Pioneer Anomaly Solved - Reflective Thermal Model

[bcrowell]

We've known for a while that the Pioneer anomaly couldn't be gravitational:
Iorio, "Does the Neptunian system of satellites challenge a gravitational origin for the Pioneer anomaly?," http://arxiv.org/abs/0912.2947

Now it looks like it's completely solved:
F. Francisco, O. Bertolami, P. J. S. Gil, J. Páramos, "Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft ," http://arxiv.org/abs/1103.5222

 

[Dale]

Very nice reference!

 

[JesseM]

A good nontechnical article on what was done in this paper:

http://www.technologyreview.com/blog/arxiv/26589/

 

[atyy]

After Pervect's post I checked to make sure the paper wasn't posted today.

 

[Drakkith]

Isn't it amazing that we can observe and calculate this to a precision so great that we had to take into account the reflection of heat from the main dish to account for the subtle deceleration?

 

[bcrowell]

Isn't it amazing that we can observe and calculate this to a precision so great that we had to take into account the reflection of heat from the main dish to account for the subtle deceleration?

Yes! To me, this is good motivation to do some fundamental tests of GR by sending up special-purpose probes as test masses. If they were specifically designed for the purpose (unlike Pioneer), we could get some amazing high-precision tests. The flyby anomaly is still unresolved, and although it's probably not real physics, if it is, it's a big deal.

 

[TrickyDicky]

I'm amazed at how easily convinced by a single paper just released that is based on a non-physical modelling (Phong shading) is people with apparently some scientific background, I mean, no further discussion, no "let's wait for some confirmation", nothing. The Pioneer anomaly is solved. Period.
Don't you feel a little bit of embarrassment?

 

[kmarinas86]

I'm amazed at how easily convinced by a single paper just released that is based on a non-physical modelling (Phong shading) is people with apparently some scientific background, I mean, no further discussion, no "let's wait for some confirmation", nothing. The Pioneer anomaly is solved. Period.

I know, right?

V. CONCLUSION AND OUTLOOK

In this study we have established a new method to model reflections of the Pioneer spacecraft thermal radiation with an increased accuracy, while maintaining the desired simplicity and computational speed of the approach previously proposed [13]. This new tool allows for a successful modeling of the most important features of the Pioneer spacecraft concerning thermal effects and its impact on the resulting acceleration.

The developed method, based on Phong shading, provides results that generally confirm those previously obtained in Refs. [13, 14]: the acceleration arising from thermal radiation effects has a similar order of magnitude to the constant anomalous acceleration reported in Ref. [2]. We believe that the chosen approach is most adequate for the study of this particular problem, taking into account all its specific characteristics. Moreover, this Phong shading method is well suited for future studies of radiation momentum transfer in other spacecraft .

The main difficulty in dealing with this problem has always been the lack of sufficient and reliable information for a detailed engineering modeling of the spacecraft , which justified a large number of reasonable hypotheses. We have achieved to overcome this caveat through a parametric analysis that takes into account a wide range of different scenarios. This strategy allows us to present a range of probable values for the thermal effects, which appears to be compatible with the signature of the Pioneer anomalous acceleration.

With the results presented here it becomes increasingly apparent that, unless new data arises, the puzzle of the anomalous acceleration of the Pioneer probes can finally be put to rest.

We have to keep in mind that reflection of light will not cause an acceleration towards the sun, but away from it. The best you could do with Phong shading is to reduce acceleration away from the sun to zero. It's not enough to just have the correct order magnitude.

Here's the conclusion of the other paper:

3 DISCUSSION AND CONCLUSIONS

We have investigated the impact that an anomalous, constant and uniform acceleration directed towards the Sun having the same magnitude of the PA would have on the
orbital dynamics of the Neptunian satellites Triton, Nereid and Proteus which move in the deep PA region of the solar system. Long data sets covering a large number of orbital
revolutions are currently available for them.

We, first, used an analytical approach which only considered the direct PA-type perturbations on the three satellites taken separately to work out the corresponding shifts in the radial, transverse and out-of-plane orbit components. In fact, also the indirect effects caused by the PA-affected mutual gravitational interactions among them should be, in principle, considered. Then, we numerically integrated the equations of motion with and without an extra-PA acceleration confirming the analytical findings. It turned out that only secular and sinusoidal signatures are present in the three orbit components; we showed that this is not in contrast with the absence of a secular effect on the semimajor axis. No quadratic terms appear in the transverse component, as, instead, it would happen if $$a$$ was affected by secular signatures.

Our analysis showed that the resulting anomalous orbital effects are much larger than the realistic orbit accuracies evaluated from a recent analysis of all the available astrometric observations by one-two orders of magnitude. However, it must be stressed that our investigation should be considered preliminary. Indeed, it would be necessary to refit the entire set of observations to the corresponding predictions computed by taking the anomalous PA effect into account. As an alternative approach, it would also be possible to fit the predicted observations without the PA to a set of simulated observations produced by including the PA. Our study demonstrates that such further investigations, which are beyond the scopes of this paper, should be considered worth the needed effort.

Also notice the premise of this paper:

If the Pioneer Anomaly (PA) was a genuine dynamical effect of gravitational origin, it should also affect the orbital motions of the solar system’s bodies moving in the space regions in which the PA manifested itself in its presently known form, i.e. as a constant and uniform acceleration approximately directed towards the Sun with a non-zero magnitude APio = (8.74 ± 1.33) × 10−10 m s−2 after 20 au from the Sun.

This is a flawed premise because if the Pioneer Anomaly were attributed to high gravitational potential regimes only, then you would not expect the Pioneer Anomaly to exist when in close range to a planet, such as Neptune, where the gravitational potential is low. Thus, it wouldn't be any surprise, if the Pioneer Anomaly were something occurring only at high gravitational potential, that it would not be observed for the moons of Neptune.

 

[bcrowell]

I'm amazed at how easily convinced by a single paper just released that is based on a non-physical modelling (Phong shading) is people with apparently some scientific background, I mean, no further discussion, no "let's wait for some confirmation", nothing. The Pioneer anomaly is solved. Period.
Don't you feel a little bit of embarrassment?

I'm not just convinced by this paper. I'm convinced by the accumulation of evidence. Turyshev and Anderson at JPL, the original discoverers of the anomaly, have been gradually increasing their estimates of the heat effect. Over the years, it became clear that the systematic uncertainties had been underestimated originally, and were really about the same size as the anomaly. It's also been established for a while now that the effect couldn't be gravitational (see the reference to the Iorio paper in my OP).

I don't think the overwrought and personal tone of your post is helpful.

 

[Redbelly98]

We have to keep in mind that reflection of light will not cause an acceleration towards the sun, but away from it.

But it's not reflection of sunlight. It is reflection of heat radiation from the pioneer, reflecting off the dish antenna away from the sun, causing an acceleration towards the sun.

 

[bcrowell]

This is a flawed premise because if the Pioneer Anomaly were attributed to high gravitational potential regimes only, then you would not expect the Pioneer Anomaly to exist when in close range to a planet, such as Neptune, where the gravitational potential is low. Thus, it wouldn't be any surprise, if the Pioneer Anomaly were something occurring only at high gravitational potential, that it would not be observed for the moons of Neptune.

Iorio is only assuming the equivalence principle plus, I suppose, additivity of fields (which is an incredibly good approximation in the weak field limit). If the equivalence principle fails, then the entire structure of general relativity falls apart. I'm not saying that's impossible, but it would be an extraordinary claim, and extraordinary claims require extraordinary evidence -- which we don't have here.

Although the paper I referenced only deals with the Neptunian moons, I believe a similar analysis has also been carried out for the outer planets themselves, and your objection wouldn't apply there.

You refer to a hypothesis that an anomaly occurs only when the gravitational potential is high, which would violate the weak-field additivity of fields. Can you refer us to a scientific paper that develops a theory that works this way, and that is consistent with all the observational evidence? It seems unlikely to me that you can, since a dependence on the gravitational potential is inconsistent with the basic structure of GR. GR only allows us to define a gravitational potential in static spacetimes, not in a general spacetime. Your proposal also doesn't make sense because even in spacetimes for which the gravitational potential can be defined, it's only defined up to an additive constant.

 

[TrickyDicky]

I'm not just convinced by this paper. I'm convinced by the accumulation of evidence. Turyshev and Anderson at JPL, the original discoverers of the anomaly, have been gradually increasing their estimates of the heat effect. Over the years, it became clear that the systematic uncertainties had been underestimated originally, and were really about the same size as the anomaly.

What accumulation of evidence? estimates are evidence?

It's also been established for a while now that the effect couldn't be gravitational (see the reference to the Iorio paper in my OP).

Even if this was true it doesn't follow logically that the anomaly is done with just because one paper says so, no matter how biased you are by previous estimates.
Or would you still maintain that the PA is completely solved?

I don't think the overwrought and personal tone of your post is helpful.

That is a pretty subjective assessment, are you sure you are not projecting?

 

[Redbelly98]

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Don't you feel a little bit of embarrassment?

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That is a pretty subjective assessment, are you sure you are not projecting?

Seriously, TD, let's keep the personal stuff out of the discussion. Expressing doubts about the Pioneer Anomaly is fine.

 

[Tanelorn]

Has the flow of very occasional high velocity gas atoms unbound by the gravitation field of the solar system been discounted? That was my first thought. I believe that the galaxy is full of matter of all sizes going very fast in all directions..

 

[Drakkith]

I'm amazed at how easily convinced by a single paper just released that is based on a non-physical modelling (Phong shading) is people with apparently some scientific background, I mean, no further discussion, no "let's wait for some confirmation", nothing. The Pioneer anomaly is solved. Period.
Don't you feel a little bit of embarrassment?

Embarrassment about what? Reading a new paper that shows a model which takes into account factors that hadn't been considered before? And I don't remember anyone absolutely claiming that this was the end all be all of the possibilities of the anomolies. Just an interesting paper. Not embarrassed in the least.

Has the flow of very occasional high velocity gas atoms unbound by the gravitation field of the solar system been discounted? That was my first thought. I believe that the galaxy is full of matter of all sizes going very fast in all directions..

Where are they coming from? Everywhere, or only certain directions? I'd guess that yes, that had been considered before, and if not, it is probably because it isn't a likely possibility.

 

[OnlyMe]

I'm not just convinced by this paper. I'm convinced by the accumulation of evidence. Turyshev and Anderson at JPL, the original discoverers of the anomaly, have been gradually increasing their estimates of the heat effect. Over the years, it became clear that the systematic uncertainties had been underestimated originally, and were really about the same size as the anomaly. It's also been established for a while now that the effect couldn't be gravitational (see the reference to the Iorio paper in my OP).

I don't think the overwrought and personal tone of your post is helpful.

While this is all interesting, gradually increasing estimates of the effects of heat loss until the results match observations, is not proof. It does present the possibility of testing the estimates at some point. Unfortunately, it will most likely be some time before funding for a properly designed test, involving the design, construction and launching, of a satellite will be available.

I hope that one estimated solution, will not end the search for a final solution.

 

[Drakkith]

While this is all interesting, gradually increasing estimates of the effects of heat loss until the results match observations, is not proof. It does present the possibility of testing the estimates at some point. Unfortunately, it will most likely be some time before funding for a properly designed test, involving the design, construction and launching, of a satellite will be available.

I hope that one estimated solution, will not end the search for a final solution.

I'm assuming that they didn't just increase their estimates for no reason.

 

[OnlyMe]

I'm assuming that they didn't just increase their estimates for no reason.

I did not say they were wrong, still they are estimates. Theoretical estimates need to be supported by experience in some form, before they can be accepted as more than guesses.

Mathematical and computer models are only as good as the information they begin with.

 

[TrickyDicky]

Reading a new paper that shows a model which takes into account factors that hadn't been considered before? And I don't remember anyone absolutely claiming that this was the end all be all of the possibilities of the anomolies. Just an interesting paper. Not embarrassed in the least.

You did not claim it, so I wasn't referring to you, someone else made that type of claim. Anyway I guess RedBelly is right, that term was uncalled for. Please do not pay attention to it.

 

[Tanelorn]

Drakkith, did you know that a star moving at 0.5% of the speed of light relative to us passed to within about 3 light years of Earth relatively recently? It is now about 7 light years away. My point being there is a lot of matter of all sizes flying around out there in the galaxy, and there is probably a net flow in one direction, possibly in the direction of the rotation of the galaxy, which might also be different to the net movement of our solar system.

 

[bcrowell]

Drakkith, did you know that a star moving at 0.5% of the speed of light relative to us passed to within about 3 light years of Earth relatively recently?

Really? That would be amazing. I think a typical relative velocity for stars in our galaxy passing by one another is about 100 km/s (Barnard's star's is about 140 km/s), which is about a thousand times smaller than that. Do you have more info on this?

It is now about 7 light years away.

This doesn't make sense to me. Barnard's star is 6 l.y. from us, is moving a thousand times more slowly than that, and is the record holder for proper motion.

My point being there is a lot of matter of all sizes flying around out there in the galaxy, and there is probably a net flow in one direction, possibly in the direction of the rotation of the galaxy, which might also be different to the net movement of our solar system.

The JPL folks have been working on this for decades. I can't imagine that they'd be so incompetent as to have never even estimated such an effect.

 

[Tanelorn]

Ben, was on the way home when I posted that in haste, this is the star I was thinking of, it moves in retrograde to the most of the rest of the galaxy:

http://en.wikipedia.org/wiki/Kapteyn's_star

My numbers are wrong, I mixed them up with hypervelocity stars near the center of the galaxy, but the idea itself might still be worth considering. I don't know what JPL have considered or the level of contribution assumed. Would they not have to make a best guess for this?

 

[Redbelly98]

http://en.wikipedia.org/wiki/Kapteyn's_star

That's too weak an effect. Kapteyn's star's effect on acceleration can be calculated using Google (← click link) and Newton's universal gravitation law. At 3*10^-15m/s², it is several orders of magnitude weaker than the Pioneer Anomaly of 9*10^-10m/s²

 

[GrayGhost]

Now, how's about solving the galactic rotation problem :)

 

[Tanelorn]

Redbelly, I didnt mean this star in particular, but instead any matter from the size of hydrogen atoms up which might be moving at a different velocity relative to the solar system. Nothing more than the wind into the spacecraft sail one atom at a time.

 

[Redbelly98]

Okay, understood.

 

[DaveC426913]

While this is all interesting, gradually increasing estimates of the effects of heat loss until the results match observations, is not proof. It does present the possibility of testing the estimates at some point. Unfortunately, it will most likely be some time before funding for a properly designed test, involving the design, construction and launching, of a satellite will be available.

I hope that one estimated solution, will not end the search for a final solution.

Let's keep this in perspective. We don't need to look for ghosts here.

Heat loss has always been by far the srongest candidate, but when we (the royal we) went to do the calculations as accurately as possible, we weren't quite satsified with the results, because, well, we like to be bang on.

It was only then, when the mystery was almost solved, but for a few split hairs, that people started looking for wilder, far less likely causes, such as a flaw in our understanding of gravity.

Now, that we have given the heat loss issue the attentionos it needs to cross our i's and dot our t's, do we see it works out the way it should have.

We always knew there was no mysterious force; there was always an understood solutionl we're just refining it. To try to launch dedicated satellites to hunt for ghosts would be folly.

 

[kmarinas86]

We always knew there was no mysterious force; there was always an understood solutionl we're just refining it. To try to launch dedicated satellites to hunt for ghosts would be folly.

It appears that, for some people, economic prudence trumps empiricism.

 

[DaveC426913]

It appears that, for some people, economic prudence trumps empiricism.

And some people prefer ghosts to the real-world. They'll keep claiming Area 51 alien autopsies and 9/11 conspiracies, claiming 'well there's no proof they don't exist'.

 

[kmarinas86]

And some people prefer ghosts to the real-world. They'll keep claiming Area 51 alien autopsies and 9/11 conspiracies, claiming 'well there's no proof they don't exist'.

You responded as if a gravitational anomaly that doesn't fit current theories would be paranormal.

 

[DaveC426913]

You responded as if a gravitational anomaly that doesn't fit current theories would be paranormal.

anomaly = unexplained by our current understanding of science

Wanting to reform our understanding of gravity is analagous to wanting to find the green guys in their saucers. It's be cool, but there's no real reason to go looking for something outrageous until we've exhausted all current theories that explain the facts. We found the explanation right where we knew it would be. We always knew heat radiation was the answer, we just needed to refine the model.

 

[kmarinas86]

right where we knew it would be.

Your use of the word "knew" is disturbing to say the least. A word such as "hypothesized" would be more appropriate in science.

 

[DaveC426913]

Your use of the word "knew" is disturbing to say the least. A word such as "hypothesized" would be more appropriate in science.

We need to hypothesize about radiative heat loss on spacecraft ? We've been dealing with that stuff for decades on planetary probes, satellites and high-powered space-born telescopes.

 

[kmarinas86]

We need to hypothesize about radiative heat loss on spacecraft ? We've been dealing with that stuff for decades on planetary probes, satellites and high-powered space-born telescopes.

When I spoke of needing a hypothesis, I wasn't referring merely to the existence of radiative heat loss. Of course we know radiative heat loss results in an additional component to thrust and that it exists on spacecraft , but we try to determine its consequences, so measures should be taken to start with a testable hypothesis, and not just assume what the result would be. You don't just assume that it fills in the gaps, but you try to see if it makes it less likely that other physics may be involved. In my opinion, that's what the recent studies did. It does not make it 0% likely, or even "much" less likely, just less likely.

 

[Drakkith]

While arguing the meaning of words is nice, the fact is that it was always much more likely to be radiative heat loss instead of some gravitational anomoly. We already knew about the heat loss, and had very good reasons to believe it was the culprit all along, but we just didn't factor in everything accurately enough.