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2005 Pioneer Anomaly Conference

November 6-10, 2005

 

Nov. 6, 2005

Arrival and Introduction

Greetings from Switzerland! My name is Merek Chertkow. Most of you have never heard or read my name before, unless you had delved deeply into The Planetary Society’s Solar Sail project and remembered my name from among the list of people involved. This time, I'm here in Switzerland to inform and keep you up to date on many of the exciting analyses, conclusions, and new questions formed by scientists from around the world working to understand the Pioneer anomaly. The conference consists of some 15 scientists from France, Canada, Norway, Germany, Portugal, and the U.S.

Throughout the week, on a daily basis, I'll try to introduce and remind you of the different complicated elements involved in understanding the Pioneer’s position, environment, the way in which it communicates with the Earth, and the current modeling techniques that are being used. Keep in mind, there are actually two spacecraft under examination, Pioneer 10 and Pioneer 11. Since the anomaly has been detected by both spacecraft, and because they were engineered as identical twins, most references will be just to "Pioneer". I'll make sure to point out the specific spacecraft when it is important.

Nov. 7, 2005

Day One: the Mood in the Air

Today is a day of introductions. Many of the scientists have never met, and as I have said before, come from different regions of Europe and North America. Communication is not difficult if one can get around the strong accents, but I am sure they think the same thing about me.

What is the Pioneer Anomaly, you ask? In brief, the Pioneer Anomaly is an unexplained deceleration of the spacecraft Pioneer 10 and Pioneer 11 as they exit the solar system. Technically speaking, it is a blue shifted Doppler frequency of 6x10^-9 Hz, which can be interpreted as a deceleration of 8.74x10-10 m/s^2 of the spacecraft away from the sun. If you would like to learn more about the details of the Pioneer anomaly itself you can read "What is a New Physics?" Otherwise, let me continue to describe what is being discussed here in Bern, Switzerland.

Given our understanding of the laws of physics (i.e. gravitational forces, general relativity, and considering the known objects in the solar system) and the health of the spacecraft we cannot explain why it is slowing down. Is it a problem with our understanding of the universe? Do we not understand some effect of the spacecraft itself (like outgassing of something)? Or are our calculations of its position and acceleration wrong? For all space and science enthusiasts hoping to bring science fiction a little closer to reality, hold on to your spaceships, we can’t say we have discovered a new aspect of physics yet. Although scientists are very excited about the possibility that we have stumbled upon a new scientific phenomenon, to be honest, the simplest explanation for the Pioneer anomaly is most probably due to an effect that we understand but have not accounted for. A previous study has made it clear there is an anomaly, but it did not go into depth to find its origin, and so we are here to determine what the next few steps in understanding this abnormality will be.

There are several different aspects of the Pioneer anomaly that can be analyzed: internal and external modeling or calculation methods. "Internal" means everything inside and having to do with the spacecraft itself, such as electrical wires, out-gassing, and thermal radiation due to heat generated by the craft. External effects are those due to the environment such as solar radiation pressure, drag forces due to clouds and dust, gravitational fields from the planets and Kuiper belt objects, and all of the laws of physics. Among the big questions here in Switzerland are whether we fully understand the spacecraft’s environment and whether we are modeling the situation correctly.

Accurate modeling is the key to understating the Pioneer Anomaly. It is, in fact, the only way in which we can understand anything about Pioneer 10 and 11. There are no absolute measurements of their position, speed, or acceleration so we use Doppler data to tell us the relative information about the craft with respect to the Earth. The idea is to compare a detailed model of the craft traveling through a model of the universe to tell us in what state and where we should find Pioneer and compare these models to what Pioneer is actually reporting back in the form of Doppler data.

In addition to the Doppler data, telemetry is sent to tell us something about its current state of health. We must account for voltages, currents, temperatures, thrust durations, and any other mechanical change the craft is instructed to make. JPL’s Slava Turyshev, the primary presenter who has called this conference, believes we must systematically analyze every internal aspect. For example, the spacecraft’s power supply comes from four Radioisotopic Thermoelectric Generators (RTGs), which produce a lot of heat onboard. This heat is transferred to and radiates off of different components  out towards space which gives a very small thrust in the direction opposite from which it radiates. If it is found that this heat is being radiated in the same direction as Pioneers trajectory, the craft will slow down. Does this sound familiar? It should! This is the same direction of effect as the Pioneer Anomaly, but this is just one example, and may not be the correct answer. There are many other reasons and explanations that one could make in order to account for the very tiny acceleration.

After Turyshev’s extensive and highly structured presentation the panel admitted it would like to have a copy of his slides. There is a lot of information to go over and a lot of things to consider. Although the problem is quite large and very complicated this room is obviously full of very intelligent sophisticated minds.

The mood is a very informal and comfortable one. For example, Viktor Toth was presenting on the engineering structure of Pioneer, as he started to discuss the “3-meter reflector antenna dish…” Turyshev cut him off in a playful manner to correct him it was a “2.74-meters dish. No rounding here!” Although Turyshev was playing, the point is, everyone wants to make sure we pay attention to detail as this is the only way we can hope to be sure about anything.

In conclusion for the day, the reason this conference has been called is, in essence, that the same sets of eyes have been looking at the Pioneer anomaly data set for close to thirty years without having found a solution. As I am sure everyone who has worked on any difficult problem knows, sometimes an answer comes from a fresh source. It is Turyshev’s idea that the data received from the spacecraft will be distributed amongst different scientific groups and each will perform an independent analysis.  Thanks to The Planetary Society and its members, this can actually happen!

Nov. 8, 2005

Day Two

As we listen and learn about the Pioneer spacecraft I found an image growing in my head. I picture floating in the cold, dark, and silent vacuum of space, and from my perspective the only sensation I have is the width and an unimaginable distance of all of the small points of light that completely surround me. And then, from the side, a white bowl creeps into view. It has three long tripod-type legs sticking straight out from behind it. This craft looks dead. This is Pioneer 10 at 87 astronomical units away (the Sun only looking like a brighter star). The paint and metal coverings show obvious signs of decay from radiation and micrometeorites; the propellant lines are frozen, and no maneuvers are possible; many of the onboard components have shut down for good due to the decay of its four Snap-19 radioisotope thermal generators (the same ones used on the Apollo missions). But, the power is not completely exhausted and the craft is not quite dead; it is in a coherent mode, which means it just sits there listening for a signal from Earth. On March 4, 2006, assuming it has enough power, we hope to wake it up and ask it for just an ounce more of data—despite early news reports back in 2003 stating we had heard from it for the last time. After that, Pioneer 10 will continue on its path, never aligning, in just the right way, to talk to us again. We are not sure what to expect, if we can expect anything, but every bit of information we can obtain is vital to discovering the source of the Pioneer anomaly. This will be the very last chance of ever hearing from Pioneer 10 again.

As for Pioneer 11, its last signal was received on September 30, 1995. It will not be heard from again.

Turyshev does not really think Pioneer 10 will reciprocate with a signal though other participants in the conference, such as Viktor Toth (who is Turyshev’s independent collaborator from Canada), have higher hopes.

The good news: The previous analysis of Pioneer was performed on a data set from 1987 to 1998, but we now have an additional set covering 15 years before this span, and an additional 4 years up to 2002!! Turyshev and John Anderson, also of JPL, with financial support from The Planetary Society were able to save this additional information from simply being thrown in the dumpster! I know what you must be thinking! I can’t believe it either! In sum, we now have 40 gigabytes of data which spans from 1972 to 2002 (the last time we heard from Pioneer 10). Although it is small in comparison to the Gigabyte of information Cassini sends home every day, the time span of 30 years makes it the longest analysis project ever attempted!

Forty Gigabytes still make a large amount of information to work through. To explain, 40 Gigabytes is equivalent to 60,000 data points from Pioneer 10 spanning in time: 1973-2002, and in distance: 4-87 AU; PLUS(!) 50,000 data points from Pioneer 11 spanning in time: 1974-1994, and in distance: 4-33 AU. I am blown away in amazement when I think about performing calculations on the parameters of a spacecraft with the times and distances involved.

What is expected of and from this new data set? We expect nothing, but not in the sense you might think; though we certainly hope to acquire a deeper understanding of, and the reasons behind, the Pioneer anomaly. We do not want any expectations to bias our judgment. One has to remember that we are not looking for an anomaly. Our task is to accurately predict the status of the spacecraft in space and time. It just happens to be turning out that spacecraft is telling us something that our models did not predict. We must go back to the drawing board and carefully reconsider and modify our predictions. In all honesty, we are not sure about the quality of the data, we have not gotten to that stage, and we are not sure if some of the new questions currently being formed are best answered by Doppler data closer to the inner solar system or farther away. It is not doubted, however, that this new set will be an important contribution.

The bad news, as Craig Markwardt from NASA’s Goddard Space Flight Center stated, “We are data-rich, and analyst-poor.” By this he means two things: one, obviously, we do not have a large number of scientists working on the Pioneer anomaly; and two, given the limited number of specialists we do have, the dilemma is knowing the best angle of attack. Despite these obstacles, the important thing is now we are data rich, something that wasn’t true just a few months ago.  We have a new data set from which we can ask completely new questions and see what answers it provides.

Today we heard from three speakers who have each performed an independent analysis of the early data set—before it was complete: Craig Markwardt from NASA/GSFC, Oysten Olsen from the University of Oslo in Norway, and Stephen Theil from ZARM at the University of Bremen in Germany.

Here is a lightly technical example of the kind of input from the different participants: Turyshev, Oysten and Theil independently paid particular attention to determining the anomaly within a three part division of the time span from 1987 to 1990. The first segment was when the Pioneer 10 spacecraft was in its normal spin state, the middle section is a decline in the spin rate from an unconfirmed cause (an indication of a tank leak is the primary suspect), and the third segment is when the spin rate becomes constant again. The small but noticeable anomaly values were found from each segment, and during the discussion of these values many questions such as, where they came from, what parameters were included (or excluded), and what type of calculation methods were used, etc., when Markwardt jumped in and declared that he had run two models: one with spin and one without and had found the difference negligible – thus stating that the spacecraft’s axis spin was not a source for the anomaly. Is he right? He may be, but given the lack of accurate systematic considerations in the past plus having several years of new data that have not been analyzed, the only conclusion one can make is that we are not ready to make a conclusion.

As for the structure of the meetings, the presentations are going well over their scheduled times due to many questions concerning the details of the previous analysis and ideas regarding the significant areas that should be considered in the future. These time delays, though cumbersome because we only have a week in which to present a great amount of material, are important steps in learning how to work together from many different angles.

Another feature of the anomaly focused on today is where the acceleration is actually pointed—towards the Sun or towards the Earth. The theoretical physics (the guys most anxious to disprove, or at least modify, Einstein’s theory), want the anomaly to be an effect of the object which produces the largest gravitational field, the Sun.

Where the anomaly is directed is an important result. It was not known back in 1980, when the anomaly was noticed and is still unconfirmed. If it is pointed towards Earth we can quite easily rule out any gravity theory. The question on everyone’s mind is, looking at the new data will we be able to determine the direction. We just don’t know at this point whether that is possible or not. Imagine, as I stated before, the Sun is just another point in the sky. Can we resolve a distinction between the Sun and the Earth? 

I should point out that even though there seem to be hundreds of old questions waiting to be answered and new questions constantly forming, there is not a feeling among the group that we are attempting a daunting or insurmountable task.

Obviously the spacecraft are too far away to be able to inspect in any form other than the data we have received, but wouldn’t it be nice if we had one here, to take apart and test, to see if something physical had gone wrong onboard? I leave you with Moffat’s suggestion: Just steal the engineering replica from the Smithsonian. 

Nov. 9, 2005

Day Three: Pioneer Anomaly Science

9:00 am
It is Slava Turyshev’s gut feeling that the new Doppler data will show the Pioneer anomaly. What he doesn’t know is what the cause will be. His primary focus is to examine the telemetry data and identify the components of thermal force contributions to the spacecraft acceleration. In brief, he would love us to focus on thermal modeling. This includes involve thermal engineers such as Pierre Touboul from ONERA in Chatillon, France or the ZARM group in Germany (Olsen and Theil).

Once the Pioneer Anomaly data can be provided to different groups who wish to work on it, how do we approach the results of the individual groups? How do we compare everyone’s outputs? The main problem Turyshev sees is that not everyone will have the same quality of data analysis. This brings us to the two types of data Turyshev could supply to the teams: (1) raw data, but then everyone would have to develop models and computation abilities, or (2) one set of pre-processed data (from JPL) where all important models have already been taken into account. With the pre-processed data the theoreticians may analyze the residuals without having to labor through the systematics.

The group here in Switzerland is made up of engineers, theoreticians, and mission analysts, and experts at computational methods. About half of us would like to start with raw data and the other half would like to begin at the pre-processed. Dealing with raw data requires a great amount of time and proficiency that some of the participants do not have. The problem with the pre-processed data is that it is biased towards one point of view with regards to what type of modeling is important. Therefore, a compromise will have to be struck. As of this morning, we have not started assigning tasks, but Turyshev hopes to begin this process soon.

12:30 pm
The path of discussion has been what ideas the theoreticians have about the Pioneer anomaly. Today we heard from scientists discussing their predictions for why the Pioneer anomaly can be explained with gravity and other forms of nature.

Serge Reynaud from LKB in Paris discussed the possibility of extending Einstein’s theory of General Relativity (GR) to incorporate the Pioneer anomaly while making it clear that any modification of GR cannot spoil the acceptable gravity tests that have been performed so far. Just as Newton’s theory became a special case of Einstein’s, any new theory needs to incorporate and maintain Einstein’s discoveries while making a more general statement about the laws of physics. In essence, Raynaud sees the Pioneer mission as the largesscale “gravity test” ever carried out, but it may have failed to confirm the known laws of gravity.

Moving on, the question has become: Can the Pioneer anomaly be compatible with a different theory of gravity? The theoretical physicists in the room believe the answer is yes—even though they each have their own ideas as to why.

There is actually a lot of math that would become confusing very quickly so I will simply say that according to Reynaud’s new physics, the Pioneer anomaly depends upon of the squared velocity of Pioneer with respect to the Sun.  More data analysis should help to test this.

2:50 pm
Claus Laemmerzahl from ZARM at the University of Bremen, Germany would like to attempt to explain the Pioneer anomaly based on the theories of dark matter and dark energy. He had first pointed out that the anomaly is on the order of the cosmological expansion, and like the other theoreticians, conventional physics cannot explain the anomaly.

According to Claus Laemmerzahl, the Pioneer anomaly is a real physical effect and if it cannot be related to dark matter and/or dark energy then it must be a systematic mechanical error. As an example of the interaction with members of the panel, Orfeu firmly disagreed with Laemmerzahl in that this theory must be wrong because it does not fit supernova models—claiming that dark energy effects are 11 orders of magnitude smaller than the anomaly, and dark matter effects are about 4 orders of magnitude smaller.

5:10 pm
Moffat’s presentation was fantastic. He was able to give a clear and detailed explanation that not only gave the correct value for the anomalous acceleration, but accurately predicted the anomaly becoming significant around the distance of Saturn. His theory did not include dark matter--which I believe is just a cool name for something we don’t really understand. And most importantly, his theory fits other astronomical observations by accurately agreeing with solar system data and data from the binary pulsar PSR 1913+16, as well as fitting 101 galaxy rotation curves and galaxy cluster data (the largest fit to date). Moffat is also a realist; he stated that you have to fit everything with a theory. If you can’t fit just 10 galaxies out of the hundreds you are considering, you have to quit.

7:00 pm
In conclusion today, it was decided that we should start planning to break up into groups and figure out who will work in what teams and what the primary investigation of each team will be. Tomorrow, I expect we will form small working groups to decide what is possible and what type of help the individual members of this conference would like to contribute.

Nov. 10, 2005

Day Four: Pioneer Anomaly Science

I should provide an update to the number of scientists and engineers attending the conference. Not everyone can be here for all five days. Some are leaving early and others are arriving late in the week, but in total, there have been about 25 scientists.

9:00 am
Today we began with a summary from Serge Reynaud on the requirements of a longer-term mission to try re-observing the Pioneer anomaly. The idea is a Deep Space Gravity Probe.

Orfeu Bertolami, who usually has the most critical eye among the panel, suggested a solar sail as a vehicle to re-test for the anomaly! He argues a solar sail is useful in completing these mission goals:

  • The ability to build a noise-free spacecraft to confirm and characterize the Pioneer anomaly (noise minimization would allow the anomaly to stand out).
  • Provide us with the opportunity to test new propulsion technology.
  • Investigate the Kuiper belt objects.
  • Perform flybys of Pluto and other objects.
  • Test new ranging technology.

Bertolami highlighted the fact that by completing these goals including having a working, reliable solar sail we would be that much closer to interstellar travel. Viktor Toth asked if a solar sail could be a velocity axis spin-stabilized craft (note: this makes it easier to test for a change in frequency in Doppler data and hence a Pioneer anomaly effect), and I was able to point out to him that this is precisely what The Planetary Society’s Cosmos-1 solar sail mission was designed to do!

10:00 am
Serge Reynaud provided us with a summary of the formalized question and our goals. When we perform a new analysis with the complete data set, the teams should:

  • Study the history of the Pioneer anomaly.
  • Disentangle various possible observations—for example, the magnitudes and directions of the force, time variations, spin contributions)
  • Establish a thermal budget for Pioneer 10 and 11.
  • Scrutinize the Saturn encounter of Pioneer 11.

The team also wants to look for related anomalies in other future space missions and gravity tests. Ulrich Johann from the European Aeronautic Defense and Space Company (EADS) in Germany believes that we have to be realistic when proposing future missions. It is easy to propose a mission that will have the best components, greatest sensitivity, and is able to do whatever we want given current technological capabilities, but missions which aim too high rarely every get past the proposal stage. In order to be taken seriously, a mission has to take into account a reasonable time schedule, as low a budget as possible (while still achieving objective), and it has to consider the capability and constraints of the space agency that will be supporting it.

11:00 am
If the anomaly is a real effect, will other sensitive missions be affected? Denis Defrere from Astrophysics and Geophysics Institute of Liege in Belgium gave a presentation on the Laser Interferometer Space Antenna (LISA) project aimed to launch in 2014. Its primary mission is to detect gravitational waves, but there was discussion whether the Pioneer anomaly could either be a problem for their measurements, or something that could be detected by their measurements.

2:30 pm
Andreas Rathke, also from EADS, created a study to consider what type of missions we want to look at in the future to detect the Pioneer anomaly. In essence, what missions currently in progress or production can we use to test the anomaly with no or little modification? The key, he says, is an inexpensive package. Here are the characteristics of a mission that will enable an anomaly test (here we go with a list again).

  • The overall acceleration systematics must be known (including thermal modeling) to better precision than the magnitude of the anomaly effect.
  • We need a long ballistic arc in which the anomaly will not be overwhelmed by thruster activity.
  •  [Not sure what you mean]We need a highly eccentric orbit with high heliocentric radial velocity (the theorists really like this one)
  • We do not require a specific position in the Solar system (for example, Pioneer 10 and 11 go in opposite directions at different inclinations, but the anomaly is found in both), except that it be far enough out that other effects from the Sun don’t overwhelm the Pioneer anomaly effect.
  • There is no requirement on rotational state of the spacecraft.

We could not perform an anomaly test on a future mission if we have to:

  • Add significant mass to a mission
  • Add mission risk
  • Impair the primary mission goal

I do not know if the panel just has a lot of lists today or if I am just in the mood for reporting them…Back to the point. We can only allow system-design adaptations which will cause a low impact.

5:00 pm
Turyshev introduced the possibility of working with New Horizons, NASA’s Pluto-Kuiper belt mission scheduled to launch on January 11, 2006. The Pioneer anomaly investigation team was invited to come up with a thermal model of the New Horizons spacecraft. New Horizons was developed very rapidly on a very small budget. New Horizons was developed so quickly in order to catch the small launch period that is available to get a Jupiter fly by on the way to Pluto, which cuts flight time by a few years.

New Horizons is a great mission for us to look at; they have a spin-stabilized craft, the Doppler data will be very good (not as good as Cassini, but better than Pioneer), and it will be going out to Pluto (remember we found the Pioneer anomaly at the distance of Saturn)! As Turyshev put it, this is a once in a lifetime opportunity.
Sounds great, right?! Unfortunately, the funding for New Horizons is already limited and we will have to bring our own funding, as well as figuring out the study itself.  So, time will tell if this works out. 

6:00 pm
In summary, the experimentalists have to reanalyze the data to obtain more accurate results to determine if the anomaly is real or not; if it is, the theorists can then work on a new model of physics to try explaining why the anomaly exists. As of now, the following is my final list (I promise) of the major sources of acceleration uncertainty the experimentalists will be scrutinizing until we meet again.

  • Thrust history uncertainty
  • Fuel leaks
  • Heat from spacecraft bus
  • Heat from RTGs
  • RTG helium outgassing
  • Radio-beam force
  • Solar radiation pressure

Tomorrow is officially the last day of the conference. I will be leaving in the morning and will not be here. Fortunately, we have gotten a great amount of work done and seem to have concluded early. Thus, tomorrow will be a very brief summary/conclusion with only about seven people attending. By the afternoon they should be touring the Einstein museum—which I was fortunate enough to visit earlier in the week. I hope to have given you a clear understanding of what the Pioneer anomaly investigation groups are thinking, what their hopes are, and what they desire to understand, but most importantly, how productive we have been here at the International Space Science Institute in Switzerland. I will continue to work on this at The Planetary Society in collaboration with Turyshev at JPL, and I may provide occasional updates as new, significant results are produced.