"greywolf42" writes:

Jonathan Silverlight wrote
in message ...


There's an article in the current issue of Nature that seems relevant to
the Pioneer anomalous acceleration question ("A test of general
relativity using radio links with the Cassini spacecraft" B Bertotti, L
Iess and P Tortora, Nature vol 425. No. 6956 p. 374,
doi:10.1038/nature01997)
AFAICS they have accurately modelled emission from the RTGs and they
don't see any unexplained acceleration.

They haven't looked for anomalous acceleration with this experiment. The
referenced experiment measures the time-delay of the signal in a
gravitational field. Nothing more.

Incorrect. The referenced Cassini experiment, as with all radiometric
Doppler tracking experiments, measures the Doppler shifts of the
carrier due to the motion and other intervening effects. The time
delay is not measured (i.e., it is not a ranging experiment). The
Shapiro effect enters into the observable as the *time rate of change*
in the signal travel time (including relatistic effects).

It is also incorrect to say that the Cassini experiment does not
measure an "anomalous" acceleration. By construction, the experiment
requires a modeling of all forces on the spacecraft, "anomalous" or
not. My reading of the article is that no anomalous forces were
required.

CM