 20

The mysterious force acting on the Pioneer spacecraft seems to be falling exponentially. That's a strong clue that on-board heat is to blame, says NASA.

---

In the early 1970s, NASA sent two spacecraft on a roller coaster ride towards the outer Solar System. Pioneer 10 and 11 travelled past Jupiter (and Saturn in Pioneer 11's case) and are now heading out into interstellar space.

But in 2002, physicists at NASA's Jet Propulsion Laboratory in Pasadena, noticed a puzzling phenomenon. The spacecraft are slowing down. Nobody knows why but NASA analysed 11 years of tracking data for Pioneer 10 and 3 years for Pioneer 11 to prove it.

This deceleration, the Pioneer anomaly, has become one of the biggest problems in astrophysics. One idea is that gravity is different at theses distances (Pioneers 10 and 11 are now at 30 and 70 AU). That would be the most exciting conclusion.

But before astrophysicists can accept this, other more mundane explanations have to be ruled out. Chief among these is the possibility that the deceleration is caused by heat from the spacecraft's radioactive batteries, which may radiate more in one direction than another.

Back in March, physicists from Europe claimed that a new computer model of heat emission from the spacecraft had finally nailed the problem. This proved that heat was to blame, they said.

NASA, which has its own team looking at this, has kept quiet about this result and today we can see why. Slava Turyshev at JPL and a few pals say they've trawled through JPL's records looking for more data. And they've found it.

These guys say they've been able to double the datasets for both spacecraft. That increases the tracking data for Pioneer 10 to 23 years and Pioneer 11 to 11 years. That's a jump from 20,055 to 41,054 data points for Pioneer 10 and from 10,616 to 81,537 for Pioneer 11.

So what does it show? Firstly, the new data confirms that anomalous deceleration exists.

But it also throws up something interesting. Turyshev and co say there appears to be an exponential drop in the size of the anomalous deceleration over time. It's not easy to see in the data for sure, but there are certainly signs it is there.

That's an important clue. Pioneer 10 and 11 are powered by the radioactive decay of plutonium-238, which of course decays exponentially.

NASA is currently performing its own computer simulation of the way that heat is emitted by the spacecraft to see whether it can explain the new dataset.

All the clues point to the notion that heat can explain the Pioneer anomaly. As Turyshev and co put it: "The most likely cause of the Pioneer anomaly is the anisotropic emission of on-board heat."

So it looks as if NASA is set to agree with the European conclusion and that astronomers will soon be able to put this great mystery to rest once and for all.

Planetary Society Statement on the Pioneer Anomaly
Planetary Society | Charlene Anderson | 2011 July 22

Planetary Society Members have been supporting Slava Turyshev and his colleagues in their scientific quest to solve the famous Pioneer Anomaly. They have just published a peer-reviewed paper that reports on what may be the last step toward the solution. Today, the Society issued a statement on their progress, which you can read below.

We're almost there….

New Data Pushes Pioneer Anomaly to Verge of Solution
Planetary-Society Sponsored Research Aids In Explanation of Mystery

Scientists working with recently recovered data from the Pioneer 10 and 11 missions are closing in on a solution to the famous Pioneer Anomaly. Their just-published results show that the mysterious effect on the two spacecraft is not constant over time, probably indicating that no outside force is acting on the Pioneers, but rather, something inside the spacecraft is to blame.

Slava Turyshev and a team of researchers are publishing an upcoming issue of Physical Review Letters their analysis of radio transmission data from the spacecraft. Their work strengthens the case that the source of the anomaly lies in the spacecraft themselves, not in any mysterious outside force acting on them. The most likely cause is heat generated by spacecraft systems, producing a recoil force.

The Pioneer Anomaly was defined as "anomalous acceleration in the direction of the Sun" or, as seen from Earth, the spacecraft appeared to be slowing down. It was first detected in 1980 by John D. Anderson of the Jet Propulsion Laboratory through his analysis of the Doppler shift in the radio signal from the Pioneers 10 and 11 on their way out of the solar system, after becoming the first spacecraft to fly by Jupiter and Saturn.

Since its discovery, suggested solutions to the Pioneer Anomaly have ranged from such things as the gravity of as-yet undetected bodies in the solar system, dark matter or dark energy, the cosmic expansion, to some sort of New Physics, such as modifications to the theory of gravity. For over 20 years, scientists around the world have been seeking an explanation.

Planetary Society members have been eager to help solve this mystery with their support to the research team and their enthusiasm for pushing the boundaries of what is known. With Society members' backing, Turyshev and his colleagues were able to recover spacecraft data preserved in obsolete formats or once thought lost. This vastly increased the "data arc" for the spacecraft's trajectories, enabling the team to analyze the Pioneers' behavior over many more years than earlier researchers were able to do.

"We recovered more data than we dared dream possible," Turyshev said, "Without the rescue of the Doppler data, we would have been blind, never able to claim the quantitative data we need to solve the anomaly."

Doppler measurements

Over 25 years ago John Anderson noticed that the Pioneers' radio signals drifted slightly from what was expected according to well-understood laws of physics. There was a small "blue shift" toward radio receivers on Earth, the opposite of the famous "red shift" of galaxies that appear to be moving away from our location on Earth.

The early analysis indicated that the anomaly was constant over time. This suggested some force external of the spacecraft was "putting on the brakes," not an on-board system that would slowly be running out of power. With the newly recovered data, Turyshev and colleagues were able to discern that the anomaly was, in fact, decreasing over time, consistent with decaying thermal power on-board the spacecraft.

The most likely suspect behind the acceleration is indeed heat radiating from the Pioneers' power source and leaking from the spacecraft's instruments. Turyshev and colleagues are completing their meticulous study of thermal forces and will soon publish their peer-reviewed final results.

Thermal modeling

Through the radioactive decay of plutonium, radioisotope thermoelectric generators (RTGs) provide the energy spacecraft needed to operate its instruments and communicate with Earth. To communicate from the outer solar system, a spacecraft needs a big antenna, hence the big, parabolic antennas that dominate the profiles of all really-deep-spacecraft.

The analysis of recovered telemetry data indicates that heat from the RTGs reflected off the backside of the big high-gain antenna and helped "push" the spacecraft back toward the sun.

There was another thermal effect at work: heat radiating from the instruments housed inside the spacecraft "bus" was vented through louvers that could be opened or closed as necessary. With the spacecraft "rebuilt" as a computer model for analysis, the team was able to determine that the escaping heat was pointed in the direction of the Pioneer Anomaly, thus slowing the spacecraft on their trajectories away from the sun.

"The recovery of Doppler and telemetry data and the entire effort in thermal analysis would not have happened without the Planetary Society," said Turyshev. "The members provided the money we needed to get started and demonstrated to NASA that the public was definitely interested in solving the mystery. Their interest and strong support made possible our work to solve the Pioneer Anomaly."

Benefits of a Mystery Solved

While solving the Pioneer Anomaly will not lead to a new physics, the work will have benefits in the endeavor of space exploration. Understanding how a spacecraft's flight can be affected by such tiny forces as the recoil force due to heat radiating from power sources and scientific instruments can lead to more accurate spacecraft navigation. This will have a tremendous impact on future mission aiming to search for gravitational waves, testing the fundamental laws of physics, and studying the universe.

The mystery contributed in other ways to modern science by stimulating work on the fundamental principles that govern the physics of objects in space, and in testing how gravity – as described by both Newton's Law of Gravity and Einstein's Theory of General Relativity -- behaves in our solar system.

Bill Nye, Executive Director of the Planetary Society, commented: "What a remarkable business. Slava and his colleagues are analyzing the motions of spacecraft that have flown fantastically far away from us, but not quite as far as we once figured they should fly. So far, it's not new physics; just the surprising subtle push of photons. This kind of diligent analysis would be impossible without the good data that we recovered. I'm looking forward to the next level of this analysis. It will affect spacecraft operations for years to come."

Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets - SG Turyshev et al

• arXiv.org > gr-qc > arXiv:1107.2886 > 14 Jul 2011
  
  Abstract: The Pioneer anomaly is a small sunward anomalous acceleration found in the trajectory analysis of the Pioneer 10 and 11 spacecraft. As part of the investigation of the effect, analysis of recently recovered Doppler data for both spacecraft has been completed. The presence of a small anomalous acceleration is confirmed using data spans more than twice as long as those that were previously analyzed. We examine the constancy and direction of the Pioneer anomaly, and conclude that: i) the data favor a temporally decaying anomalous acceleration (~2•10^-11 m/s²/yr) with an over 10% improvement in the residuals compared to a constant acceleration model; ii) although the direction of the acceleration remains imprecisely determined, we find no support in favor of a Sun-pointing direction over the Earth-pointing or along the spin-axis directions, and iii) support for an early "onset" of the acceleration remains weak in the pre-Saturn Pioneer 11 tracking data. We present these new findings and discuss their implications for the nature of the Pioneer anomaly.

Plutonium Is Hot Suspect in Pioneer Spacecraft Mystery
Wired Science | Duncan Geere, Wired UK | 2011 July 26

[neufer]

• "Pioneers! O Pioneers!" by Walt Whitman
  ............................................
  Come my tan-faced children,
  Follow well in order, get your weapons ready,
  Have you your pistols? have you your sharp-edged axes?
  Pioneers! O pioneers!
  
  For we cannot tarry here,
  We must march my darlings, we must bear the brunt of danger,
  We the youthful sinewy races, all the rest on us depend,
  Pioneers! O pioneers!
  
  O you youths, Western youths,
  So impatient, full of action, full of manly pride and friendship,
  Plain I see you Western youths, see you tramping with the foremost,
  Pioneers! O pioneers!
  
  Have the elder races halted?
  Do they droop and end their lesson, wearied over there beyond the seas?
  We take up the task eternal, and the burden and the lesson,
  Pioneers! O pioneers!
  
  All the past we leave behind,
  We debouch upon a newer mightier world, varied world,
  Fresh and strong the world we seize, world of labor and the march,
  Pioneers! O pioneers!
  
  We detachments steady throwing,
  Down the edges, through the passes, up the mountains steep,
  Conquering, holding, daring, venturing as we go the unknown ways,
  Pioneers! O pioneers!
  
  We primeval forests felling,
  We the rivers stemming, vexing we and piercing deep the mines within,
  We the surface broad surveying, we the virgin soil upheaving,
  Pioneers! O pioneers!
  
  Colorado men are we,
  From the peaks gigantic, from the great sierras and the high plateaus,
  From the mine and from the gully, from the hunting trail we come,
  Pioneers! O pioneers!
  
  From Nebraska, from Arkansas,
  Central inland race are we, from Missouri, with the continental blood intervein'd,
  All the hands of comrades clasping, all the Southern, all the Northern,
  Pioneers! O pioneers!
  
  O resistless restless race!
  O beloved race in all! O my breast aches with tender love for all!
  O I mourn and yet exult, I am rapt with love for all,
  Pioneers! O pioneers!
  
  Raise the mighty mother mistress,
  Waving high the delicate mistress, over all the starry mistress, (bend your heads all,)
  Raise the fang'd and warlike mistress, stern, impassive, weapon'd mistress,
  Pioneers! O pioneers!
  
  See my children, resolute children,
  By those swarms upon our rear we must never yield or falter,
  Ages back in ghostly millions frowning there behind us urging,
  Pioneers! O pioneers!
  
  On and on the compact ranks,
  With accessions ever waiting, with the places of the dead quickly fill'd,
  Through the battle, through defeat, moving yet and never stopping,
  Pioneers! O pioneers!
  
  O to die advancing on!
  Are there some of us to droop and die? has the hour come?
  Then upon the march we fittest die, soon and sure the gap is fill'd.
  Pioneers! O pioneers!
  
  All the pulses of the world,
  Falling in they beat for us, with the Western movement beat,
  Holding single or together, steady moving to the front, all for us,
  Pioneers! O pioneers!
  
  Life's involv'd and varied pageants,
  All the forms and shows, all the workmen at their work,
  All the seamen and the landsmen, all the masters with their slaves,
  Pioneers! O pioneers!
  
  All the hapless silent lovers,
  All the prisoners in the prisons, all the righteous and the wicked,
  All the joyous, all the sorrowing, all the living, all the dying,
  Pioneers! O pioneers!
  
  I too with my soul and body,
  We, a curious trio, picking, wandering on our way,
  Through these shores amid the shadows, with the apparitions pressing,
  Pioneers! O pioneers!
  
  Lo, the darting bowling orb!
  Lo, the brother orbs around, all the clustering suns and planets,
  All the dazzling days, all the mystic nights with dreams,
  Pioneers! O pioneers!
  
  These are of us, they are with us,
  All for primal needed work, while the followers there in embryo wait behind,
  We to-day's procession heading, we the route for travel clearing,
  Pioneers! O pioneers!
  
  O you daughters of the West!
  O you young and elder daughters! O you mothers and you wives!
  Never must you be divided, in our ranks you move united,
  Pioneers! O pioneers!
  
  Minstrels latent on the prairies!
  (Shrouded bards of other lands, you may rest, you have done your work,)
  Soon I hear you coming warbling, soon you rise and tramp amid us,
  Pioneers! O pioneers!
  
  Not for delectations sweet,
  Not the cushion and the slipper, not the peaceful and the studious,
  Not the riches safe and palling, not for us the tame enjoyment,
  Pioneers! O pioneers!
  
  Do the feasters gluttonous feast?
  Do the corpulent sleepers sleep? have they lock'd and bolted doors?
  Still be ours the diet hard, and the blanket on the ground,
  Pioneers! O pioneers!
  
  Has the night descended?
  Was the road of late so toilsome? did we stop discouraged nodding on our way?
  Yet a passing hour I yield you in your tracks to pause oblivious,
  Pioneers! O pioneers!
  
  Till with sound of trumpet,
  Far, far off the daybreak call--hark! how loud and clear I hear it wind,
  Swift! to the head of the army!--swift! spring to your places,
  Pioneers! O pioneers!

[bystander]

Pioneer Anomaly Solved!
Planetary Society | Bruce Betts | 2012 Apr 19

With the latest piece of the puzzle just published in a scientific journal, a solar system mystery that has perplexed people for more than 20 years has been solved, truly thanks to the support of Planetary Society members. That mystery is the "Pioneer Anomaly," an anomalous acceleration that affected the two Pioneer spacecraft as they left the solar system.

Pioneers 10 and 11 were launched in the early 1970's. As they traveled away from the Sun, they slowed down. Most of this slowing was expected, a result of the gravitational pull of the Sun and other massive objects in the solar system. But even when everything in the solar system whose mass could have any effect on the Pioneers was accounted for, both spacecraft were found to be slowing more than expected. The excess slowing was very tiny, but measurable.

[i][b]Temperature sensors within Pioneer 10[/b] Inside Pioneer 10's equipment and instrument compartments were six sensors that measured the temperature of the spacecraft through time. The temperature readings were reported back to Earth as a part of Pioneer 10's regular radio transmissions throughout the mission. These temperature readings provided boundary conditions for the thermal model of the spacecraft. (Credit: NASA/JPL/Slava Turyshev)[/i]

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Over the course of the past two decades, all sorts of solutions have been proposed, some of which invoked exotic "new" physics. In the end, recovery of more data and years of painstaking work have shown that no such exotic solution is necessary, but rather that anisotropic (big word for not-symmetric-in-all-directions) thermal radiation (big words for heat) can explain the mystery. This solution had already been suggested, and examination of the problem over time had made it seem increasingly likely, but only careful analyses could check whether anisitropic radiation could explain the anomaly. The latest piece of this analysis appears in a new scientific article by Slava Turyshev and colleagues.

The only way to solve this mystery was to look at much more data than had previously been available. That is where Planetary Society members stepped in. A few years ago, Slava Turyshev and his colleagues at the Jet Propulsion Laboratory were in desperate need of funding to help them do just that. With funds supplied by our members, Turyshev successfully chased down data from a number of sources. This was not an easy (or quick) task. These missions lasted for more than 30 years. Imagine all the people, computing formats, and hardcopy and electronic storage devices involved over that period, and you'll start to get an idea of the problem.

As Slava mentioned to us before, "We recovered more data than we dared dream possible. Without the rescue of the Doppler data, we would have been blind, never able to claim the quantitative data we need to solve the anomaly. The recovery of Doppler and telemetry data and the entire effort in thermal analysis would not have happened without the Planetary Society."

After they recovered the data, they had decades of Doppler data to analyze. That told them the true nature of the acceleration – the anomaly -- and how it acted over time including that it varied, rather than staying constant. See this discussion for more details on their Doppler results as well as more background on the Pioneer Anomaly.

To really nail down whether a thermal explanation alone could explain the anomaly required detailed thermal modeling of the spacecraft, and that is the focus of the new paper. This also could not have been accomplished without the saving of data facilitated by Planetary Society members. That process turned up spacecraft schematics used to construct the model, but also turned up data on spacecraft temperatures during the mission. The latter allowed comparison of real temperatures in a few locations with the model.

Why was the thermal emission from the spacecraft anisotropic and slowing the spacecraft down? First of all, because the Pioneer spacecraft were spin-stabilized and almost always pointed their big dishes towards Earth. Second of all, because two sources of thermal radiation (heat) were then on the leading side of the spacecraft. The nuclear power sources, more formally Radioisotope Thermoelectric Generators (RTG), emitted heat towards the back side of the dishes. When the dishes reflected or re-radiated this heat, it went in the direction of travel of the spacecraft. Also, the warm electronics box for the spacecraft was on the leading side of the spacecraft, causing more heat to spill that direction. Photon pressure, the same type of thing used in solar sailing, then preferentially pushed against the direction of travel, causing a tiny, but measurable, deceleration of the spacecraft – the Pioneer Anomaly.

These results once emphasize three things to me: the power of more data, the power of careful scientific analysis, and the power of Planetary Society members getting involved at critical times. In addition to providing the solution to a long-term solar system mystery, the technical results of these studies will be useful for planning the details of future spacecraft navigation.

Support for the thermal origin of the Pioneer anomaly - Slava G. Turyshev et al

• arXiv.org > gr-qc > arXiv:1204.2507 > 11 Apr 2012

[neufer]

Since its discovery, suggested solutions to the Pioneer Anomaly have ranged from such things as the gravity of as-yet undetected bodies in the solar system, dark matter or dark energy, the cosmic expansion, to some sort of New Physics, such as modifications to the theory of gravity. For over 20 years, scientists around the world have been seeking an explanation.

Farewell possible new physics.

[Chris Peterson]

Farewell possible new physics. :cry:

I think there's plenty of exciting new physics to be worked out, without throwing a monkey wrench into our current understanding of things.

[neufer]

Click to play embedded YouTube video.

Farewell, Pioneer Anomaly?
Discover Blogs | Cosmic Variance | Sean Carroll | 2010 Dec 15

Even if the new analysis gives a very sensible and believable account of the Pioneer anomaly in terms of very ordinary physics, expect the true believers to hang on for years to come. The rest of us will move on — at least until the next exciting anomaly pops up.

[emc]

Twenty years?

Like Bystander points out, “The need for mystery is greater than the need for an answer. — Ken Kesey”

Does this mean their coming back? Bummer, where's the romance in that!

[neufer]

Does this mean their [sic] coming back?

The plutonium-238 in the Pioneers's radioisotope thermoelectric generators (RTG) has a half-life of 87.74 years such that the total thermal deceleration will only amount to about 3.5 m/s. (They aint comin back.}

3.5 m/s = 8.74 x 10^-10m/s² x 31,536,000 s x 87.74/ln(2)

[emc]

Does this mean their [sic] coming back?

The plutonium-238 in the Pioneers's radioisotope thermoelectric generators (RTG) has a half-life of 87.74 years such that the total thermal deceleration will only amount to about 3.5 m/s. (They aint comin back.}

3.5 m/s = 8.74 x 10^-10m/s² x 31,536,000 s x 87.74/ln(2)

Not only did I leave out a key "smilie" , I trusted Word to correct my bad spelling and grammar.

It’s all in the timing… and I need to take more of it.

Thanks for the kind and funny scientific response sir!

[bystander]

Study Finds Heat is Source of 'Pioneer Anomaly'
NASA | JPL-Caltech | Ames Research Center | 2012 July 17

[attachment=0]667318main_jpl_pioneer_galaxy_FULL.jpg[/attachment][/i]

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The unexpected slowing of NASA's Pioneer 10 and 11 spacecraft - the so-called "Pioneer Anomaly" - turns out to be due to the slight, but detectable effect of heat pushing back on the spacecraft, according to a recent paper. The heat emanates from electrical current flowing through instruments and the thermoelectric power supply. The results were published on June 12 in the journal Physical Review Letters.

"The effect is something like when you're driving a car and the photons from your headlights are pushing you backward," said Slava Turyshev, the paper's lead author at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It is very subtle."

Launched in 1972 and 1973 respectively, Pioneer 10 and 11 are on an outward trajectory from our sun. In the early 1980s, navigators saw a deceleration on the two spacecraft, in the direction back toward the sun, as the spacecraft were approaching Saturn. They dismissed it as the effect of dribbles of leftover propellant still in the fuel lines after controllers had cut off the propellant. But by 1998, as the spacecraft kept traveling on their journey and were over 8 billion miles (13 billion kilometers) away from the sun, a group of scientists led by John Anderson of JPL realized there was an actual deceleration of about 300 inches per day squared (0.9 nanometers per second squared). They raised the possibility that this could be some new type of physics that contradicted Einstein's general theory of relativity.

In 2004, Turyshev decided to start gathering records stored all over the country and analyze the data to see if he could definitively figure out the source of the deceleration. In part, he and colleagues were contemplating a deep space physics mission to investigate the anomaly, and he wanted to be sure there was one before asking NASA for a spacecraft.

He and colleagues went searching for Doppler data, the pattern of data communicated back to Earth from the spacecraft, and telemetry data, the housekeeping data sent back from the spacecraft. At the time these two Pioneers were launched, data were still being stored on punch cards. But Turyshev and colleagues were able to copy digitized files from the computer of JPL navigators who have helped steer the Pioneer spacecraft since the 1970s. They also found over a dozen of boxes of magnetic tapes stored under a staircase at JPL and received files from the National Space Science Data Center at NASA Goddard Space Flight Center, Greenbelt, Md., and worked with NASA Ames Research Center, Moffett Field, Calif., to save some of their boxes of magnetic optical tapes. He collected more than 43 gigabytes of data, which may not seem like a lot now, but is quite a lot of data for the 1970s. He also managed to save a vintage tape machine that was about to be discarded, so he could play the magnetic tapes.

The effort was a labor of love for Turyshev and others. The Planetary Society sent out appeals to its members to help fund the data recovery effort. NASA later also provided funding. In the process, a programmer in Canada, Viktor Toth, heard about the effort and contacted Turyshev. He helped Turyshev create a program that could read the telemetry tapes and clean up the old data.

They saw that what was happening to Pioneer wasn't happening to other spacecraft, mostly because of the way the spacecraft were built. For example, the Voyager spacecraft are less sensitive to the effect seen on Pioneer, because its thrusters align it along three axes, whereas the Pioneer spacecraft rely on spinning to stay stable.

With all the data newly available, Turyshev and colleagues were able to calculate the heat put out by the electrical subsystems and the decay of plutonium in the Pioneer power sources, which matched the anomalous acceleration seen on both Pioneers.

"The story is finding its conclusion because it turns out that standard physics prevail," Turyshev said. "While of course it would've been exciting to discover a new kind of physics, we did solve a mystery."

Support for the thermal origin of the Pioneer anomaly - Slava G. Turyshev et al

• Physical Review Letters 108(24) 241101 (12 June 2012) DOI: 10.1103/PhysRevLett.108.241101
  arXiv.org > gr-qc > arXiv:1204.2507 > 11 Apr 2012

Case Closed on the Pioneer Anomaly
Universe Today | Nancy Atkinson | 2012 July 18

Resolving the Pioneer Anomaly
Centauri Dreams | Paul Gilster | 2012 July 18

http://asterisk.apod.com/viewtopic.php?p=174065#p174065