On Wednesday, April 26, 2017 at 3:15:29 AM UTC+10, Craig Markwardt wrote:
On Monday, April 24, 2017 at 7:17:03 AM UTC-4, wrote:
On Thursday, April 20, 2017 at 7:36:10 AM UTC+10, Craig Markwardt wrote:
On Wednesday, April 19, 2017 at 5:50:36 AM UTC-4, wrote:
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Fig.2 from this link
https://arxiv.org/pdf/1204.2507v1
apparently suggests that the Pioneer anomaly may only be the
result of mismodelling of the solar thermal contribution.

Your interpretation of this paper is incorrect. This paper
(Turyshev et al 2002) demonstrates that most if not all of the
"anomalous" acceleration can be attributed to *internal* thermal
emission, generated by the RTGs and internal electronics.

I note no response.

Your comments were noted, but you were referring to the wrong
paper.

This is the exact wording from the 2012 version linked above:
Third, Fig. 2 is strongly suggestive that the previously reported
"onset" of the Pioneer anomaly may in fact be a simple result of
mismodeling of the solar thermal contribution; this question may
be resolved with further analysis of early trajectory data.

But such an error can't reside in the mismodelling of the solar
reflection/absorption characteristics of the HGA dish because
that was accurately determined prior to launch,

Just a side note, but thermal coatings do degrade over time, due
to exposure to solar UV as well as ionizing radiation (white
coatings become darker). So one can't be so certain about these
properties. That was one of the aspects covered by the thermal
analysis reported in Turyshev et al's 2012 paper.

You apparently agree that the RTG surface coating becomes darker
over time due to both solar radiation and radiation from within
the RTG's. But if in the unlikely event where RTG radiation
increases reflectivity, solar radiation would do likewise.

From RTG based darkening alone, all RTG surfaces will fade at the
same almost linear rate. The consequent solar radiation pressure
shortfall will deviate from the normally expected pressure and
reduce at that same rate as well. The pressure gradient will
follow the RTG line, **not the solar radiation pressure curve.**

http://members.optusnet.com.au/mskeon/solrtg.jpg

But surface darkening attributable to solar radiation will alter
exponentially. Theory may predict that this darkening will
significantly add to the inward acceleration closer to the sun
and taper off in a manner which compares with the Pioneer
anomaly over increasing distance, but that's not the case at all.
The darker sun facing surface will now radiate more of the RTG
internal thermal energy than the back face, overwhelming the
absorption capability of the solar radiation, thus driving the
spacecraft outward.

Don't tell me it won't.

Another problem is that absorbed solar thermal energy will also
radiate more readily from the darkened face. That applies to the
HGA dish as well.

The fix is to claim increased reflectability over time.
Probability: 1/1000000

It's obvious that either Turyshev or Anderson made a fairly
significant error. But it's strange that Anderson is deemed
wrong when a significant number of others also demonstrated the
existence of the anomaly, including yourself (2002)? Why should
this new result override all others when the average result from
all contributors well and truly favors the anomaly's existence?
That's a funny way to do physics.

What would be funny is to ALWAYS assume that the "average" of some
papers is relevant. ...

I note no response.

But actually it's not true to say no one else was considering
thermal. ...

I note no response.

Most folk can understand that the thermal solution doesn't work.

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You act as though analysts from the 1970's were using a set of
physical laws that analysts of today are not familiar with. But
that's not the case at all. Even if modifications have been made
to some of the physical laws the analysts of today would still
know exactly how the first data points showing the onset of the
anomaly were derived.

This is unsubstantiated. I am an analyst today of the Pioneer
doppler data, and I do not have enough information from that one
"onset" chart to understand how it was derived.

But a discrepancy between observation and what was expected
according to the prevailing physics at the time was clearly
noted, and it continued to increase until the spacecraft reached
the 20 AU mark. It didn't start out big. The anomaly was reported
by responsible physicist you know. They weren't just hand waving
to attract attention.

Furthermore, let's be clear what was happening in the early
1970s. The Pioneer spacecraft were the first spacecraft to be
sent to the outer solar system, with long cruise phases. Earlier
spacecraft were kept inside the Earth-Moon system, or directed to
the inner solar system. This new direction required new
attention to detail and modeling of the physical effects of the
space environment. No, the physical laws did not change, but the
modeling capability within the software that was used did not
capture all of the physics with the same fidelity.

Effects such as spacecraft spin and new relativistic physics were
being incorporated at that time. You can read the paper of Wong
& Lubeley from 1974 (AIAA Paper No. 74-845) which demonstrates
how the orbit determination groups were incorporating new
software with better capabilities.

Effects such as spacecraft propellant valve leaks were harder to
understand, and navigation analysts had to make do. What
physical laws does one apply to a valve that is leaky???

Before encountering Jupiter, both Pioneer spacecraft performed
frequent maneuvers (every few weeks), which disturbed the orbit
determination process, and also introduced more possibilities for
leaks.

Within the first 20 AU, the solar system radiation pressure is
significant. In fact, before Jupiter approach, the radiation
pressure is dominant over most of the force terms and is many
times the "anomalous" acceleration. You pointed out thermal
coatings, but let us not forget that the exact geometry of the
spacecraft has an effect. Is the antenna treated as parabolic
or flat-plate?

What about the cut-outs and antenna feeds, how are those
treated? These are not simple "physical law" issues. They have
to do with how accurately the spacecraft systems can be modeled.
Early in the mission, with computing power limited, some short
cuts were inevitably taken.

Each component would need to be analyzed properly, with a fairly
in depth description of the processes involved if the analysis
was expected to be taken seriously.

Which raises some questions here.
What data was plugged into the 2012 Turyshev computer simulation?
Were the RTG emissions and solar radiation pressures correctly
represented? Or were they in fact mismodeled as was the
assumption regarding Anderson's work?

Does the simulation software contribute toward the outcome? If
so, what was the programmer's information source? Was the
programmer or the source biased in any way? How could anyone
know any of this?

In the end it comes down to unconditional belief.

I would also like to point out that the planetary positions,
which we know so accurately today, were not known as accurately
at the time. In fact, the Pioneer and Voyager encounters were
used to refine the positions of the planets based on the fly-by
data. But, before the fly-by, the knowledge of the planet
positions ... and the corresponding acceleartions ... were less
well known. Thus, there is some uncertainty there too.

So, please do not pretend that the state of affairs in the early
1970s can really be compared to the state today.

The figure which you have referred to which shows the "onset" of
the acceleration, you have replotted. What you failed to show
was the uncertainty range (error bars) of the points. If you had
displayed those as well, you would have seen that the bars are
very large and that early data is not necessarily as stringent as
you say.

... The analysts weren't stupid back then, they noticed
this error and reported it. They couldn't explain it and neither
could anyone else. Your suggestion that the analyst were too busy
trying to navigate the spacecraft to properly analyze the
evidence is absurd. They weren't exactly alone in the world were
they!

Please let me clear. The Pioneer navigators were brilliant for
their time. I referred you to one paper. There are several, and
it is evident that they were highly skilled at their craft.
BUT... they were also not able to fully exploit the capability of
the radiometric data they were using. This was evident in their
own records which show they were upgrading the software steadily
with new capabilities. That early data MAY NOT have been as
accurate as desired.

I also want to say that I am in no way criticizing John Anderson
or his team of co-authors. His science track record is quite
excellent, and it is clear that they are very capable as well.
BUT AGAIN... the question is how good does someone have to be.
And the Turyshev paper demonstrated that a higher quality thermal
analysis can resolve the Pioneer "anomaly."

...
According to you, "when the spacecraft reached about 20 AU, the
search for unmodelled accelerations could begin in more earnest,
and more attention to detail was made". Why do you think a more
precise analysis of the more distant data points will be of any
use? It becomes quickly apparent where the curve is heading. But
so what? The horse has already bolted.

First of all, the quote is actually what Anderson et al. said in
their paper, not me. And second of all, what is your point?
If the goal is to accurately measure the "onset" of the anomaly,
then the early data which would or could have shown that is
largely lost forever. If the goal is to get an accurate measure
of the anomaly in late days (20 AU) then the Anderson et al 2002
paper is just fine... but it doesn't prove or disprove any of
your claims then. Anderson's paper claims the acceleration is
consistent with being constant, quite the opposite of your claim!

But he does acknowledge that there was an observed onset of the
anomaly which indicated a deviation from well known standard
physics at the time.

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The Turyshev team have perhaps managed to squeeze out a positive
result within the error bars, but they certainly haven't managed
to remove the problem. They could only shift it down a little at
best.

You can believe what you wish, but the Turyshev result shows that
the thermal and doppler solutions are consistent - within the
tolerances (see their Figure 4).

"believe" is the key word here isn't it.

I don't see you providing an alternate analysis of the thermal or
doppler data. And, other researchers working independently have
found similar results (see Bertolami's work that I pointed out
earlier). Turyshev et al's work demonstrates within the evidence
and known tolerances that the Pioneer "anomaly" has largely been
resolved.

That's better, but "has been largely resolved" is still a
gigantic overstatement. There's only a slight chance that the
anomaly no longer exists because it can only barely squeeze
between the questionable error margins. But at least nobody is
claiming absolute proof any more.

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Max Keon