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#51
June 24th 04, 11:41 AM
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It was greater than expected deceleration.
Perhaps it is Nemesis at 90 degrees but that would throw a curve in the trajectory.....so perhaps not. "Paul F. Dietz" wrote in message ... Abdul Ahad wrote: I was casually checking the weekly mission data archived he- http://voyager.jpl.nasa.gov/mission/...orts/index.htm when I noted the velocities of both probes (relative to the Sun) were edging lower by small amounts over the past 8 years: Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s Any ideas as to what's causing this slow down anyone? The sun's gravity, of course. Paul 
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#52
June 24th 04, 12:50 PM
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William A. Noyes wrote:
It was greater than expected deceleration. Perhaps it is Nemesis at 90 degrees but that would throw a curve in the trajectory.....so perhaps not. The figures to the accuracy given are not greater than the expected deceleration from gravity. There has been a very small extra deceleration noted, as discussed elsewhere in this thread. That is probably due to some mundane effect like radiation pressure. Paul
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#54
June 24th 04, 06:45 PM
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In article ,
Abdul Ahad wrote: These two Voyagers are probably more closely watched than the nearby explorers like Cassini, mars rovers, etc. They carry the hopes and dreams of all the peoples of this planet: firstworld, third world, black, white, religious, aitheists, rich, poor, arrogant, peaceful and the like... Humanity's first 'message in a bottle' is well on its way to some exotic world waiting with open arms on the opposite shores of a boundless cosmic ocean! pure hallucination... I was hoping they would keep the remote sensing cameras turned on with some miraculuous ability built into them to take long exposure photographs. Sure the fields and particles data about the termination shock and heliopause is invaluable scientific data but just imagine the kind of deep sky observations that could have been made from this distance with cameras! No more solar glares, no full moons, no Zodiacal light, no bright planets...just the eternal glow of the Milky Way all around! The unimagined views from a thousand dream locations... Abdul Ahad OTOH from the current distance of the Voyagers, the Sun still shines some 100 times brighter than the full moon does as seen from Earth.... -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://www.stjarnhimlen.se/ http://home.tiscali.se/pausch/
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#55
June 24th 04, 07:21 PM
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Louis Scheffer wrote:
Tim Auton tim.auton@uton.[groupSexWithoutTheY] writes: (Abdul Ahad) wrote: [snip] Search for "pioneer anomaly". It's very interesting, mainly because nobody seems to know what's causing it. This is just wishful thinking by the theorists, who want something new to explain. A careful look at Pioneer shows there are a number of features that cause it to radiate a bit more of its heat in the anti-sunward direction. This is just right to account for the observed slowdown. Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10, Phys.Rev. D67 (2003) 084021. http://arxiv.org/abs/gr-qc/0107092 I'm the author so my opinion may be somewhat biased, of course. A most interesting paper. Prompted me to re-read Anderson et. al.'s updated paper. I laughed when I read this bit "It was arbitrarily argued that there was an incorrect determination of the reflection/ absorption coefficients by a large factor." They're talking about you, dude!  Your argument about multi-layered insulation seems sensibleenough to me though. For other who may be interested, here's Anderson et. al.'s. paper which argues against some of the points Louis makes in his paper (this version pre-dates the latest version of Louis's paper, I don't know if has been updated): Search for a Standard Explanation of the Pioneer Anomaly Mod.Phys.Lett. A17 (2002) 875-886 http://arxiv.org/abs/gr-qc/0107022 I have a feeling I'll have to read the 200 or so references and do some calculations of my own before I can form a valid opinion on this. Either that or stick an exact replica of Voyager in a vacuum chamber and do some precise measurements. Tim -- My last .sig was rubbish too.
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#56
June 24th 04, 07:28 PM
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"Mike Hawk" wrote:
IIRC that article didn't dispute that Voyagers and Pioneers weren't slowing down due to gravity, but that their rate of deceleration was greater than expected. Here's part of the article http://tinyurl.com/2jpnz WELL? DUHHH???...something else is at work on these poor little intersteller MOFO's from Earth I'm a real scientist (I've got letters after my name). Actually, there are several forces at work on them apart from gravity. Gravity is the dominant effect though. The question is how large these forces are and whether they account for the unmodelled acceleration in Anderson et. al.'s original paper. In other words, the question is whether there is new physics out there or whether Anderson et. al.'s modeling of the forces leaves something to be desired. The latter is more likely, but nobody seems to have come up with a model that satisfies everyone and precisely matches the data yet. There are plenty of references in another branch of this thread if you're into reading scientific papers. In my experience though, people who start rebuttals with "WELL? DUHHH???" and list their references as "I seem to recall" aren't all that interested in acquainting themselves with the facts. Tim -- My last .sig was rubbish too.
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#57
June 24th 04, 07:40 PM
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Tim Auton wrote:
I'm a real scientist (I've got letters after my name). Whoo. There are plenty of references in another branch of this thread if you're into reading scientific papers. In my experience though, people who start rebuttals with "WELL? DUHHH???" and list their references as "I seem to recall" aren't all that interested in acquainting themselves with the facts. Yeah, well, welcome to Mick's World. He's vying with Mini-Min for most aliases. Brian Tung The Astronomy Corner at http://astro.isi.edu/ Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/ The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/ My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
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#58
June 24th 04, 09:18 PM
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"Paul Schlyter" wrote in message ... In article , Abdul Ahad wrote: These two Voyagers are probably more closely watched than the nearby explorers like Cassini, mars rovers, etc. They carry the hopes and dreams of all the peoples of this planet: firstworld, third world, black, white, religious, aitheists, rich, poor, arrogant, peaceful and the like... Humanity's first 'message in a bottle' is well on its way to some exotic world waiting with open arms on the opposite shores of a boundless cosmic ocean! pure hallucination... I was hoping they would keep the remote sensing cameras turned on with some miraculuous ability built into them to take long exposure photographs. Sure the fields and particles data about the termination shock and heliopause is invaluable scientific data but just imagine the kind of deep sky observations that could have been made from this distance with cameras! No more solar glares, no full moons, no Zodiacal light, no bright planets...just the eternal glow of the Milky Way all around! The unimagined views from a thousand dream locations... Abdul Ahad OTOH from the current distance of the Voyagers, the Sun still shines some 100 times brighter than the full moon does as seen from Earth.... But what a sight it would be
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#59
June 24th 04, 10:38 PM
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In message , Louis Scheffer
writes Louis Scheffer writes: Jonathan Silverlight writes: In message , Louis Scheffer writes Note that when they put Cassini into a gyro-only mode for the gravity wave searches, it experienced an anomalous acceleration about 3x that of Pioneer, due to non-isotropic waste heat radiation. This effect is difficult to model, and the pre-launch estimates were off by 50%. But the theorists then do a song and dance about how this can't apply to Pioneer, all engineering data to the contrary. Interesting! Do you have a reference for that? (I could search, of course) My reading of the solar conjunction relativity experiment was that they _didn't_ find an anomaly, because they had modelled the heat output correctly. I'm working from memory here, but my recollection is that they knew there was non-isotropic heat rejection, so they added a constant force for this and fit it using trajectory data. They got a good fit, but the value of the radiation forces was different than their pre-launch estimates. Found it! It's http://arxiv.org/abs/gr-qc/0308010 Note that the paper has been withdrawn, but thanks to the magic of arXiv the original version 1 is still available. I've got that one, and the Bertotti et al. paper that appeared in Nature (and doesn't mention the Pioneer effect at all. I've argued on various newsgroups that if there really was uncertainty in the thermal model they wouldn't have such nice low residuals) I know experiments were done at opposition to look for gravity waves, but have the results been published yet? And has the reason for withdrawing the Anderson et al. paper been made public?
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#60
June 25th 04, 03:38 AM
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Jonathan Silverlight wrote in message ...
In message , Louis Scheffer writes Louis Scheffer writes: Jonathan Silverlight writes: In message , Louis Scheffer writes Note that when they put Cassini into a gyro-only mode for the gravity wave searches, it experienced an anomalous acceleration about 3x that of Pioneer, due to non-isotropic waste heat radiation. [...] (and doesn't mention the Pioneer effect at all. I've argued on various newsgroups that if there really was uncertainty in the thermal model they wouldn't have such nice low residuals) The uncertainty is in the amount of the effect. Whatever amount this is, though, it should be constant. So once you fit the value, the residuals will be very small, as small as if the effect did not exist. Why should it be constant? Because the amount of radiated heat from the RTGs is constant, and because the spacecraft must keep its antenna pointed at Earth. Forces in other directions are averaged out by spin (for Pioneer) and by symmetry (for Cassini). In theory this should be resolvable as a force directed at the Earth (not the Sun) but this can't be deternined for Pioneer, since it's so far away, and for Cassini, since the experiment was done at opposition. Lou Scheffer
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