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The Pioneer Anomaly
Guest_Richard Trigaux_*
post Jun 7 2006, 08:27 PM
Post #196





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Speed of the light??

What is the speed of the light in an ionized medium like the solar wind? Certainly a bit slower than c. Was this effect accounted for? And if so, was the model accounting with eventual de-ionization of the solar wind? or other anisotropy, like magnetic field keeping part of the wind into the ecliptic plane?
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ljk4-1
post Jun 9 2006, 08:06 PM
Post #197


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Astrophysics, abstract
astro-ph/0606197

From: Mauro Sereno [view email]

Date: Thu, 8 Jun 2006 15:28:39 GMT (49kb)

Dark matter vs. modifications of the gravitational inverse-square law. Results from planetary motion in the solar system

Authors: M. Sereno (Univ. Zuerich), Ph. Jetzer (Univ. Zuerich)

Comments: 7 pages, 4 figures, accepted for publication in MNRAS

Dark matter or modifications of the Newtonian inverse-square law in the solar-system are studied with accurate planetary astrometric data. From extra-perihelion precession and possible changes in the third Kepler's law, we get an upper limit on the local dark matter density, rho_{DM} < 3*10^{-16} kg/m^3 at the 2-sigma confidence level. Variations in the 1/r^2 behavior are considered in the form of either a possible Yukawa-like interaction or a modification of gravity of MOND type. Up to scales of 10^{11} m, scale-dependent deviations in the gravitational acceleration are really small. We examined the MOND interpolating function mu in the regime of strong gravity. Gradually varying mu suggested by fits of rotation curves are excluded, whereas the standard form mu(x)= x/(1+x^2)^{1/2} is still compatible with data. In combination with constraints from galactic rotation curves and theoretical considerations on the external field effect, the absence of any significant deviation from inverse square attraction in the solar system makes the range of acceptable interpolating functions significantly narrow. Future radio ranging observations of outer planets with an accuracy of few tenths of a meter could either give positive evidence of dark matter or disprove modifications of gravity.

http://arxiv.org/abs/astro-ph/0606197


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Guest_Richard Trigaux_*
post Jun 10 2006, 07:49 AM
Post #198





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Very interesting work.

Now just remains to compare the pioneer effect to the above results. If the Pioneer effect is larger, its origin must be searched into trite explanations (solar wind interaction and the like). The only interesting explanation would be about an unexpected behaviour of the solar wind.
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ljk4-1
post Aug 15 2006, 09:45 PM
Post #199


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I wonder if the recently announced one quadrillion members of the outer
Sol system play any role in the Pioneer Anomaly?


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"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Sep 2 2006, 08:11 PM
Post #200


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Test of the Pioneer anomaly with the Voyager 2 radio-ranging distance measurements to Uranus and Neptune

http://arxiv.org/abs/gr-qc/0608127


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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NMRguy
post Mar 27 2007, 09:34 AM
Post #201


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After a long hiatus, the Pioneer Anomaly finally resurfaces in the news circuit with an article from Space.com.

"Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources—known as radioisotope thermal generators (RTGs)—could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.

Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL. "

http://space.com/scienceastronomy/070327_s...ioneeranom.html
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Littlebit
post Mar 27 2007, 03:26 PM
Post #202


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QUOTE (NMRguy @ Mar 27 2007, 03:34 AM) *
"Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources—known as radioisotope thermal generators (RTGs)—could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.

Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL. "

I can see a problem right off the top with this scenario: The thermal output from the RTGs diminished considerably during the ten-plus years that the probes were monitored - but the measured acceleration anomaly during the same period was constant. (In order for the two effects to be related, you would have to explain why the depleting RTGs would result in constant acceleration.)
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tedstryk
post Mar 27 2007, 03:37 PM
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Most of the power loss is due to the degradation of the electronics - the actual decline in the output of the plutonium is much less pronounced.


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NMRguy
post Mar 28 2007, 09:57 PM
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The problem with the most recent space.com article is that it really lacked details, and their “preliminary results” had huge error bars. I’m going to wait for more concrete conclusions to come out in publication.

In the mean time, a very nice account of the progress and data recovery just showed up at the Planetary Society. (Thanks, Emily!) It’s a very nice read on the challenges of handling and eventually analyzing data generated over very long time periods. When the “experiment” started, computer technology was still very young.

Slava Turyshev gives a few details on the thermal modeling, but stops short of the claims in the space.com article.

"Our thermal modeling of the Pioneer vehicles is progressing very well. We finished the development of the geometric mathematical models of the spacecraft that include geometry and properties of most of the important spacecraft components and surfaces. We are now working on the thermo-dynamical model of the vehicles. At this stage, we have a very good understanding of heat re-distribution within the craft and soon will be ready to compute the heat flow to the outside of the craft. Soon, we will be able to tell whether or not heat contributes to the formation of the anomaly."

http://planetary.org/programs/projects/pio...e_20070328.html
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elakdawalla
post Mar 28 2007, 10:00 PM
Post #205


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You're welcome, but Slava wrote it; all I did was post it. I'll be happy to forward your thanks on to him. smile.gif

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nprev
post Mar 29 2007, 04:12 AM
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Not to drift into tin-hat-land at all, but I keep wondering if our imperfect understanding of the true value of the gravitational constant might be the ultimate culprit here. Experimental results for G are inevitably wildly different from one another even at the third digit past the decimal point, which implies uniquely large uncertainty for a physical constant (insert various curses for the fact that the Earth is not a uniform sphere of homogeneous composition here! smile.gif ) Can't understand why the particularly large error bars for this constant might not encompass the domain of the anomaly.

Try G=6.671281904 exp -11. If it works, I'll explain why via private correspondence in order to ensure that UMSF does not stray outside forum guidelines during the discussion (a distasteful possibility given the crackpot aura around gravitation); if not, forget I said anything, and thanks for the reality check. That's a firm heuristic, period.


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Comga
post Apr 4 2007, 04:18 AM
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QUOTE (tedstryk @ Mar 27 2007, 08:37 AM) *
Most of the power loss is due to the degradation of the electronics - the actual decline in the output of the plutonium is much less pronounced.

The half-life of the Pu 238 is 87 years. Since 1977 their thermal output has dropped ~21%.

Some of the reduction in electrical power generation is also due to the changing temperature differential, which decreases the efficiency of the thermal energy. Perhaps this is what you meant by "degradation of the electronics". However, this does not play into the net thrust of the thermal radiation.
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Comga
post Apr 4 2007, 04:21 AM
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QUOTE (nprev @ Mar 28 2007, 09:12 PM) *
Not to drift into tin-hat-land at all, but I keep wondering if our imperfect understanding of the true value of the gravitational constant might be the ultimate culprit here.....

IIRC, while our knowledge of the value of G is imperfect, our knowledge of the gravitational constant of the sun is very precise. So our value for G could be in error on the low side, but then our measure of the mass of the Sun would be in error on the high side, or vice versa.
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edstrick
post Apr 4 2007, 07:42 AM
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Radiation damage to the thermoelectric diodes causes a large fraction of the total power decline in RTG's. It's minor for a normal mission, but nukes your power margins (don't pardon the pun), on a decades long mission.
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lyford
post Jun 27 2007, 05:19 AM
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Exotic cause of 'Pioneer anomaly' in doubt
08:00 22 June 2007
NewScientist.com news service
David Shig

QUOTE
The 'Pioneer anomaly' – the mystifying observation that NASA's two Pioneer spacecraft have drifted far off their expected paths – cannot be explained by tinkering with the law of gravity, a new study concludes.

....

Now, Kjell Tangen, a physicist at the firm DNV in Hovik, Norway, says tweaking the law of gravity in a variety of ways cannot explain the anomaly – while also getting the orbits of the outer planets right. After modifying gravity in ways that would match the Pioneer anomaly, he inevitably got wrong answers for the motion of Uranus and Pluto.


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"Zis is not nuts, zis is super-nuts!" Mathematician Richard Courant on viewing an Orion test
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