
#1
May2808, 07:51 AM

P: 684

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.




#2
May2808, 08:27 AM

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PF Gold
P: 2,532

If you haven't seen it already, you'll probably be interested in Wikipedia's page on the subject.




#3
May2808, 09:35 AM

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PF Gold
P: 3,273

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. 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. Garth 



#4
May2808, 06:11 PM

P: 684

Pioneer 10 and 11 anomylous acceleration
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? 



#5
May2908, 02:09 AM

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PF Gold
P: 3,273

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..... Garth 



#6
May3108, 12:39 PM

P: 684

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 :) 



#7
Jun2308, 09:30 AM

P: 85

Hi, I was reading about the pioneer anomaly on Wikipedia.
http://en.wikipedia.org/wiki/Pioneer_anomaly 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 * E10 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? 



#8
Jun2308, 09:55 AM

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PF Gold
P: 3,273

Welcome to these Forums Zman, you will find we treat Wikipedia articles with caution around here. 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: a_{d} = (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 a_{P} = (8.74 ± 1.33) × 10^{−10} m/s^{2}. 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 OnBoard 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 a_{rb} = (1.10 ± 0.10) × 10^{−10} m/s^{2}. . ii Anisotropic Heat Reflection a_{ah} = (−0.55 ± 0.55) × 10^{−10} m/s^{2}. . iii Differential Change of the RTG’s Radiant Emissivity a_{re} = 0.85 × 10^{−10} m/s^{2}. . iv Constant Electrical Heat Radiation as the Source: not viable. v Helium Expulsion from the RTGs a_{he} = (0.15 ± 0.16) × 10^{−10} m/s^{2}. . vi Propulsive Mass Expulsion a_{pme} = ±0.56 × 10^{−10} m/s^{2}. This makes a maximum total of a_{n} = (2.1 ± 0.8) × 10^{−10} m/s^{2} that can be caused by normal physics leaving at least a minimum anomalous acceleration of a_{x} = (6.6 ± 2.1) × 10^{−10} m/s^{2} to be explained. This may be expressed as a minimum Doppler shift or clock drift of a_{d 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 a_{d 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. Garth 



#9
Jun2308, 11:01 AM

P: 85

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. 



#10
Jun2308, 11:40 AM

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PF Gold
P: 3,273

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 nonorthodox, 'new physics' explanation) then the acceleration is as expected and the spacecraft is situated where predicted. Garth 



#11
Jul1608, 07:17 PM

P: 534

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. 



#12
Jul1608, 09:05 PM

P: 15,325





#13
Jul1608, 10:30 PM

P: 534

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.... 



#15
Jul1708, 09:51 AM

Mentor
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#16
Jul1708, 10:00 AM

P: 15,325

So, if the craft were transported out to deep space and stopped, it would begin moving off at a rate of ~870km/yr^{2}. 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? 



#17
Jul1708, 10:18 AM

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PF Gold
P: 3,273

Did you not read my earlier post on this thread, here? From a list of possible sources of acceleration 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. Garth 


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