Jonathan Silverlight wrote
in message ...
In message , greywolf42
writes


{replaced invisibly snipped quote from paper}
==========================
Well, the complete abstract is:
"Radio Doppler data from the Cassini spacecraft during its solar conjunction
in June 2002 can be used to test General Relativity. In terms of the
standard post-Newtonian parameter , the result is gamma - 1 = (-4.8 +- 5.7)
x 10^-5, including both random and systematic error (sic). Einstein's
theory has survived yet another test."

There are two mentions of the Pioneer effect in this paper:

"We include eight parameters in the weighted-least-squares solution: first,
the six initial conditions (state) for the spacecraft trajectory; secondly,
a constant radial acceleration a_r, primarily to account for the spacecraft'
s thermal emission, but also for smaller effects such as unmodeled
solar-pressure, beamed radio emission, and a possible contribution from the
Pioneer anomaly [12]; and finally the relativity parameter gamma."

And:

"Finally, the error in a_r from 27 days of Cassini Doppler data is about two
times better than the result from 11 years of Pioneer 10 Doppler data [12].
However, unlike Pioneer, the result is not anomalous. Both Pioneer and
Cassini are powered by radioisotope thermoelectric generators (RTG), but on
Pioneer they are mounted on booms and radiate the bulk of their thermal
output isotropically into space without reaching the spacecraft. On the
other hand for Cassini, the RTG's are mounted on the spacecraft bus beneath
the high-gain parabolic dish antenna. Their thermal output is controlled by
refection and absorption by the antenna and other spacecraft parts. It is
difficult to model, although it should be directed toward the Earth, as
confirmed by the negative sign in the solution for a_r. However, the
uncertainty in the thermal model overwhelms any plausible application of the
Pioneer anomaly to Cassini."
==========================

In short, there is no way Cassini can be used for evaluation of the
Pioneer
effect. This is because the thermal emissions from Cassini are
non-isotropic, and far greater in magnitude than the expected Pioneer
effect. The statement the Cassini "result is not anomalous" is
completely
misleading. And completely wrong when taken out of context. The result
is
not anomalous only because the Pionner effect cannot be observed by
Cassini,
due to the effect being swamped by difficult-to-model thermal emissions.

Again, the purpose of this measurement was validation of GR's gamma --
not
the Pioneer effect.

I know that.

Then why are you attempting to claim results other than what the paper and
observations were about?

I don't know if the solar opposition experiment has been published, but
the point is that Bertotti et al.

Horsefeathers. The reference under discussion was Anderson and Lau -- not
Bertotti. And the difficulty of modelling the emission is not physically
different for Bertotti than four Anderson and Lau.

But I guess that's why you snipped the quotes from your own reference (for
the second time):

quote a figure for the acceleration
from the RTGs of 3 x 10^-9 m s^-2, with an error of 9 x 10^-11 m s^-2.
That error is about "an order of magnitude" less than the Pioneer
effect.

Not according to Anderson and Lau.

Anderson et al. quote a figure for a_r (the radial acceleration, mostly
due to the RTGs) of -26.7 x 10^-8 cm s^-2, which is essentially the same
when you convert.

Yes. And Anderson and Lau mention that "the uncertainty in the thermal
model overwhelms any plausible application of the Pioneer anomaly to
Cassini."

As Volker Hetzer says, there's a contradiction between the statements
that "the result is not anomalous" and "the uncertainty in the thermal
model overwhelms any plausible application of the Pioneer anomaly to
Cassini". The new measurements are much more accurate than the Pioneer
ones (compare the residuals) and the Pioneer effect doesn't appear.

How are they more accurate? According to Anderson, the measurements
of 'anomalous accelerations' would are 10 times less precise than the gross
effect measured to 2 sig figs on Pioneer. Due to "the uncertainty in the
thermal model" of Cassini.

--
greywolf42
ubi dubium ibi libertas
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