"Pioneer anomalous acceleration" and Cassini

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.
Does that mean the question is settled, or isn't their measurement
sufficiently sensitive?
--
"Forty millions of miles it was from us, more than forty millions of miles of
void"
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"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.
Does that mean the question is settled, or isn't their measurement
sufficiently sensitive?

The question of whether all spacecraft will experience an anomalous
acceleration between Jupiter and Saturn has been answered (the answer is
NO).

Their measurements and models for acceleration mechanisms are much more
sensitive than the pioneer data, in part because the quality of the
transmitter is much better. Also the spacecraft is much more massive, so
small local forces will not shift it by much.

The explanation of the anomalous acceleration of Pioneer remains unknown but
as you know, many workers in this field believe it is due to some small
radiative effect not correctly accounted for or an extremely small leak of
propellant.

Others still hope there is some now physics to be discovered.

--
Mike Dworetsky

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--
"Forty millions of miles it was from us, more than forty millions of miles
of
void"
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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.

Does that mean the question is settled, or isn't their measurement
sufficiently sensitive?

The question was settled years ago. There *is* definitive anomalous
acceleration in pioneer and the voyagers. No theoretical explanation has
yet been settled on.

greywolf42
ubi dubium ibi libertas

"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

Craig Markwardt wrote in message
news

"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.


And my reading of your above statement is that there is no such conclusion
contained within the paper. The paper is nothing more or less than a
calculation of the PPN parameter, gamma during a single Solar conjunction.

There are no modelling of forces on the spacecraft in the paper -- construct
or otherwise.

greywolf42
ubi dubium ibi libertas

In message , greywolf42
writes
Craig Markwardt wrote in message
news

"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.


And my reading of your above statement is that there is no such conclusion
contained within the paper. The paper is nothing more or less than a
calculation of the PPN parameter, gamma during a single Solar conjunction.

There are no modelling of forces on the spacecraft in the paper -- construct
or otherwise.

Have you actually looked at the paper??
They wouldn't be able to see anything without accurate modelling of the
gravitational and non-gravitational forces on the spacecraft.
It's the latter which are much more interesting here - solar radiation
and the anisotropic thermal emission from the spacecraft, which is the
prime suspect in the Pioneer acceleration.

Quoting
"Deriving this acceleration from a model of the spacecraft is a
difficult task; but its estimation from Doppler measurements, combined
with attitude data, is routinely carried out for spacecraft navigation
with good and consistent accuracies. The largest component (along the
Earth-spacecraft axis, _pushing towards the Earth_
[my emphasis]
) is about 3 x 10^-9 m s^2..... This component has been determined with
a formal error of ~3%".

Bertotti et al. figure 3 shows Doppler residuals of about +- 4 x 10^-4
Hz over the 30 day period of solar conjunction, and their RMS value is
1.2 x 10^-4. This works out to about 5 x 10^-11 Hz/s, much less than
the figure Anderson et al. found (6 x 10^-9 Hz/s)
--
"It is written in mathematical language"
Remove spam and invalid from address to reply.

Jonathan Silverlight wrote in message ...
In message , greywolf42
writes
Craig Markwardt wrote in message
news

"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.


And my reading of your above statement is that there is no such conclusion
contained within the paper. The paper is nothing more or less than a
calculation of the PPN parameter, gamma during a single Solar conjunction.

There are no modelling of forces on the spacecraft in the paper -- construct
or otherwise.

Have you actually looked at the paper??

Yes.

They wouldn't be able to see anything without accurate modelling of the
gravitational and non-gravitational forces on the spacecraft.

You are incorrect. The paper does not deal with forces on the
spacecraft at all. Please read it.

It's the latter which are much more interesting here - solar radiation
and the anisotropic thermal emission from the spacecraft, which is the
prime suspect in the Pioneer acceleration.

But irrelevant to this paper.


Quoting
"Deriving this acceleration from a model of the spacecraft is a
difficult task; but its estimation from Doppler measurements, combined
with attitude data, is routinely carried out for spacecraft navigation
with good and consistent accuracies. The largest component (along the
Earth-spacecraft axis, _pushing towards the Earth_
[my emphasis]
) is about 3 x 10^-9 m s^2..... This component has been determined with
a formal error of ~3%".

Bertotti et al. figure 3 shows Doppler residuals of about +- 4 x 10^-4
Hz over the 30 day period of solar conjunction, and their RMS value is
1.2 x 10^-4. This works out to about 5 x 10^-11 Hz/s, much less than
the figure Anderson et al. found (6 x 10^-9 Hz/s)


The above is not related to the conclusion of the paper.

greywolf42
ubi dubium ibi libertas

Craig Markwardt wrote:

"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.


More precisely; due to the uncertainity in the modelling
of the thermal output of the RTGs one cannot say if
an anomalous acceleration is present in the Cassini data.

The given residual acceleration of about
a_r=-27*10^-8 cm/s^2 is _consistent_ with the
presence of the Pioneer anomaly though.
See gr-qc/0308010 for more details.

"greywolf42" wrote in message ...
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.

Does that mean the question is settled, or isn't their measurement
sufficiently sensitive?

The question was settled years ago. There *is* definitive anomalous
acceleration in pioneer and the voyagers. No theoretical explanation has
yet been settled on.

Finally gathered the courage to tentatively suggest that when photons
are emmitted, they give a 'recoil' against the source. If radiation
from within the craft is directed in a particular direction, a thrust
might occur. (I thought that this would be so insignificant as to be
immesurable and undetectable, but maybe not)
What would happen to a high-power laser carefully suspended- any
chance of detecting an observable thrust counter to beam direction???

Jim G

"Jim Greenfield" wrote in message
om...
"greywolf42" wrote in message
...

The question was settled years ago. There *is* definitive anomalous
acceleration in pioneer and the voyagers. No theoretical explanation
has
yet been settled on.

Finally gathered the courage to tentatively suggest that when photons
are emmitted, they give a 'recoil' against the source.

Yes, each photon carries a momentum proportional to
its frequency.

If radiation
from within the craft is directed in a particular direction, a thrust
might occur. (I thought that this would be so insignificant as to be
immesurable and undetectable, but maybe not)

The data from Pioneer is sent back by radio. The power is
nominally 8W, a little more than a mobile phone. The radiation
pressure from the beam is about 13% of the magnitude of the
anomaly but the beam pushes the craft away from the Earth while
the anomaly is an acceleration towards the Earth. This is why
asymmetric thermal radiation from the RTGs was looked at as a
possible explanation, they emit a couple of kW altogether. The
trouble was that nobody could figure out how to explain the
asymmetry.

What would happen to a high-power laser carefully suspended- any
chance of detecting an observable thrust counter to beam direction???

Yes, or turned around, shining a laser on a solar sail can give
it thrust. The effect can also be used to suspend individual
atoms in a laser beam.

George