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Pioneer 10 and 11 anomylous acceleration

  1. May 28, 2008 #1
    I heard an interview with a physicist on the radio who was talking about how the pioneer 9 and 10 felt an anomylous acceleration towards the sun during their missions. The force was 1/10 millionth of a G and according to the physicist who helped try to solve this mystery at the JPL labs, the problem is still unsolved. I am curious if any of you have insights about this mystery and any theorized solutions.
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  3. May 28, 2008 #2


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  4. May 28, 2008 #3


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    The subject has also been discussed many times on these Forums, such as here:
    anomalous acceleration of Pioneer 10 and 11,
    The Pioneer Anomaly,
    Does the PA show that DM/DE is dynamically important in the outer solar system?.

    A recent 'Sky & Telescope' article: "Pioneer Anomaly" Solved?, note the question mark! It still is very much an open question.
    (Emphasis mine)

    You may be interested in a concise summary of the effect and some possible explanations from the "Does the PA show that DM/DE is dynamically important in the outer solar system?" thread here.

    Last edited: May 28, 2008
  5. May 28, 2008 #4
    Thanks Mapes, normally I try as hard as possible not to use Wikipedia, but they have a nice list of possibilities treating the anomaly.

    Thank you Garth, for the many nice references listed, I will digest them in due time. So Garth you believe it was due to uneven heat emission from the crafts, right?
  6. May 29, 2008 #5


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    Not exactly!

    What I have done in that last link (here) is to take Turyshev et al.'s paper
    The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation and add up all the possible 'normal physics' explanations for the effect and see what is left unexplained that might be caused by new physics.

    Uneven heat emission as a component of the normal physics explanation would be only part of the total anomaly.

    Note that what is actually measured is an unexpected blue shift in the signals coming from the spacecraft on top of the expected Doppler shift, this time acceleration is then most commonly interpreted as a anomalous sunwards acceleration.

    Several authors have commented that this unexplained residual (time acceleration or clock drift) is consistent with being equal to Hubble's constant and therefore may be cosmological in nature. However, it is not simply Hubble expansion showing up locally as it is in the wrong direction - an inwards acceleration not an outwards Hubble flow.

    The mystery continues.....

    Last edited: May 29, 2008
  7. May 31, 2008 #6
    Yes, you give a very nice treatment to the mystery Garth.

    Maybe there were little green men hitching a ride to the outher rim, unbeknownst to NASA :)
  8. Jun 23, 2008 #7
    Pioneer distance anomaly

    Hi, I was reading about the pioneer anomaly on Wikipedia.


    First of all, apologies. I know that this question isn't entirely appropriate to this thread but I haven't yet worked out how to post a new topic.

    It says that the spacecraft has an ‘unaccounted for’ acceleration of about 9 * E-10 m/s^2

    Then it says that over one year this equates to about 5000km

    I then used s=1/2 a t^2 to check this but I am getting a result that is a factor of about 10 out.

    t^2 = (365 * 24 * 60 * 60)^2
    t^2 = 9.94E14 seconds

    s=½ * a * t^2
    s= ½ * 9 * 9.94 * E4
    = approx 450km.

    Am I missing something?
  9. Jun 23, 2008 #8


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    You are referring to Wikipedia! I think you are correct.

    Welcome to these Forums Zman, you will find we treat Wikipedia articles with caution around here. :smile:

    Of course, the PA is not measuring an acceleration nor distance from the Sun, I will copy from a link I included erroneously above, but because the edit facility timed out I was unable to repair it!

    1. The PA is measured as a residual blue Doppler shift on signals returned back to Earth. The value of the frequency change or time acceleration is equal to:

    ad = (2.92 ± 0.44) × 10−18 s-1.

    2. This can be interpreted as an acceleration (either towards the Sun or the Earth) equal to
    aP = (8.74 ± 1.33) × 10−10 m/s2.

    3. The effect has been constant and equal for both spacecraft from 10AU - 90AU. (Pioneer 10 - Feb 2003) (Other effects swamped it when they were closer than than 10AU from the Sun.)

    4. It does not show up in the orbital dynamics of the outer planets. This alone indicates to me that it cannot be modelled by modification in the gravitational field of the Sun. See Iorio's eprint Can the Pioneer anomaly be of gravitational origin? - answer: negative.

    (However, as a caveat, remember the residuals in Uranus’ orbit that led to the discovery of Neptune? Once Neptune was discovered there was still a residual that led to a search for Planet X. Pluto was found and the search discontinued. However Pluto was not Planet X, it is 2 OOM too small, so a residual in Uranus’ orbital elements still appears to exist!)

    5. That 'normal physics' from On-Board Systematics, (source The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation Turyshev et al.), can so far explain a maximum of:

    i Radio Beam Reaction Forc arb = (1.10 ± 0.10) × 10−10 m/s2. .
    ii Anisotropic Heat Reflection aah = (−0.55 ± 0.55) × 10−10 m/s2. .
    iii Differential Change of the RTG’s Radiant Emissivity are = 0.85 × 10−10 m/s2. .
    iv Constant Electrical Heat Radiation as the Source: not viable.
    v Helium Expulsion from the RTGs ahe = (0.15 ± 0.16) × 10−10 m/s2. .
    vi Propulsive Mass Expulsion apme = ±0.56 × 10−10 m/s2.

    This makes a maximum total of an = (2.1 ± 0.8) × 10−10 m/s2 that can be caused by normal physics leaving at least a minimum anomalous acceleration of ax = (6.6 ± 2.1) × 10−10 m/s2 to be explained.

    This may be expressed as a minimum Doppler shift or clock drift of

    ad residual = (2.20 ± 0.70) × 10−18 s-1.

    6. Furthermore note that Hubble's constant in similar units (1/(Hubble Time) expressed in seconds) is equal to:

    H = (2.4 ± 0.2) × 10−18 s-1 (with h=0.73) and where I have given H ±10% error bars, which is consistent with that unexplained residual ad residual in the PA.

    The PA may therefore be cosmological and not local in nature and viable gravitational theories that predict such a clock drift should be given due consideration.

  10. Jun 23, 2008 #9
    Thanks Garth

    But I am still confused.

    I suppose my question should really have been;

    How do I work out how much closer the Pioneer spacecraft is to the sun as a result of the PA after one year?

    You quoted the acceleration as;
    aP = (8.74 ± 1.33) × 10−10 m/s2

    Is it just a question of applying the formula;

    Dist = 0.5 x aP x t^2

    where Dist is the distance closer to the sun as a result of the PA
    and t is the number of seconds in one year.

    I don't need the physical result, I would just like to know if I have the correct principle.
  11. Jun 23, 2008 #10


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    You have the correct principle if the PA is caused by an actual deceleration.

    That is the spacecraft would be closer than predicted under normal theory by this amount.

    If the PA is caused by a time split between ephemeris and atomic time (a non-orthodox, 'new physics' explanation) then the acceleration is as expected and the spacecraft is situated where predicted.

  12. Jul 16, 2008 #11
    Re: Pioneer distance anomaly

    You are missing nothing, ZMAN; you got it right, apparently Wikipedia got it wrong.
    Assuming the anamolous doppler data corresponds to a real deceleration, your 450 km. per year is correct, not the Wikipedia value.

    Good catch.
  13. Jul 16, 2008 #12


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    Re: Pioneer distance anomaly

    I would be alarmed if uneven heat loss from a spacecraft could push it 5000 km per year from its expected location! That's > 0.5km/h!!
  14. Jul 16, 2008 #13
    Re: Pioneer distance anomaly

    Good point....and that would be only the radial component toward the sun.

    However, I don't think you can figure the velocity that way since you are assuming constant velocity ...which it isn't since it is under acceleration... No? If I'm not mistaken its the anamolous acceleration that is constant.

    You could however, say the acceleration would have to have been greater by a factor of 10....
    Last edited: Jul 16, 2008
  15. Jul 17, 2008 #14


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    Re: Pioneer distance anomaly

    Good point. So the anomalous acceleration is 500km/year per year?
  16. Jul 17, 2008 #15

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    Re: Pioneer distance anomaly

    No. Along with the factor of 10 error, the wiki article also did some rough rounding. You are correcting for the factor of 10 error, but keeping the rough rounding and adding a factor of 2 error. Taking the wiki value of (8.74±1.33)×10−10 m/s2 as a given, the anomalous acceleration is (870±130) km/yr2. (1 yr2= 9.96×1014 s2).
  17. Jul 17, 2008 #16


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    Re: Pioneer distance anomaly

    Right. OK. I was more interested in the unit i.e. that is was /year/year.

    So, if the craft were transported out to deep space and stopped, it would begin moving off at a rate of ~870km/yr2.

    Oh I see. That's not really that fast. I made a big flub when I calced it as a constant velocity.

    But it's still pretty substantial for "uneven heat loss" isn't it?
  18. Jul 17, 2008 #17


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    Re: Pioneer distance anomaly

    Yes it is! :rolleyes:

    Did you not read my earlier post on this thread, here?

    From a list of possible sources of acceleration
    It is an OOM too small.

    Constant heat loss would make a negligible contribution.

    These estimations were published by Turyshev et al. The Study of the Pioneer Anomaly: New Data and Objectives for New Investigation.

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