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The Pioneer Anomaly
remcook
post Aug 16 2005, 04:27 PM
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http://www.planetary.org/news/2005/pioneer_anomaly_faq.html

The planetary society may be checking it out...

QUOTE
The Planetary Society has committed to raise the funds to preserve the priceless Pioneer data from destruction.


After years of analysis, but without a final conclusion, NASA, astonishingly, gave up trying to solve the "Pioneer Anomaly" and provided no funds to analyze the data. The Pioneer data exists on a few hundred ancient 7- and 9-track magnetic tapes, which can only be read on "antique" outdated computers. The agency is going to scrap, literally demolish, the only computers able to access and process that data in the next few months!
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remcook
post Aug 16 2005, 04:40 PM
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Some background reading...

http://arxiv.org/find/astro-ph/1/ti:+pioneer/0/1/0/all/0/1
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tedstryk
post Aug 16 2005, 06:53 PM
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Won't New Horizons be spin stabilized when not in encounter mode?


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remcook
post Aug 16 2005, 07:43 PM
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Quote from alan stern:

QUOTE
Yes, we spin most of cruise, stopping only rarely. It costs fuel that we want to hoard for encounters and KBO DeltaV. And yes, our radio science team hopes to look for
the Pioneer anaomaly. Contact Len Tyler or Ivan Linscott at Stanford.


in the new horizons thread:
http://www.unmannedspaceflight.com/index.p...topic=675&st=20

so some more things to look forward to
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Guest_Richard Trigaux_*
post Aug 17 2005, 06:37 AM
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Could not the Pioneer tapes be saved on a more modern support, before scraping the computers which can read it? So far as we know there may be still valuable data to infer from them, especially with the affair of the "pioneer anomaly".

Much was already said about this anomaly:

-the gravitaion law working differently at great distance...
-effect of cosmological dark matter surrounding the sun...


or simpler:
-systematic mistakes somewhere into the measurement chain.


Perhaps the NASA and many scientists prefer the second set of explanations. But so long as the first set cannot be completely ruled out, the question remains open.
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Jeff7
post Aug 17 2005, 07:09 PM
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QUOTE (remcook @ Aug 16 2005, 11:40 AM)


I looked at some of those things, but still am not quite clear on what this anomoly is.
And what's up with saving this? I think I missed out on this stuff.

It looks like the Pioneers have long stopped transmitting, but the data hasn't been analyzed yet, and now NASA wants to destroy the computers that can read the tapes? Is that the gist of it?
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remcook
post Aug 17 2005, 08:09 PM
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QUOTE
It looks like the Pioneers have long stopped transmitting, but the data hasn't been analyzed yet, and now NASA wants to destroy the computers that can read the tapes? Is that the gist of it?


that's what I understand yes...

The anomaly is basically that the pioneer spacecraft (I think it was seen in Ulyssus and Cassini as well) accelerate slightly different than what one would expect from our understanding of gravity.
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deglr6328
post Aug 17 2005, 11:10 PM
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QUOTE (remcook @ Aug 17 2005, 08:09 PM)
that's what I understand yes...

The anomaly is basically that the pioneer spacecraft (I think it was seen in Ulyssus and Cassini as well) accelerate slightly different than what one would expect from our understanding of gravity.
*



Not Cassini but Galileo. Cassini is 3-axis stabilized (thrusters). Galileo was spin stabilized. The error introduced by the use of thrusters basically washes out any hope of seeing any other miniscule anomalous effects.
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Guest_Richard Trigaux_*
post Aug 18 2005, 06:59 AM
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As far as I understand from readings in the press, the Pioneer probes (ant others) would slow down slighty more than expected from only the Sun gravity. This led to some interesting but far reached speculations.

Some asked if the gravity law was not exactly 1/R2.

The most consistent speculation is that, like the galaxy shows an excess (sometimes ten times) of invisible mass, called dark matter, the solar system may have some too (although much less, a fraction of a %). From close to the Sun, we feel only the Sun's attraction, but further in space we feel the Sun's more the dark matter's attraction. This could be explained if the dark matter is made of low energy subatomic particles; many would orbit the galaxy, with speeds in the 200km/s range. Some would orbit the Sun with still smaller speeds in the km/s range.


But the measurement of the anomaly is based on many far-reached and difficult estimates, such as the toss of sun's light on the space probe, or gaz leak from the reservoirs. A slight error or false assumption, and the result would be very different. This is why the Pioneer anomaly did not upset the science community. A precise measurement of this anomaly would perhaps do.
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Bob Shaw
post Aug 18 2005, 08:24 AM
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QUOTE (deglr6328 @ Aug 18 2005, 12:10 AM)
Not Cassini but Galileo. Cassini is 3-axis stabilized (thrusters). Galileo was spin stabilized. The error introduced by the use of thrusters basically washes out any hope of seeing any other miniscule anomalous effects.
*



So presumably the New Horizons vehicle won't be stable enough, for long enough, either...


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Remember: Time Flies like the wind - but Fruit Flies like bananas!
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The Messenger
post Aug 26 2005, 09:08 PM
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QUOTE (Richard Trigaux @ Aug 17 2005, 11:59 PM)
As far as I understand from readings in the press, the Pioneer probes (ant others) would slow down slighty more than expected from only the Sun gravity. This led to some interesting but far reached speculations.

...
But the measurement of the anomaly is based on many far-reached and difficult estimates, such as the toss of sun's light on the space probe, or gaz leak from the reservoirs. A slight error or false assumption, and the result would be very different. This is why the Pioneer anomaly did not upset the science community.  A precise measurement of this anomaly would perhaps do.
*


Painstaking and careful analysis is a more exacting description.

http://arxiv.org/find/astro-ph/1/au:+Turys...S/0/1/0/all/0/1

http://arxiv.org/abs/gr-qc/0104064

http://arxiv.org/abs/gr-qc/9906112

Anderson, Nieto & Turyshev's paper- rebuttal - papers with the astrophysical community spans more than a decade now, and signatures of the anomalies have been found everywhere they have found the time and money to look for them.

The community should be giving this type of research highest priority -

Nowhere is it written in stone gravity behaves exactly as was predicted and observed a more than a century ago. If the observational data indicates otherwise, why are we so certain the status que is the status correct?
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antoniseb
post Aug 26 2005, 10:42 PM
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QUOTE (The Messenger @ Aug 26 2005, 04:08 PM)
The community should be giving this type of research highest priority


The highest priority? I think finding all substantial Earth Crossing asteroids would be more important. Basic exploration of the Solar System should be more important. Looking for extra-solar planets should be more important. Galactic census missions should be more important. Studies of Sgr A* and the things orbiting it should be more important. Studies of distant Type 1a Supernova should be more important. etc.

The ESA has considered launching a probe specifically to measure this effect with greater precision, but it didn't get funded.

Perhaps you could tell us how you would probe this phenomenon, and what the various outcomes would tell us? Then we can talk about priorities.
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The Messenger
post Aug 29 2005, 05:25 PM
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QUOTE (antoniseb @ Aug 26 2005, 03:42 PM)
The highest priority? I think finding all substantial Earth Crossing asteroids would be more important. Basic exploration of the Solar System should be more important. Looking for extra-solar planets should be more important. Galactic census missions should be more important. Studies of Sgr A* and the things orbiting it should be more important. Studies of distant Type 1a Supernova should be more important. etc.

The ESA has considered launching a probe specifically to measure this effect with greater precision, but it didn't get funded.

Perhaps you could tell us how you would probe this phenomenon, and what the various outcomes would tell us? Then we can talk about priorities.
*


Two things:

1) I would take the mother-and-hen approach suggested by Nieto. Pioneer 10 & 11 demonstrated the virtues of simple, spin stabilized, thermally balanced probes. I would add a lot of health monitoring gear, but otherwise the probes should be very simple. They should have transmitters capable of using both phase-locked loop and ultra-stable oscillator ranging frequency control, multiple bands.

There should be at least two different types of chicks - one designed with a great deal of solar drag, the second fairly streamlined. Placed into identical trajectories at the same time, this would allow differentiation of unknown forces from solar wind effects. Perhaps even better would be ‘umbrella chicks’ that could trade-off between solar sail and coast modes, thus keeping the clutch together.

The mother should hover close enough to calibrate and study emissivity and radiation, but distant enough not to disturb momentum.

2) If one assumes the Pioneer anomalies are real and not artifacts, there should be supportive evidence, and many fundamental implications.

The solar wind may not be the only force moving objects away from the center of the solar system. Anderson had to add a linear component to the solar wind to model the acceleration of Galileo and Ulysses: http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf p21:

QUOTE
The radio Doppler and ranging data can be fit to the noise level with a time-varying solar constant
in the fitting model [82]. We obtained values for the time-varying solar constant determined by Ulysses
FIG. 10: Galileo best fit Doppler and range residuals using CHASMP. navigational data during this south polar pass [81]. The inferred solar constant is about 40 percent larger at perihelion (1.3 AU) than at Jupiter (5.2 AU), a physical impossibility!

We sought an alternative explanation. Using physical parameters of the Ulysses spacecraft, we first converted the time-varying values of the solar constant to a positive (i.e., outward) radial spacecraft acceleration, ar, as a function of heliocentric radius.


(my bold)

Throw a spring constant into elliptical orbits, as Anderson did to model Ulysses, and all hell breaks loose. Fly-bys and orbits don’t return correct planetary masses, long distance navigation breaks down, and gravity anomalies crop up everywhere.

Such a force is consistent with known observational facts. Figuring out if it is real should be given highest priority.
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algorimancer
post Aug 29 2005, 05:40 PM
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It seems to me that a simple means of checking this notion would be to track long-period comets (many of them). No spacecraft required smile.gif
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The Messenger
post Aug 29 2005, 06:12 PM
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QUOTE (algorimancer @ Aug 29 2005, 10:40 AM)
It seems to me that a simple means of checking this notion would be to track long-period comets (many of them).  No spacecraft required smile.gif
*


Too wide of error bars - Comets are always outgassing, changing in mass, color, orientation. We are looking at accelerations of less than 60 ppm.

Also, Radar tracking has proven to be less accurate than physical modeling suggest, as we learned from the Mars Climate orbiter and Polar Lander...perhaps Anderson's unmodeled force is the culprit.
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