Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror
Space Science

Pioneer Anomaly Solved 147

Posted by samzenpus
from the space-anchor dept.
First time accepted submitter gstrickler writes "After years of work recovering and analyzing old mission data and vehicle schematics, a just published analysis(Pdf) provides strong evidence for anisotropic thermal radiation being the source of the slowing of the Pioneer 10 and 11 spacecraft. The theory isn't new, but the recovered data and new analysis provide solid evidence that at least 80% of the deceleration is accounted for by anisotropic thermal radiation. Members of The Planetary Society were instrumental in recovering the data and helping fund the analysis. The lesson is, in space, it matters what direction your heat radiating surfaces point."
This discussion has been archived. No new comments can be posted.

Pioneer Anomaly Solved

Comments Filter:
  • by jhoegl (638955) on Thursday April 19, 2012 @05:48PM (#39740143)
    Heat makes things go fast!
    • You mean slower? Cause that's what happened in this case.

      • Re:This just in (Score:4, Informative)

        by Fluffeh (1273756) on Thursday April 19, 2012 @06:04PM (#39740303)

        Faster, slower - just depends on where the heat is being emitted - either towards where the craft is going (mainly the case here) or back towards where it came from.

        • Re: (Score:2, Informative)

          Faster, slower - just depends on where the heat is being emitted - either towards where the craft is going (mainly the case here) or back towards where it came from.

          In space, speed is a meaningless attribute without a point of reference. As well, space is non-euclidean in nature -- you can travel in a straight line and wind up in the same place you started. It's better to speak in terms of vectors and delta...

          • Re:This just in (Score:4, Insightful)

            by Iniamyen (2440798) on Thursday April 19, 2012 @09:14PM (#39741807)
            The "speed" of the Pioneer craft is usually referenced to the Sun and it's orbit
            • Heliocentrism is just as wrong as Earth Centrism. There is no "center" all things are relative. The concept of "speed" is flawed.

              Consider the concept of two ships, heading in opposite directions each traveling at the "speed" of light (C), how fast are they going relative to each other? The flaw comes not from the "speed" but from the reference point at which one measures "speed"; you change the perspective you change the equation, and that changes everything.

        • And, I suppose if we want to talk to the craft, we're kind of screwed because they have to be pointing the antenna toward us, and thus will continue to slow throughout the remainder of the mission.

      • Re:This just in (Score:4, Interesting)

        by l0ungeb0y (442022) on Thursday April 19, 2012 @06:09PM (#39740355) Homepage Journal

        Well actually, if they'd anticipated this and pointed the heat dissipating surfaces to the rear, Pioneer would be going faster.
        What the article did not state was how long it would take for these forces to cease forward momentum -- or if that is an issue.

        • Re:This just in (Score:4, Insightful)

          by Wraithlyn (133796) on Thursday April 19, 2012 @06:29PM (#39740533)

          I'm thinking pointing your heat dissipating surfaces directly towards the sun might decrease the efficiency of said heat dissipation.

          (Obviously this becomes less of a concern the farther from the sun you are)

          • by SharpFang (651121)

            What about pointing them sideways, backwards in relation to your orbital movement direction? The probes don't fly straight away from the Sun, that would waste enormous amounts of fuel due to actively fighting the gravity. Instead, they move in an increasingly wide orbit, by increasing orbital speed they make the orbit longer.

        • Re:This just in (Score:5, Interesting)

          by Chris Burke (6130) on Thursday April 19, 2012 @06:30PM (#39740545) Homepage

          Well actually, if they'd anticipated this and pointed the heat dissipating surfaces to the rear, Pioneer would be going faster.

          I'm not sure they'd have done anything... the effect is so small, completely irrelevant for the main part of the missions, and they might have other reasons for orienting the craft a certain way -- maybe to maximize cooling. As a rule the side that emits the most photons would also be absorbing the most from the sun. I realize the situation could be more complicated than this; if it was simple the result would have been calculated a long time ago.

          What I'm wondering is how many people will remove this from their "these handful of unexplained results in not fully understood circumstances mean all of physics are wrong (and my pet theory is right)" lists?

          • Re:This just in (Score:5, Insightful)

            by X0563511 (793323) on Thursday April 19, 2012 @06:36PM (#39740603) Homepage Journal

            Could one compromise and put the radiators perpendicular to the direction of the sun (and travel?) eg, not on the front or back, but on the sides? Provided you did so equally, any force resulting in their radiation should cancel itself out.

          • Re:This just in (Score:5, Insightful)

            by Anonymous Coward on Thursday April 19, 2012 @07:24PM (#39741005)

            [...]and they might have other reasons for orienting the craft a certain way -- maybe to maximize cooling.

            One end of the spacecraft is a big-ass radio dish, and the orientation is determined by pointing that dish at the Earth so that we can communicate with it.

            • by Chris Burke (6130)

              That's what I was going to say at first but I wanted to lead into the cooling thing -- anticipating the follow-on that they craft could have been designed differently to both radiate heat and radio in the same direction. Somehow.

            • by jrumney (197329)
              Even better. The radio dish provides shade from the sun's rays for the cooling surface behind.
          • by ultranova (717540)

            What I'm wondering is how many people will remove this from their "these handful of unexplained results in not fully understood circumstances mean all of physics are wrong (and my pet theory is right)" lists?

            None. They'll just claim it's a worldwide conspiracy of physicists publishing only articles conforming to the official story to keep funding. And if that fails they'll ask for unfiltered instrument readings: if those aren't provided then the scientists are hiding something, and if they, the inevitable

            • by Chris Burke (6130)

              Ain't it the truth. :(

              Though on the other hand it's been nearly a decade since I've heard the solar neutrino problem brought up as an obvious reason why everything mainstream physics thinks is wrong and [kooky theory] is totally obvious if you aren't a member of the Scientific Clergy.

              I think a lot of them will just move on using whatever other "anomalies" they please and ignore the times where they said "this means I'm right!" and they turn out to be wrong. Classic selection bias.

        • by v1 (525388)

          The lesson is, in space, it matters what direction your heat radiating surfaces point

          Am I arrogant for saying "wasn't this obvious?" Isn't that newton's first law at work? This looks like a job for Captain Obvious.

          • Re:This just in (Score:5, Informative)

            by Chris Burke (6130) on Thursday April 19, 2012 @07:55PM (#39741251) Homepage

            Am I arrogant for saying "wasn't this obvious?"

            Not really as long as you realize that some things seem obvious once you know they're true... Or as long as you just mean "obvious possibility".

            It's not like they didn't know that if there was a favored direction for the emission of radiation that this would affect the velocity of an object. The concept of a photon drive existed for decades before the Voyagers were launched. It's just that it was though that whatever net force there was would be essentially zero. Assume a uniform, spherical Voyager craft...

            This has been a long-standing possible, and then probable, explanation for the anomaly. Seems to have taken quite a bit of effort to figure out what the actual value of the force would be with sufficient precision. I remember what seems like a long time ago an article posted to /. about someone calculating the effect of heat radiation using Phong shading, the 3D graphics technique, as an approximation and got pretty good agreement.

            Going all the way to a complete finite element analysis, using multiple methods to come up with the coefficients for the model, and getting a result that leaves only a noise-level signal is pretty impressive. And not what I'd call obvious.

            So despite maybe feeling like it, it's not exactly a case of research by the Maximegalon Institute of Slowly and Painfully Working Out the Surprisingly Obvious.

        • by jrumney (197329)

          What the article did not state was how long it would take for these forces to cease forward momentum -- or if that is an issue.

          I'm more worried about how long it will take before it plunges back to Earth. But on a more serious note, I think the energy source that is causing the heat will run out before either of those events happen, and if not, hopefully Earth will be in a different place in its orbit than it was when Pioneer was launched when it flies past on its way back.

          • Re:This just in (Score:4, Informative)

            by monkeyhybrid (1677192) on Friday April 20, 2012 @06:48AM (#39744357)

            I wouldn't worry about that seeing as its velocity is enough to escape our solar system [wikipedia.org] altogether. It's more likely to get closer to Aldebaran, a star currently 68 light years away, than our own Sun... given 2 million years or so that is.

            • Correct, and yet, this loss of speed has cost it about 250k mi in it's first 34 years. On a percentage basis, it's irrelevant, but over time it adds up. Here's an older article [space.com] on the anomaly

              The discrepancy caused by the anomaly amounts to about 248,500 miles (400,000 kilometers), or roughly the distance between Earth and the Moon. That's how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct. ...

              The drift showed that the Pioneers were being accelerated toward the Sun (or, rather, decelerated in their movement away from the Sun) by a tiny but inexplicable amount. The level of drift is equal to a gravitational effect 10 billion times weaker than the pull of Earth.

            • by smpoole7 (1467717)

              Not to mention the fact that the source of heat will long since have gone cold before it even gets 1 light year from Earth.

      • by jrumney (197329)

        You mean slower? Cause that's what happened in this case.

        If it keeps it up, eventually it will be going fast in the other direction.

  • Err... is it the slowing of the craft, or the accelerating? Because the analysis refers to the "acceleration" of the spacecraft.

    • Re:Slowing? (Score:4, Informative)

      by Overzeetop (214511) on Thursday April 19, 2012 @05:50PM (#39740161) Journal

      Acceleration can be positive or negative.

      • by Overzeetop (214511) on Thursday April 19, 2012 @05:52PM (#39740181) Journal

        Sorry to self-correct - acceleration is a vector, it has both magnitude and direction. By summing all of the acceleration vectors, you get a resultant which determines the rate of change of your velocity.

        • by FrootLoops (1817694) on Thursday April 19, 2012 @11:52PM (#39742587)

          Your post and its high moderation made me feel overeducated, so I wrote a poem in archaic style to reinforce the feeling.

                Today I chanced to Look Down from my Ivory Tower;
                      the Vision horrified me.
                I saw the Peasants Clamoring blindly
                      for the Simplest Certain Knowledge
                      of the Calculus and of Physicks.
                I saw the Depth of Divide betwixt us thus:
                      One Man's Hidden Knowledge is Offal to th' Other.

          P.S. To be fair, the stuff you mentioned is somewhere around the programming equivalent level of "objects can have properties".
          P.P.S. Also, note the pun on "offal"/"awful" in the last line. It's the only good line of the poem. It's true in at least 4 ways.
          P.P.P.S. Sorry for such a weird post. Maybe it'll amuse someone.

    • Re:Slowing? (Score:5, Informative)

      by gbjbaanb (229885) on Thursday April 19, 2012 @06:01PM (#39740265)

      its accelerating backwards... ie, it's effectively got its "engine" (ie the heat radiating surface) pointing in the direction its heading, and this is slowing it down. I guess its still got a lot of velocity, but this is being reduced by the lack of anything pushing it in the right direction.

      In other words, in space, your hot arse is a form of propulsion!

      • Re: (Score:3, Informative)

        by geekoid (135745)

        Usually my hot arse propels people away from ME~

        • by Wraithlyn (133796)

          I believe this was the cornerstone of Einstein's Theory of Relativity.

        • by X0563511 (793323)

          For every action there is an equal and opposite reaction.

          Your ass propels you with as much force as it propels others.

          • Your ass propels you with as much force as it propels others.

            But that's only force, and we all know F==m*a. So his ass must propel his mass, while the gas from his ass must propel the mass of the masses behind his ass.

          • by sjames (1099)

            Especially in a small enclosed space...

    • by Sinn3d (1594333)

      Depends from what direction you are looking at it...

  • by Banichi (1255242) on Thursday April 19, 2012 @06:03PM (#39740289)

    Does this discovery have a relationship (however distant or inefficient) to Nuclear Lightbulb or Nuclear Photonic propulsion? https://en.wikipedia.org/wiki/Nuclear_lightbulb [wikipedia.org]

  • So now they know why its slowing down, can they fix the problem?

    I think they should reconfigure the main deflector to emit a tachyon pulse. That usually works.

    • by zAPPzAPP (1207370)

      Shoot it with a laser from over here, heat up the other side too.

    • "The problem", is the difference between flying out if the solar system forever, and flying out of the solar system forever at a very slightly slower speed ...

  • by fahrbot-bot (874524) on Thursday April 19, 2012 @06:17PM (#39740423)

    The lesson is, in space, it matters what direction your heat radiating surfaces point.

    It matters in bed too.

  • by GreatBunzinni (642500) on Thursday April 19, 2012 @06:28PM (#39740519)

    A portuguese aeronautics engineering student from Instituto Superior Técnico [ist.utl.pt] already figured this out way back in 2009 in his masters thesis, available here [ist.utl.pt].

    • by geekoid (135745)

      and now they have confirmed it.

    • So, how does his evidence and analysis stack up against the current one? (Especially in light of how little data was available until recently.)

      I.E. lots of people have theorized the effect, some have made (relatively crude) calculations supporting this as a cause - but this is the first using the whole dataset.

    • by careysub (976506) on Thursday April 19, 2012 @07:05PM (#39740873)

      Not exactly.

      Numerous investigators have been strengthening the case for thermal radiation as the cause for nearly a decade. The work of Bertolami, Francisco, et al in Portugal in 2008-2009 accounted for 67% of the acceleration, a then-new high point in this reckoning. This was a notable result, but they didn't "figure it out" or "solve" it, they strengthened the case that was by then widely believed to be correct. For an account of the whole story up through 2010 see: http://arxiv.org/pdf/1001.3686v2.pdf [arxiv.org] .

      The new study raises the level of confirmation to 80%, using data that they newly recovered, and further shows that the remaining 20% is not statistically significant. It is this study that deserves to be regarded as having "solved" the problem: accounting essentially for the full anomalous acceleration, and leaving no residual anomaly.

    • by Jorgensen (313325)

      Yep. These guys are coming to the same conclusion. Too bad that the title in slashdot claims it to be "solved" - the new paper does not claim to have it solved - merely to have reached the same conclusion with (what appears to be) a higher confidence level.

      Don't be misled by the title in Slashdot... :-)

    • by Chris Burke (6130)

      A portuguese aeronautics engineering student from Instituto Superior Técnico already figured this out way back in 2009 in his masters thesis, available here.

      Ah, that was the Phong shading one! Only in 2009? Seemed like longer ago...

      At the time people were saying "Oh, why Phong shading? What's so perfect about that?" and, well, the answer is it isn't, it's an approximation. Not a bad one, either, but still. So's the finite element analysis these folk did. Just a much better one.

  • by countach (534280) on Thursday April 19, 2012 @06:34PM (#39740591)

    Will this effect be powerful enough to ever cause it to stop, turn around and come home? And when it does so, how much strife will it cause to Spock and Kirk?

    • It depends on the particular machine race the spacecraft runs into; If it's Beserkers, they aren't going to care about the cute bald chick. :)

      The Borg on the other hand; If they look like 7of9, they can assimilate me anytime.

      .

    • In the orginal article about it in the Planetary Report (from the Planetary Society) the answer was yes! The spacecraft with their little p$rno plaques meant for salacious alien entertainment will loop back to our solar system... I don't know if that conclusion is still operative.
  • But if heat radiation does not have mass then why should it effect it?
    Does it have mass?

    • by countach (534280)

      Alpha and Beta radiation has mass. They are particles.

    • by MiG82au (2594721)
      It has momentum. C'mon, this is high school physics.
    • Re:Mass?? (Score:5, Informative)

      by Chris Burke (6130) on Thursday April 19, 2012 @07:31PM (#39741069) Homepage

      Does it have mass?

      In a sense yes. Radiation and all other forms of energy have relativistic mass, as in the m in E=mc^2, as in things that have more energy (moving objects, high-energy states of atoms and molecules, systems in general) have more mass as it applies to inertia and gravity.

      Heat radiation as in (mostly infrared) photons don't have rest mass. That's the m0 in E = root(pc^2 + m0^2*c^4). So they don't have mass in the sense of matter as you usually think of it. But it turns out the way you usually think of mass is not equivalent to matter. Even though the usual way you think about it is that they are.

      Hope that clears things up. :)

      • I thought that E=mc^2 meant that E could me converted to M not that all it was both energy and mass at the same time.
        And that massless photons when shot in one direction actually push back in the other.

        • Re:Mass?? (Score:5, Informative)

          by Chris Burke (6130) on Thursday April 19, 2012 @08:43PM (#39741583) Homepage

          I thought that E=mc^2 meant that E could me converted to M not that all it was both energy and mass at the same time.

          So did I! But it's not a conversion, it's an equivalence! Energy and mass -- relativistic mass, the quantity that informs our notions of gravity, weight, and inertia -- are really, always, the same thing just in different units. If there's more energy in a system, then it weighs more on a scale. Water weighs less than two hydrogen and one oxygen because it's at a lower energy state. This of course includes the energy that is in the form of rest mass.

          Rest mass is a form of energy. It can be converted into other forms of energy at a rate equal to m0*c^2. Energy and relativistic mass are always related by the equation E=mc^2.

          • by c++0xFF (1758032)

            It gets even more obvious if you use Plank units, where c = 1. Then, this equation becomes just E = m.

            If the term "equivalence" bothers you, just think of it as a unit conversion.

        • by nedlohs (1335013)

          You thought wrong.

          When you heat something up it gets heavier.

          • That's why hot air balloons work, after all...
            • That's why hot air balloons work, after all...

              That's more of an increase in volume causing an increase in displacement. Along the same lines: just because a battleship floats on water doesn't mean it's particularly light.

            • by nedlohs (1335013)

              Yes, you thought that through well didn't you?

              Air has a density of 1.204kg/m^3 at 20C, so a baloon with 3000m^3 of air has 3612kg of air. When we heat that air to 120C the density drops to 0.898kg/m^3 so 2694kg.

              Now lets pretend the mass increase from heating magically applies to all the original air - 3612kg of it. Our temperature change is 100C == 100K. Heat capacity of air ranges from 1.005 to 1.013 over our temperature range. Since we're going for the overestimate lets say it's 1.013.

              1.013 kJ/kg*K * 3612

              • by nedlohs (1335013)

                A 3612kg-2694kg = 918kg mass decrease.

                I knew I'd screw something up. Still:

                0.000000004kg versus 918kg - which one will matter most?

    • by blueg3 (192743)

      Radiative heat is actually just photons.

      Photons have mass and carry momentum, but don't have rest mass.

  • Old News (Score:4, Informative)

    by hemo_jr (1122113) on Thursday April 19, 2012 @06:42PM (#39740665)
    Or rather a confirmation of some preliminary work done years agor (2008) http://www.planetary.org/blog/article/00001400/ [planetary.org]
    • That's exactly the point of this new article, it confirms the theory by accounting reducing the variance to below the "noise" level. Scientifically and statistically speaking, it's a solid confirmation.

  • It is very nice to see this analysis come to a clear conclusion. There are many reasons for physicists and those who feel constrained by the laws of physics to wish for violations of known laws that have significant effects in our corner of the galaxy. But time after time mundane explanations based on known laws turn out to be right. At some point more people are going to catch that we are not going to continuously overturn accepted science. Eventually the philosophers and sociologists of science might
  • by slashmydots (2189826) on Thursday April 19, 2012 @07:58PM (#39741279)
    If I understand ion thrusters correctly (that's a big if), a big tank of neutral atoms are bombarded by electrons to knock other electrons out of orbit around those atoms, creating positive particles, which are electrostatically accelerated out a big metal screen thing and the motion of them going the opposite way makes your spaceship go the correct way.
    I believe thermal radiation in this article's context means heat being turned into infrared light, that means photons going the opposite direction can have a noticeable impact on an existing spaceship in a real world text over a relatively short distance in space. I would think a gigantic atom nucleus has thousands of times more mass than a photon so ion thrusters would be pretty effective over time. Now of course the opposite "kick back" reaction is proportionate to the amount of energy you're putting into the ions and their speed is ohhhhh just a hair slower than a photon (lol) but at least we can say the theory should work in real space based on this experience.
    • by Roachie (2180772)
      Yea, I was wondering about this as well. What kind of specific impulse this would represent?
  • This means it wasn't Voldemort making a Horcrux out of the Pioneer Plaque!
  • A spacecraft dedicated to disproving this anomally should be slingshotted out of the solar system to test this once and for all and address the reamining 20%. It could be a cheap spin-stabilized craft with a pinger and a transmitter and carefully studied thermal characteristics.
  • It's sort of like we're measuring a solar sail effect to the point that there is such thing as a Cd value in space.

  • Oh, I suppose I'd better RTF-preprint now. Just for a change.

"It's ten o'clock... Do you know where your AI programs are?" -- Peter Oakley

Working...