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NASA Space Science

New Theory About the Source of Pioneer Space Probe Deceleration 156

Posted by samzenpus
from the solving-a-mystery dept.
First time accepted submitter deathcow writes "After forty years, a fresh perspective on old Pioneer data leads to new conclusions as to why the Pioneer probes are decelerating. Many theories to the slowing probes have persisted over the years — was it gravity? some type of unforeseen radiation? dark matter? Thanks to the data backup preservation efforts of a NASA Ames Research engineer, mountains of old telemetry data were still available for studying this curious anomaly."
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New Theory About the Source of Pioneer Space Probe Deceleration

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  • by Press2ToContinue (2424598) * on Friday December 07, 2012 @01:41AM (#42212869)

    It's thermal recall force from heat generated by components on Pioneer.

    The article is way too long but here's the essential paragraph:

    "we estimated the magnitude of the thermal recoil force at different times over the course of the Pioneer missions. After matching the model to the Pioneers’ temperature and electrical readings, we found that the spacecraft did experience a sizable thermal recoil force, corresponding to an excess of about 60 W even after 20 years in deep space. The magnitude of the force was still tiny by Earth standards—about the same as the backward push your car experiences in reaction to the photons spit out by its high-beam headlights. The team found that a good half of the force came from heat from the RTGs (radioisotope thermoelectric generators), which bounced off the back of the spacecraft antenna. The other half came from electrical heat from circuitry in the heart of the spacecraft"

    There, you may resume.

    • by Anonymous Coward

      Thanks a lot!

    • Re: (Score:2, Informative)

      by Anonymous Coward

      ... wasn't this already determined, around a year ago?

      • by prefec2 (875483)

        I thought so too. Someone must have a very, very short memory. Or non at all.

        • by skids (119237) on Friday December 07, 2012 @11:17AM (#42215127) Homepage

          Actually it turns out we have a very long memory. We remembered gigabytes of data for several decades, as well as enough data about a machine we built decades ago to model it in excruciating detail, then used it to refine the calculations for a possible explanation for a miniscule discrepency in the speed of a relatively tiny object billions of miles away. I'd say that's pretty incredible.

          Meanwhile most people can't figure out how to remember a secure password. How's that for contrast?

          • Actually it turns out we have a very long memory. We remembered gigabytes of data for several decades, as well as enough data about a machine we built decades ago to model it in excruciating detail, then used it to refine the calculations for a possible explanation for a miniscule discrepency in the speed of a relatively tiny object billions of miles away. I'd say that's pretty incredible.

            Meanwhile most people can't figure out how to remember a secure password. How's that for contrast?

            The crucial difference you seem to be missing is that this data was recorded on some medium. If you write down that secure password you won't forget it, and if you tried to remember all this data about the spacecraft it would be long gone.

          • by prefec2 (875483)

            You know, I was not bashing the scientists. I was pointing out, that those who put the article with the provided teaser on slashdot seem to have a short memory.

            • by skids (119237)

              Well, had you RTFA, you'd have known that when that explanation was offered, it was just one of many, and given the information they had at the time, did not fully explain the anomaly, so this is news in that they found and processed new information and pretty much proved what was far from "determined" back when the articles you refer to were posted.

      • by Anonymous Coward on Friday December 07, 2012 @04:53AM (#42213469)

        ... wasn't this already determined, around a year ago?

        Well not positively determined, the new analysis of the data does a better job of confirming it. So yes, as usual the summary is horribly wrong- it's a better proof of an existing theory, not a new theory.

      • Definitely old news, at least a few months old. Nothing new to see here...

      • ... wasn't this already determined, around a year ago?

        It was covered on Slashdot [slashdot.org]. :-)

    • by wvmarle (1070040) on Friday December 07, 2012 @02:20AM (#42213005)

      The most impressive thing is that we can actually measure this minute effect to such an accuracy that we know there is something unexpected going on. And then subsequently accurately explain this inaccuracy.

      • by bostonsysadmin (2776707) on Friday December 07, 2012 @03:32AM (#42213207)
        Seriously... it is just so laughably insane. If you were to tell someone from even just the 1940s that we would have an object doing this and that we could measure its progress to an incredible degree of precision, they would laugh at you and think that you were insane. Seriously... how is there still religion in this world? JFC... wake up already.
        • Re: (Score:2, Flamebait)

          by wvmarle (1070040)

          Hey, this is support for religion, particularly the intellectual design theory!

          After all it must be some God or whatever that has designed the universe to such perfection that we can shoot stuff in space, and by the time it's out of our solar system can say "hey it's not where we expect it to be, it's a few meters off. Oh wait a moment, we forgot to account for some photons.".

        • Re: (Score:2, Funny)

          by Anonymous Coward

          Err, if JFC woke up already, I think we'd be pretty safe in keeping that religion going :-)

      • by klapaucjusz (1167407) on Friday December 07, 2012 @10:26AM (#42214701) Homepage

        The most impressive thing is that we can actually measure this minute effect

        According to Wikipedia [wikipedia.org], it's 8.74×10^10 m/s^2. If you integrate that over fourty years [wolframalpha.com], that's 17000 km, or 55 ms light-speed delay, which should not be too difficult to detect.

        --jch

        • by wvmarle (1070040) on Friday December 07, 2012 @11:30AM (#42215313)

          That is 55 ms on some 16 hours, seven orders of magnitude less. And it's not measured by round trip, but by Doppler effect.

          Then the calculations to where it is expected to be are so mighty accurate that we can actually know that this is an anomaly, and not within error. To be able to calculate where the craft should be, you must know very accurately the gravitational constant, the masses of the Sun and the respective planets, effects of the solar wind pushing the craft out (actually that's what they were trying to measure as well), the speed of the Earth relative to Voyager, and probably some relativistic effects. Probably I missed some variables that have to be taken into account here. That overall accuracy is simply mind boggling as there are so many variables involved that with the slightest error in some of them, you end up with a much larger error in the final result.

    • by Joce640k (829181) on Friday December 07, 2012 @03:00AM (#42213125) Homepage

      The article is way too long.

      No kidding...and written like one of those awful Dan Brown novels... ("we'll tell you in the next paragraph, honest!")

      • Nah (Score:5, Insightful)

        by SmallFurryCreature (593017) on Friday December 07, 2012 @04:21AM (#42213383) Journal

        Your attention span just... never mind, he wandered off.

        This is science kid, leave it for people who can read a full paragraph without needing a red bull. For once the article tells the complete story instead of being some butchered blog summary of a blog summary of a tweet of a snippet and the kiddies are up in arms because they actually have to use the reading skills they never mastered.

        • Re:Nah (Score:5, Insightful)

          by Joce640k (829181) on Friday December 07, 2012 @04:49AM (#42213459) Homepage

          This is science kid...

          Which is exactly why it shouldn't be written like a suspense novel.

          Quick summary for all the people who know the background, full story underneath for those who don't (or just like to re-read it...)

          • Re:Nah (Score:4, Insightful)

            by PPalmgren (1009823) on Friday December 07, 2012 @10:51AM (#42214883)

            I dunno, there's actually a benefit to this kind of approach. A public facing article, intended for the public, not just the 1% of us who love and understand science. I remember reading things like this as a kid and re-living the history of an event, feeling the experience of the scientist and their jubilation as they worked through a problem and found their answers. Science written in the form of a suspense novel brings people into the fray that would have otherwise ignored it. I'm all for it.

          • Re:Nah (Score:4, Insightful)

            by ceoyoyo (59147) on Friday December 07, 2012 @11:00AM (#42214973)

            It's an article in IEEE Spectrum. Spectrum is a magazine that covers things that might be interesting to electrical engineers. Often those things are background stories on papers published in IEEE journals.

            If you want the science, read the paper (or the abstract if you've got attention span problems). The Spectrum article was the right thing for a Slashdot summary to link to. Especially since it's a dupe of a previous Slashdot story that DID just cover the nitty gritty.

          • by chrismcb (983081)

            Quick summary for all the people who know the background, full story underneath for those who don't (or just like to re-read it...)

            But... this IS the full story. The story is about how they found the source.

        • Re:Nah (Score:5, Informative)

          by Anonymous Coward on Friday December 07, 2012 @04:58AM (#42213485)

          This is science kid, leave it for people who can read a full paragraph without needing a red bull.

          Err no. Science starts by giving you a brief summary of the theory and conclusions, then proceeds to get into the details. We call it an Abstract. This is a fluff piece which should have been titled "Thermal radiation theory confirmed as source of Pioneer slowdown". Most of the space is spent rambling on about the history of the mission and very little about the methods used to determine the results.

          • by necro81 (917438)

            This is science kid, leave it for people who can read a full paragraph without needing a red bull.

            Err no.... This is a fluff piece....

            IEEE Spectrum is not a science journal, per se, it is a (free) general interest publication from a professional organization. It's Popular Science, actually well researched and written, without unfounded hype about The Next Big Thing. Most importantly, it has with significant technical content (not dumbed down or spoon-fed) that's accessible to the curious, without first

          • Science starts by giving you a brief summary of the theory and conclusions, then proceeds to get into the details. We call it an Abstract.

            That's how a scientific paper is written. Scientific papers are not science, they are part of the output of science.

            Science is a process. This article describes the process that went into one scientific discovery. It includes details about that process, such as the story of how the data was preserved, that would not usually go into a scientific paper. What you call "ra

          • by chrismcb (983081)
            The article is titled "Finding the Source of the Pioneer Anomaly", and the article goes on to tell you how the found the source of the anomaly. This isn't about science and theory and conclusions. It was about detective work. Astounding that it reads like a detective novel. The whole point of the article was to ramble about the history.
        • This is Slash Dot you could post the Mona Lisa (La Gioconda) and someone would complain about the smile.... Hang on Hang on did I just refer to the Mona Lisa on a thread that's going a bit Dan Brown???

          That's it I need a holiday!!!!

        • This was a really bad article about science. (To be precise, it was a badly written article about one scientific investigation.)

          Do not confuse a deliberate abuse of writing techniques with the scientific inquiry that was its subject. Scientific findings should be presented with expository writing techniques, not with the techniques used in the detective and mystery genres.

          This piece could have been well written. It could have had an introduction, a body, and a conclusion. Its avoidance of these high level

    • by mosb1000 (710161) <mosb1000@mac.com> on Friday December 07, 2012 @03:04AM (#42213135)

      The article is about the importance of retaining your original scientific data, rather than saying "we've analyzed it and now we're done with it forever."

    • by Anonymous Coward on Friday December 07, 2012 @03:05AM (#42213139)

      about the same as the backward push your car experiences in reaction to the photons spit out by its high-beam headlights.

      Damn, I'm gonna start driving without my headlights on to get better gas mileage!

      • by JustOK (667959) on Friday December 07, 2012 @03:27AM (#42213189) Journal

        Keep them on and drive backwards.

      • Damn, I'm gonna start driving without my headlights on to get better gas mileage!

        And brake lights actually don't brake, but accelerate ...

      • by necro81 (917438)

        Damn, I'm gonna start driving without my headlights on to get better gas mileage

        Actually, driving without your headlights on would give you better gas mileage, but not because of the radiative pressure. The electrical power that goes into the headlights is generated, quite inefficiently, by the internal combustion engine. So turning off your headlights will reduce your engine's (mechanical) power demand by perhaps 100-200 watts. Then again, cruising down the highway at 100 kph requires many kilowatts o

        • 200W head lamps? Have you actually driven a car?
          • by necro81 (917438)

            200W head lamps? Have you actually driven a car?

            Yes, I've been driving for decades. I never said that the head lamps were 200 W electrical. The electrical rating nfor headlights is in the range of 50-75 W. However, I was careful to put my estimate in terms of mechanical power, because that's what the internal combustion engine produces. The alternator in a typical automobile, driven by the serpentine belt, creates the electrical power for the rest of the car, and it's a terribly inefficient process at

    • "There, you may resume."

      This conclusion was actually published months ago. But the article was still a good bit of history (and a lesson about data preservation).

    • by prefec2 (875483)

      Thanks. And wasn't this already reported half a year ago or so? Why is this news again? Who has such a short memory? I'm just wondering ...

    • by fermion (181285)
      IIRC, this was the conclusion from a year ago. Is the current article just rehashing old news, or is there some new development. I thought the thermal anisotropy was the established explanation?
    • by Briareos (21163) *

      It's thermal recall force from heat generated by components on Pioneer.

      Thermal recall? Are you sure it's not "total recoil" instead?

      np: Kettel & Secede - Canned Forever (When Can)

  • I hate IEEE Spectrum (Score:5, Informative)

    by TrekkieGod (627867) on Friday December 07, 2012 @01:51AM (#42212907) Homepage Journal

    I hate Spectrum. Not because they have bad articles, but because they never have anything that I haven't already been reading about for the past months, or even years.

    Hint to editors. If you ever get a submission with a link to Spectrum, chances are very high that Slashdot has covered [slashdot.org] it before [slashdot.org].

    • by tloh (451585) on Friday December 07, 2012 @03:05AM (#42213141)

      I too, stopped reading Spectrum a few years ago when real science article dropped to a trickle. However, this particular article is not bad. Not only was it authored by one of the original problem solvers, it was very readable despite the length. I was intrigued particularly by their description of how they modeled the craft. It struck me as they described having to contend with blueprints rather than CAD files and consulting retired engineers from the original mission, that they appeared to have forgotten there is a very nice physical model of the craft hanging from the ceiling of the Smithsonian:

      http://en.wikipedia.org/wiki/Pioneer_H [wikipedia.org]

      I'm sure given the stakes involved (the real likely hood of discovering exotic physics) they wouldn't have minded taking the "replica" down for examination.

      • I too, stopped reading Spectrum a few years ago when real science article dropped to a trickle. However, this particular article is not bad. Not only was it authored by one of the original problem solvers, it was very readable despite the length.

        Yeah, like I said, it's not that I had a problem with the quality of the article, it's just that it lacked new information. The summary didn't mention that this was about the heat pressure from Pioneer so, like a fool, I went on to read the whole article thinking that maybe this was something new, showing that the heat explanation wasn't enough, and there was actually new physics. Instead, the article contains absolutely no information I hadn't already read about over 6 months ago, and I was a bit bitter

    • by El Puerco Loco (31491) on Friday December 07, 2012 @03:32AM (#42213201)

      And if you're reading it on Slashdot, chances are that Slashdot has also covered it before.

  • Not so new (Score:5, Informative)

    by Dan East (318230) on Friday December 07, 2012 @02:00AM (#42212945) Homepage Journal

    Not so new of a theory, and already discussed here at Slashdot:

    http://science.slashdot.org/story/11/07/26/0135234/heat-most-likely-cause-of-pioneer-anomaly [slashdot.org]

    Everything from clouds of dark matter, weird gravitational effects, alien tampering and exotic new physics have all been blamed for the 'Pioneer Anomaly' — the tiny, inexplicable sun-ward acceleration acting on the veteran Pioneer deep space probes. However, evidence is mounting for a more mundane explanation. Yes, it's the emission of heat from the spacecrafts' onboard radioisotope thermoelectric generators (RTGs), slowly nudging the Pioneers off course, that looks like the most likely culprit. It's unlikely that this new finding will completely silence advocates of more exotic explanations, however.

    • by Anonymous Coward

      Even older: http://science.slashdot.org/story/11/03/31/1328258/Pioneer-Anomaly-Solved-By-1970s-Computer-Graphics

  • Low on gas!
  • I know it is unscientific of me, but I hate it when the answer is so much less interesting than the mystery. Not because I dislike seeing a mystery solved but because when the answer is mundane it just means we have to look else where for the really earth shaking discoveries. Hopefully some day in my life time we will make some truly earth shaking discovery. I remain optimistic.
    • Re: (Score:3, Insightful)

      by Anonymous Coward

      How was this not interesting? Less energy than is put out by your headlights on your car was actually slowing down a multi-tonne spacecraft zipping through space at over 36,000 miles per second! While its not groundbreaking, it definitely is interesting science, and its frigging SPACE man!

      Higgs Boson was discovered and proved to be real. They might even have found a previously undetected particle as well!

      Dark matter was proven to exist and the mystery of why the universe is expanding faster and faster was s

      • How was this not interesting?...

        ...What the heck do you want, Science to prove God Exists and invite him over for freaking tea?!?...

        ?

        Now that would be both interesting and difficult to accomplish for "Science", since it would involve scientists believing in something greater than themselves. It is much simpler and easier to proclaim, "God can't be proven! Pics or it doesn't exist!"

      • by 3dr (169908)

        "zipping through space at over 36,000 miles per second! "

        Correction: Pioneer spacecraft are travelling at about 10 miles per second. Which is 36,000 mph.

        Or in more popular mass-media units, about 633,600 football (US) field lengths per hour.

    • I know it is unscientific of me, but I hate it when the answer is so much less interesting than the mystery.

      I feel perhaps you're not looking at it the right way. So there's no brand new physics here. But it shows a number of really cool things.

      1 Science is not limited by human scales. Dispite being only within the solar system, the probe is at nuimaginable distances travelling at unimaginable speeds, yet they could still measure the effect of a force which is unimaginable tiny.

      2 It shows yet again that eve

    • by chrismcb (983081)
      What were you hoping for? Elves? Faires? Pixel dust?
      I find it fascinating that the heat from the electrical circuits is slowing this thing down. AND that they figured it out! Absolutely amazing.
  • by ChrisMaple (607946) on Friday December 07, 2012 @02:15AM (#42212985)
    If the tail lights hadn't burned out.
    • by Sulphur (1548251)

      If the tail lights hadn't burned out.

      If we can see your tail lights, then it is still under warranty.

  • by Anonymous Coward
    Damn, I always thought it was the Invisible Pink Unicorn just fucking with us. Now, science has me questioning my blind faith. Curse you science!!! ::shakes fist::
  • by blanchae (965013) on Friday December 07, 2012 @02:30AM (#42213045) Homepage
    The design of these spacecrafts is simply amazing. No wonder the US was the technological marvel of the world at the time. Considering the tools that were available then and the thought that was put into the effects of space on the motion, is mind boggling. Not to mention a power source that will last 88 years and the fact that they are still going and communicating while using a 1 bit camera to create fantastic pictures. I am humbled. The technology that was created and developed as a side effect of this monumental tasks is what made the US a technology giant. We need more of this positive vision and less of the negative sabre rattling.
    • It'll last longer than 88 years. The half life is 88 years... that means it's only halfway done after 88 years. All it's going to do is lose efficiency over the next thousand years or so.

    • by Maow (620678)

      The design of these spacecrafts is simply amazing. No wonder the US was the technological marvel of the world at the time. Considering the tools that were available then and the thought that was put into the effects of space on the motion, is mind boggling. Not to mention a power source that will last 88 years and the fact that they are still going and communicating while using a 1 bit camera to create fantastic pictures. I am humbled. The technology that was created and developed as a side effect of this monumental tasks is what made the US a technology giant. We need more of this positive vision and less of the negative sabre rattling.

      I agree with everything you've said, but... I think it's a 1-pixel camera, not 1-bit.

      TFA refers to images stitched together pixel-by-pixel, but the images appear to have natural, though low bit depth colour.

      • by skelly33 (891182)
        Actually...

        The man who wrote the software for the image processing to handle the raw data that came out of that "camera" works in the Computer Science department at the local community college here now. I have spoken to him at length on this topic. He clarified that it is not a camera at all, but simply a "light sensor" (think sensitive photoresistor). The only thing that makes it able to render an image at all is the rotation of the spacecraft. He also explained that the rotating motion coupled with the
        • by Maow (620678)

          Actually...

          The man who wrote the software for the image processing to handle the raw data that came out of that "camera" works in the Computer Science department at the local community college here now. I have spoken to him at length on this topic. He clarified that it is not a camera at all, but simply a "light sensor" (think sensitive photoresistor). The only thing that makes it able to render an image at all is the rotation of the spacecraft. He also explained that the rotating motion coupled with the linear direction of the craft resulted in really interesting and strange swooping distortions of the "image" produced which was why they needed him to write something special to correct the curvature of the images. All pretty fascinating stuff.

          Fascinating stuff indeed. I gather you're near Ottawa? I seem to recall from TFA that one of the authors was based there. (I'm in Vancouver myself.)

          Anyway, if the sensor is as you describe, I'm curious how they colourized it - was that done in post-processing or was the device able to determine the colour itself?

          I guess I'm still curious about the number of bits the device captured - seems to me a single bit would not be sufficient, but am willing to learn anything about how they accomplished it.

          • by skelly33 (891182)
            The color was derived from multiple passes using red and blue filters over the same photo sensor. Green was derived from red and blue and hence we get the RGB color representation. Some info describing that is on this page [blogspot.com] - not a primary source, but matches what I recall.

            Also, I don't believe we're talking about "bits" here at all - this was all analog technology. My college instructor is in the Monterey, CA area.
  • Summary (Score:5, Informative)

    by michaelmalak (91262) <michael@michaelmalak.com> on Friday December 07, 2012 @02:31AM (#42213047) Homepage
    They were able obtain a longer history of telemetry data by getting it from some guy's laptop hard and finding some mag tapes under a staircase, and they reverse engineered hard-copy blueprints with the help of retired TRW engineers into modern CAD & FEA, and determined that the RTGs were bouncing thermal energy off the dish, creating recoil -- about the same amount as a car's headlights throwing photons forwards push the car backwards.
  • Maybe in the future, the design of probes should be such that the emanation of energy creates a micro-sail. Maybe it won't matter given the heliosheath, but all other things being equal, I'd prefer its own forces to accelerate it, rather than hinder it.
  • According to roman_mir it's the unions' fault.

    • Ok, that made me chuckle.

      That said, there seems to be a bit of a downmodding campaign against him recently. I don't agree with his premeses, but given them his arguments are generally good. He's certainly no troll and it is a shame to see dissenting opinions simply downmodded. Hopefully whoever has it in for him wil run out of modpoints soon.

  • Don't want to get a double fine from the Vogons...

  • the truth is out there
  • by Dr. Hok (702268) on Friday December 07, 2012 @04:58AM (#42213487)
    When I click the link on my android phone, it redirects to the mobile site, from there back to the normal site, again to the mobile site and on and on, until my browser barfs out. Nice. Engineering at its best.
  • by blogagog (1223986) on Friday December 07, 2012 @05:14AM (#42213539)
    If you don't feel like reading the very long and mostly unrelated story, here is the gist: "The puzzling deceleration was produced by the asymmetric radiation of waste heat created onboard the spacecraft. Read more to find out why we believe this." Seems like an awfully long article just to relate that bit of info imo.
  • Here's something sad (Score:5, Interesting)

    by argStyopa (232550) on Friday December 07, 2012 @08:38AM (#42214197) Journal

    ....the entire mission cost -all the years in total - for Pioneer 10 was approximately $350 million (2001) USD. (It'll reach Aldebaran in about 2 million years.)

    That's a little bit under a single week of NASA's budget this year. ($19bill) ...or about 4 hours of the Defense budget ($677 bill) ...or about an hour of the Social Security+Medicare budgets ($1.92 trillion).

  • Was there not a /. article a half a year ago that blamed heat for the slowdown?

    Also worst summery ever, it needs to actually mention what this new theory is.

  • Not so much "NASA" in the whole but individual research groups which change and disband with time. Private individuals pretty experience the same with childhood photographs and videos.

    Some of the original moon landing video tapes were lost, recycled or decayed. For the 40th anniversary they digitally restored copies from the public. These "restored" ones were better than the originals from analog days. But there is always the nagging hint some future scientific discovery may compromised by lacking th
  • by peter303 (12292) on Friday December 07, 2012 @12:09PM (#42215905)
    Detailed modeling of the radiation leak hypothesis.
  • Quote: "Three decades after its discovery, we can now say there is no exotic cause for the Pioneer anomaly: The puzzling deceleration was produced by the asymmetric radiation of waste heat created onboard the spacecraft."

    My skimming skills are getting better the older I get. I want the answer, then if it's interesting I'll go for the details.

  • Those mountains of data are more like molehill's by today's standards.
    • by cusco (717999)
      No kidding. We have customers whose security cameras generate a terabyte of data in an hour at a single site. I used to Fed Ex 9-track tapes with 'enormous' 100 mb files on them, because there was no other reasonable way to transfer such a massive amount of data. I remember being excited when 16 mb flash drives hit the market for only $176, but my boss said, "Brian, for $176 you can cart around a wheelbarrow full of floppies."
  • Hi everyone,

    Contrary to what is being reported here, this story is not a dupe. This story, which I, for one, found very well written, recounts the whole saga of determining whether thermal recoil asymmetry could account for the Pioneer anomaly. It is based on the latest publication on the topic, which is dated June 2012 and is still behind a paywall at PRL.

    Basically, previous report on thermal recoil where interesting in theory but insufficiently conclusive, because they were consistent with a constant dece

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