IPB

Welcome Guest ( Log In | Register )

16 Pages V  « < 9 10 11 12 13 > »   
Reply to this topicStart new topic
The Pioneer Anomaly
ljk4-1
post Feb 1 2006, 04:02 AM
Post #151


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



From The Planetary Society update:

Our strategy for the upcoming analysis of the newly available data can be summed up as follows: First, studying the early mission data may help us unambiguously determine whether the acceleration points towards the Earth, the Sun, or some other direction. Second, we hope to find out how the anomaly begins or if it was present throughout the mission. Third, we hope to be able to determine how this anomalous acceleration changed over time. Fourth, we will compare data from the two Pioneers to see if we can discern any notable differences in their behavior. Lastly, we will use the MDRs to develop a better engineering model of the spacecraft, making use, for instance, of finite element analysis methods to understand its thermal behavior.

In March 2006, for the very last time the Earth will be in a favorable position to receive Pioneer 10's radio signal. It is possible that Pioneer 10 is still able to transmit, despite the age of its electronics, the extreme coldness of deep space, and the diminishing amount of electrical power on board. The possibility that the Deep Space Network will attempt to reacquire Pioneer 10's weak signal is currently being investigated, raising the hope, however faint, that we may yet have another data point to aid in our investigation of the Pioneers' enigmatic behavior.

The rest is here:

http://planetary.org/programs/projects/pio...ate_200601.html


--------------------
"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

Go to the top of the page
 
+Quote Post
Guest_Richard Trigaux_*
post Feb 1 2006, 08:27 AM
Post #152





Guests






QUOTE (ljk4-1 @ Feb 1 2006, 04:02 AM)
From The Planetary Society update:

Our strategy for the upcoming analysis of the newly available data ...

The rest is here:

http://planetary.org/programs/projects/pio...ate_200601.html
*


So this data was recovered and is now safe. Good move. Now serious work can begin.


smile.gif
Go to the top of the page
 
+Quote Post
The Messenger
post Feb 1 2006, 03:54 PM
Post #153


Member
***

Group: Members
Posts: 624
Joined: 10-August 05
Member No.: 460



QUOTE (Richard Trigaux @ Feb 1 2006, 01:27 AM)
So this data was recovered and is now safe. Good move. Now serious work can begin. 
smile.gif
*

It is an extremely difficult and tedious proposition. Each operation of a thruster must be accounted for, and every encounter with a third body - a moon, a planet, and a planetary system requires accurate mass and distance estimates.

It will be interesting to see if the Pioneer probe data pans out in the lower orbits like Cassini, Galileo, and Ulysses. Each of these probes experienced, (or rather, accelerations were measured), that exceed the 'Pioneer' effect by at least one magnitude, however, it is not possible to untangle the measured acceleration from the solar wind: It is in the same direction. (I think this measured anomally in Galileo and Ulysses is also in the opposite direction from the Pioneer probe acceleration - I don't have any numbers, other than a magnitude for Cassini.)

We will be lucky if we can hear from Pioneer in March, but if I remember correctly, the probe is no longer executing commands, so it may not be possible to enter the Doppler-repeater mode necessary for accurate distant measurements. (In this mode, the Pioneer probes echoed back an ultrastable signal sent from the Earth a harmonic frequency. If we are only listening to the Pioneer transmitter, there is not sufficent accuracy in the on-board timing to obtain accurate distance estimates.)
Go to the top of the page
 
+Quote Post
Guest_Richard Trigaux_*
post Feb 2 2006, 09:54 AM
Post #154





Guests






QUOTE (The Messenger @ Feb 1 2006, 03:54 PM)
We will be lucky if we can hear from Pioneer in March, but if I remember correctly, the probe is no longer executing commands,
*


Why the probe is no longer executing commands? if it is because the power it receives is too weak, it would be worth using a large radio transmitter, such as Arecibo. Obtaining a last point of Pioneer effect is worth some seconds of Arecibo I think
Go to the top of the page
 
+Quote Post
Guest_Richard Trigaux_*
post Feb 2 2006, 09:56 AM
Post #155





Guests






QUOTE (The Messenger @ Feb 1 2006, 03:54 PM)
It will be interesting to see if the Pioneer probe data pans out in the lower orbits like Cassini, Galileo, and Ulysses. Each of these probes experienced, (or rather, accelerations were measured), that exceed the 'Pioneer' effect by at least one magnitude, however, it is not possible to untangle the measured acceleration from the solar wind: It is in the same direction.  (I think this measured anomally in Galileo and Ulysses is also in the opposite direction from the Pioneer probe acceleration - I don't have any numbers, other than a magnitude for Cassini.)

*


It is not sure at all that the solar wind has a constant amplitude (speed, density, directio) everywhere. Especially it could be weaker out of the ecliptic,and eventually very variable. Ulysse data should tell us.
Go to the top of the page
 
+Quote Post
ugordan
post Feb 2 2006, 12:05 PM
Post #156


Senior Member
****

Group: Members
Posts: 3560
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (Richard Trigaux @ Feb 2 2006, 10:54 AM)
Why the probe is no longer executing commands? if it is because the power it receives is too weak, it would be worth using a large radio transmitter, such as Arecibo. Obtaining a last point of Pioneer effect is worth some seconds of Arecibo I think

It doesn't have to execute commands at all. All we need is detection of its carrier signal to measure the Doppler effect.

QUOTE (Richard Trigaux)
It is not sure at all that the solar wind has a constant amplitude (speed, density, directio) everywhere. Especially it could be weaker out of the ecliptic,and eventually very variable. Ulysse data should tell us.

It's a constant misconception/mixup that the solar wind is pushing on these probes. While to some extent you might say a force is being felt, a few particles per cubic cm hardly amount to much.
In reality, solar light pressure is the culprit in exerting quite measurable forces and torques on the spacecraft.
The same goes for a solar sail, it doesn't really ride on solar wind, but on light from the sun.


--------------------
Go to the top of the page
 
+Quote Post
The Messenger
post Feb 2 2006, 05:04 PM
Post #157


Member
***

Group: Members
Posts: 624
Joined: 10-August 05
Member No.: 460



QUOTE (ugordan @ Feb 2 2006, 05:05 AM)
It doesn't have to execute commands at all. All we need is detection of its carrier signal to measure the Doppler effect.

Measuring the carrier would give us the velocity, but not the distance, and the probes native carrier is much too unstable to gain an accurate reading of the velocity.

In the 'repeater' mode, the Pioneer probes would listen to a frequency from earth, then rebroadcast the same pattern at a frequency multiple. Since the ultrastable signal from Earth controls the oscillator, both timing elements are known with great precision.

QUOTE
It's a constant misconception/mixup that the solar wind is pushing on these probes. While to some extent you might say a force is being felt, a few particles per cubic cm hardly amount to much.
In reality, solar light pressure is the culprit in exerting quite measurable forces and torques on the spacecraft.
The same goes for a solar sail, it doesn't really ride on solar wind, but on light from the sun.
*

True, but the thermal effect is a little easier to model that the solar wind - for one thing, the particles in the solar wind may contain any charge, and this charge may either attract or repel the craft upon impact.

On both Ulysses and Galilio, Anderson & Co. had to use an unexpected solar vector to model the Solar wind effects, and a similar deviation was noticed in Cassini. The polarity of these vectors near Jupiter is opposite of what I stated earlier; that is, the apparent acceleration is towards the sun, just like Pioneer.

In any case, the PI's do not consider solar wind or heating effects to be primary candidates. A very comprehensive treatment of the problem can be found in:
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf

QUOTE (Anderson-etal)
Currently, we find no mechanism or theory that explains the anomalous acceleration. What we can say with some confidence is that the anomalous acceleration is a line of sight constant acceleration of the spacecraft toward the Sun.

Even though fits to the Pioneers appear to match the noise level of the data, in reality the fit levels are as much as 50 times above the fundamental
noise limit of the data.

Until more is known, we must admit that the most likely cause of this effect is an unknown systematic. (We ourselves are divided as to whether “gas leaks” or “heat” is this “most likely cause.”)

The arguments for “gas leaks” are: i) All spacecraft experience a gas leakage at some level. ii) There is enough gas available to cause the effect. iii) Gas leaks require not new physics. However, iv) it is unlikely that the two Pioneer spacecraft would have gas leaks at similar rates, over the entire data interval, especially then the valves have been used for so many maneuvers...  v) Most importantly, it would require that these gas leaks be precisely pointed towards the front of the spacecraft so as not to cause a large spin-rate changes. But vi) it could still be true anyway.

The main arguments for “heat” are: i) There is so much heat available that a small amount of the total could cause the effect. ii) In deep space the spacecraft will be in approximate thermal equilibrium. The heat should then be emitted at an approximately constant rate, deviating from a constant only because of the slow exponential decay of the Plutonium heat source. It is hard to resist the notion that this heat somehow must be the origin of the effect. However, iii) there is no solid explanation in hand as to how a specific heat mechanism could work. Further, iv) the decrease in the heat supply over time should have been seen by now.
...

Finally, we observe that if no convincing explanation is to be obtained, the possibility remains that the effect is real. It could even be related to cosmological quantities, as has been intimated...This possibility necessitates a cautionary note on phenomenology: At this point in time, with the limited results available, there is a phenomenological equivalence between the [standard] and [alternative] points of view. But somehow, the choice one makes affects one’s outlook and direction of attack. If one has to consider new physics one should be open to both points of view. In the unlikely event that there is new physics, one does not want to miss it because one had the wrong mind set.
Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 2 2006, 05:07 PM
Post #158


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?


--------------------
"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

Go to the top of the page
 
+Quote Post
Guest_Richard Trigaux_*
post Feb 2 2006, 06:49 PM
Post #159





Guests






QUOTE (ljk4-1 @ Feb 2 2006, 05:07 PM)
Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?
*


if it had an effect such as removing a part of the structure, it may change the thermal model in the way it receives thrust from solar light. But more likely many dust did not produced large break-up, but many pin-holes which change the thermal property, in a way similar for all the probes. (Or in a different way, as there may be seasons for interplanetary dust).
Go to the top of the page
 
+Quote Post
The Messenger
post Feb 2 2006, 07:04 PM
Post #160


Member
***

Group: Members
Posts: 624
Joined: 10-August 05
Member No.: 460



QUOTE (ljk4-1 @ Feb 2 2006, 10:07 AM)
Any chance there is a foreign object like a small meteoroid that impacted and stuck onto the Pioneer probes that may be affecting things?
*

Very unlikely. The two Pioneer probes are moving in nearly opposite directions, and we are talking about a constant acceleration towards the sun, not a one-time change in a velocity vector. So unless microparticle bombardment is both uniform and omni-directional, this can all-but be ruled out.

Another interesting observation: The Viking probes are losing power at a slower rate than nuclear theory predicts. Currently, the only explanation for this is an increase in the efficiency of the thermalcouples converting nuclear energy into electrical energy as the temperature decreases. (This is an expected improvement, but apparently the magnitude of improvement is greater-than-expected.)

Contact with Pioneer 10 should give us another data point concerning this thermal efficiency phenomenon. While unexpected quantum efficiency in an ultra-cold environment may be a factor, we cannot rule out the possibility that the nuclear decay efficiency and/or rate is an extremely weak function of the radiative and/or the gravimetric environment.
Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 8 2006, 03:26 PM
Post #161


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



Astrophysics, abstract
astro-ph/0602161

From: R. H. Sanders [view email]

Date: Tue, 7 Feb 2006 16:51:22 GMT (43kb)

Solar system constraints on multi-field theories of modified dynamics

Authors: R.H. Sanders

Comments: 10 pages, 5 figures, submitted MNRAS

Any viable theory of modified Newtonian dynamcs (MOND) as modified gravity is likely to require fields in addition to the usual tensor field of General Relativity. For such theories the MOND phenomenology emerges from an effective fifth force probably associated with a scalar field. Here I consider the constraints imposed upon such theories by solar system phenomenology, primarily by the absence of significant deviations from inverse square attraction in the inner solar system as well as detectable local preferred frame effects. The current examples of multi-field theories can be constructed to satisfy these constraints and such theories lead inevitably to an anomalous non inverse-square force in the outer solar system.

http://arxiv.org/abs/astro-ph/0602161


--------------------
"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

Go to the top of the page
 
+Quote Post
Guest_AlexBlackwell_*
post Feb 9 2006, 12:11 AM
Post #162





Guests






I'm surprised that you haven't mentioned this one yet, ljk4-1 tongue.gif

Planetary Radio had an interview with JPL's John Anderson on February 6, 2006:
Closing In On An Interplanetary Mystery: The Pioneer Anomaly.

Under a category similar to "DVD Extras": Emily Lakdawalla and Bruce Betts.
Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 9 2006, 12:13 AM
Post #163


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



QUOTE (AlexBlackwell @ Feb 8 2006, 07:11 PM)
I'm surprised that you haven't mentioned this one yet, ljk4-1  tongue.gif 

Planetary Radio had an interview with JPL's John Anderson on February 6, 2006:
Closing In On An Interplanetary Mystery: The Pioneer Anomaly.

Under a category similar to "DVD Extras": Emily Lakdawalla and Bruce Betts.
*


The signal was too weak for me to detect. cool.gif

Thanks for catching that one.


--------------------
"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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 9 2006, 04:19 PM
Post #164


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



General Relativity and Quantum Cosmology, abstract
gr-qc/0509021

From: Andreas Rathke [view email]

Date: Wed, 7 Sep 2005 12:45:40 GMT (259kb)

Pioneer anomaly: What can we learn from LISA?

Authors: Denis Defrere, Andreas Rathke

Comments: 19 pages, 4 figures. Talk given by D. Defrere at the conference "Lasers, Clocks, and Drag-Free", ZARM, Bremen, Germany, 30 May - 1 June 2005

The Doppler tracking data from two deep-space spacecraft, Pioneer 10 and 11, show an anomalous blueshift, which has been dubbed the "Pioneer anomaly". The effect is most commonly interpreted as a real deceleration of the spacecraft - an interpretation that faces serious challenges from planetary ephemerides. The Pioneer anomaly could as well indicate an unknown effect on the radio signal itself. Several authors have made suggestions how such a blueshift could be related to cosmology. We consider this interpretation of the Pioneer anomaly and study the impact of an anomalous blueshift on the Laser Interferometer Space Antenna (LISA), a planned joint ESA-NASA mission aiming at the detection of gravitational waves. The relative frequency shift (proportional to the light travel time) for the LISA arm length is estimated to 10E-16, which is much bigger than the expected amplitude of gravitational waves. The anomalous blueshift enters the LISA signal in two ways, as a small term folded with the gravitational wave signal, and as larger term at low frequencies. A detail analysis shows that both contributions remain undetectable and do not impair the gravitational-wave detection.

This suggests that the Pioneer anomaly will have to be tested in the outer Solar system regardless if the effect is caused by an anomalous blueshift or by a real force.

http://arxiv.org/abs/gr-qc/0509021


--------------------
"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

Go to the top of the page
 
+Quote Post
ljk4-1
post Feb 9 2006, 04:29 PM
Post #165


Senior Member
****

Group: Members
Posts: 2454
Joined: 8-July 05
From: NGC 5907
Member No.: 430



General Relativity and Quantum Cosmology, abstract
gr-qc/0602003

From: Antonio F. Ranada [view email]

Date: Wed, 1 Feb 2006 15:30:16 GMT (10kb)

A model for the Pioneer Anomaly

Authors: Antonio F. Ranada, Alfredo Tiemblo

Comments: 11 pages, no figures

We propose an explanation to the Pioneer Anomaly, the anomalous blueshift in the radio signals from the Pioneer 10/11 spacecrafts that remains unexplained 30 years after being discovered by a NASA team around 1975. It was detected as a Doppler shift that does not correspond to any known motion of the ships. In 1998, after many unsuccessful efforts to account for it, the discoverers suggested "the possibility that the origin of the anomalous signal is new physics".

We show here that the phenomenon has the same observational footprint as an acceleration of the atomic clocks time with respect to the astronomical time.

Surprisingly, this curious new idea turns out to be compatible with current physics; lacking a unified theory of quantum physics and gravitation, we cannot discard it a priori.

We expound a mechanism that produces such an acceleration as a result of the coupling of the background gravitation and the quantum vacuum. This suggests a solution to the riddle, in which the velocity of a receding ship, as deduced from the Doppler effect, is smaller than the value predicted by the standard theory of gravitation.

We conclude that the Pioneer Anomaly is probably the signature of the difference between the marches of the astronomical clock of the orbit and the atomic clock inside the ship.

http://arxiv.org/abs/gr-qc/0602003


--------------------
"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

Go to the top of the page
 
+Quote Post

16 Pages V  « < 9 10 11 12 13 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 31st August 2014 - 04:16 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.