A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

"Pioneer anomalous acceleration" and Cassini



 
 
Thread Tools Display Modes
  #1  
Old September 29th 03, 10:50 PM
Jonathan Silverlight
external usenet poster
 
Posts: n/a
Default "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"
Remove spam and invalid from address to reply.
  #2  
Old September 30th 03, 10:39 AM
Mike Dworetsky
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini



"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

(Remove "pants" spamblock to send e-mail)


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

of
void"
Remove spam and invalid from address to reply.



  #3  
Old October 7th 03, 06:07 PM
greywolf42
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

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


  #4  
Old October 8th 03, 05:00 PM
Craig Markwardt
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini


"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
  #5  
Old October 9th 03, 08:40 PM
greywolf42
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

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


  #6  
Old October 10th 03, 12:11 AM
Dag Oestvang
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

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.


  #7  
Old October 10th 03, 06:42 PM
Jonathan Silverlight
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

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.
  #8  
Old October 29th 03, 04:50 AM
greywolf42
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

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
  #9  
Old October 29th 03, 09:22 AM
Craig Markwardt
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini


(greywolf42) writes:

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

[ snip for brevity ... ]
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.


*You* are incorrect. At its literal level, the Bertotti et al paper
deals with the non-gravitational accelerations due to solar radiation
pressure and RTG emission (see paragraphs 9 and 10). Further more, it
of course deals with the gravitational accelerations due to other
solar system bodies [this is implicit in the Methods section, and the
mention of JPL's Orbit Determination Program, which integrates the
complete equations of motions including all known forces.]

And at the core level: *of course* Bertotti must model all forces on
the spacecraft! As they point out in equation 2, the observable
depends sensitively on b and db/dt, which are time-variable due to the
spacecraft motion. The only way to determine the spacecraft motion is
to integrate the equations of motion with a set of modeled
accelerations/forces. This is obvious from the paper, but I can also
speak from direct experience, that such an approach is necessary.


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.


Incorrect statement. The rms residuals in the doppler signal directly
tie to the confidence region for the PPN parameter, gamma, via
equation 2. The Doppler residuals are a consequence of several
factors including: intrinsic measurement noise, and intrinsic force
modeling error. Therefore, if the authors had missed a significant
force/acceleration in their model, it would have shown up in the
Doppler residuals, and in turn worsened the confidence bounds on
gamma. The Doppler residuals are directly related to the precision of
gamma, and thus, the conclusions of the paper.

CM

  #10  
Old October 29th 03, 09:26 AM
Jonathan Silverlight
external usenet poster
 
Posts: n/a
Default "Pioneer anomalous acceleration" and Cassini

In message , greywolf42
writes
Jonathan Silverlight
wrote in message
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.


Which part of "An important contribution to the frequency shift is due
to non-gravitational forces acting on the spacecraft" do you have a
problem reading?

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.


"The anisotropic thermal emission of the spacecraft" (same paragraph).
They had to take it into account, even though it's much smaller than the
relativistic 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)



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


I'm not saying it is. I'm saying that Anderson et al. modelled Pioneer
and found a residual frequency drift. Bertotti et al. modelled Cassini
and found no drift (or possibly a very tiny one). So something is
different.
--
Rabbit arithmetic - 1 plus 1 equals 10
Remove spam and invalid from address to reply.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 07:43 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.