Il giorno venerdì 5 maggio 2017 10:07:49 UTC+2, ha scritto:
Il giorno lunedì 1 maggio 2017 22:52:52 UTC+2, Craig Markwardt ha scritto:
Opening note...
Don't tell me it won't.

Hey bud, this is an open discussion forum. Whatever you think I should or should not say is completely irrelevant.


On Monday, May 1, 2017 at 8:25:16 AM UTC-4, wrote:
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.

Nope, you are incorrect. The 2012 paper concludes that "thermal recoil" is the explanation for the Pioneer anomaly. But not *solar* thermal. Or rather, the *new* thing of that paper is that by including the *internal* thermal effects (RTGs and electrical compartment dissipation) the anomaly is resolved. Previous work *ALWAYS* considered solar thermal recoil forces, and could not explain the anomaly. Again, the new thing in the Turyshev et al 2012 paper was inclusion of internally-generated thermal terms, and this is what "tipped the balance."


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. ... The pressure gradient will
follow the RTG line, **not the solar radiation pressure curve.** ...

Your writing appears to be motivated by intuition, but that is not the case. You can find a more correct and physics- and engineering-motivated discussion in books like "Spacecraft Thermal Control Handbook." Also, there are quite a few reference books on the degradation of thermal coatings from the time in the public domain.

Almost all known thermal coatings degrade w.r.t. the optical properties (the "alpha" coefficient), but do *not* significantly change w.r.t the infrared emission properties (the "epsilon" coefficient), including the coatings used on Pioneer. Therefore, your assumptions are irrelevant.

But bringing back to your original point before you distracted... you wondered why analysts could not know the thermal/optical properties of the Pioneer coatings exactly today. I guess you concede now that it's more difficult than you first wondered.


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.

Still 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.

"Most folk?" That's a rather unsubstantiated throwaway claim. It was *you* who claimed that everybody except for Turyshev et al 2012 had ignored the thermal origin, and I had to point out the error of your statement.


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. ...

Non-sequitur. Your statement doesn't make it any easier for a Doppler analyst to reconstruct how the data analysis was done with early data.

And... if you read Anderson's paper, the discrepancy was clearly noted.... in the 1980s far after the spacecraft had passed 20AU. There is nothing in the paper that I can find which references earlier times, aside from the figures you point out of unknown provenance.


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.

Exactly. In the early 1970s, the computing power did not exist to do the in-depth analysis required. The operational need did not exist either. But I see now that you understand that the process is not just about physical laws, but something more.

Which raises some questions here.
What data was plugged into the 2012 Turyshev computer simulation?
The answers are in the Turyshev 2012 paper and its predecessors.

Were the RTG emissions and solar radiation pressures correctly
represented?
Discussed in the Turyshev 2012 paper. "Correct" is a matter of tolerance.

Or were they in fact mismodeled as was the
assumption regarding Anderson's work?
Thanks for the loaded question. Anderson et al did not "mismodel" anything intentionally. The level of fidelity was lower and they did not have the thermal data available at the time required to check, which Turyshev et al did have by 2012.


Does the simulation software contribute toward the outcome? If
so, what was the programmer's information source?

The software is validated against all the missions supported by JPL for radiometric navigation, and the thermal modeling software is standard in the industry. That's why I say it has been validated: it has successfully been used thousands of times to correctly predict temperatures and emission profiles of equipment under test. And, let's not forget that Anderson et al 2002 compared multiple independent software suites, to guard against software errors.

Thermal modeling software also has many inputs. All the inputs for thermal/optical properties were taken from Pioneer engineering documentation, but error tolerances were also considered. *AND*, then the simulations were validated against actual spacecraft measured temperatures. This temperature record was not readily available for Anderson et al to use in 2001, but was for later work.

In the end it comes down to unconditional belief.

Please. It comes down to a consideration of an analysis using established techniques, which has been validated against known data (both other spacecraft and Pioneer itself). There are mountains of documentation on this, which you ignored or barely skimmed over. It's easy for you to just cast out that claim without substantiation, and I reject it.


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

Again, no response.


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.

Again, no response.

...
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.

Who acknowledges it? As I noted above, aside from the figures from unknown sources which you care to reproduce deceptively (see above), Anderson et al 2002 do not mention an "onset" in the paper.

Again, I note that Anderson's claim is that the Pioneer anomaly is consistent with being constant. There was no evidence in the data available for something varying with time. This completely undercuts your own conclusion.

CM
PS.:
.. could somebody give to me the email address of Mauro De Benedetto , rocket trajectory 'analist ?

.... are you again there ? .... consider the point of max anomaly or the point of max changement of anomaly ! .. and so you understand the uselessness to discuss around the RTG or similar things for resolving the Pioneer anomaly .. i think ..