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Gravitational Doppler



 
 
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  #11  
Old July 26th 06, 05:38 PM posted to sci.astro,sci.physics
Lester Zick
external usenet poster
 
Posts: 735
Default Gravitational Doppler

On 26 Jul 2006 01:56:51 -0700, "George Dishman"
wrote:


Lester Zick wrote:
On Tue, 25 Jul 2006 10:42:09 +0100, "George Dishman"
wrote:

I'll coalesce my replies:


"Lester Zick" wrote in message
.. .
On Mon, 24 Jul 2006 22:38:04 +0100, "George Dishman"
wrote:
"Lester Zick" wrote in message
...
On 24 Jul 2006 05:20:36 -0700, wrote:
...

Lester, the original Anderson paper is he

http://www.arxiv.org/abs/gr-qc/0104064

That's the abstract, there should be a PDF option
on the page that gives you the full document (I have
some preferences set so I get PDF by default, it
might be an option for you).


George, I appreciate the original reference but after several hours
reviewing it am having considerable difficult finding out exactly
where and how the acceleration was measured.


There is a lot in the paper.

The basic technique is that a signal was sent to
the craft, the uplink. When that was received, the
craft was configured to lock its return (downlink)
carrier to an exact multiple of the uplink frequency.
The frequencies of the uplink and downlink were
measured and recorded. The difference is the
Doppler shift which indicates relative speed.


Okay. I remember reading something about this.

The component due to the motion of the Earth
is known and the remainder should indicate the
motion of the craft.

A 'best fit' of the craft motion to the measured
Doppler is then produced using an optimum
initial velocity and the known gravitational
acceleration of all major solar system bodies.
The Doppler due to that motion is then predicted.
In theory of course it should be a perfect match
to what was received since the trajectory was
fitted to the data but it doesn't quite work. The
reminder is plotted in Figure 8 and shows an
apparent linearly increasing discrepancy in the
velocity of the craft compared to that modelled,
i.e. a constant acceleration.


Got it. So we're measuring velocity through linear doppler and
measuring a constant change in velocity. Okay. I understand.

As a philosophical aside of problematic interest, last night I got to
wonder how we actually measure intangibles like velocity and
acceleration and decided it really all comes down to measuring the
position of different things such as physical location in relation to
one another and in relation to the hands of clocks etc.

I see numerous references
to variances in acceleration and about everything else under the sun
but nothing that shows what measured acceleration. For instance was it
an accelerometer of some kind? Or was the measure of acceleration
simply inferred from some other measurement? If you could tell me or
at least point me to a page reference in the document it would be much
appreciated.


Section II, D on page 5 gives a description of the
overall communications system, Section III, A on
page 8 describes the measurement equipment
and Section III, B, 1 on page 9 explains the
method. This gives speed and acceleration is
inferred as explained above.

Unfortunately, direct range measurement wasn't
available from Pioneer 10 due to problems with
the craft losing lock when it was attempted.


Well Anderson spends considerably more time discussing ranging for
Pioneer 11 so I got a little confused.

What I'd like to do is spend a few days considering this issue and try
to evaluate the numbers I use versus the anomaly as stated in terms of
acceleration. I'm quite confident we're actually looking at the same
values cast in different form and that the stated value for the
anomaly in terms of acceleration and the distances I use are mutually
consistent with each other at any given point in time. I can' imagine
the Times did their own calculations so I expect Anderson or JPL did
the calculations for the particular year covered. In any event my
calculation is accurate to the precision stated and should continue to
be consistent with the anomaly as stated in terms of acceleration as
long as it remains constant.

Lester Zick
~v~~
  #12  
Old July 27th 06, 06:22 PM posted to sci.astro,sci.physics
Lester Zick
external usenet poster
 
Posts: 735
Default Gravitational Doppler

On 26 Jul 2006 01:56:51 -0700, "George Dishman"
wrote:


Lester Zick wrote:
On Tue, 25 Jul 2006 10:42:09 +0100, "George Dishman"
wrote:

I'll coalesce my replies:


"Lester Zick" wrote in message
.. .
On Mon, 24 Jul 2006 22:38:04 +0100, "George Dishman"
wrote:
"Lester Zick" wrote in message
...
On 24 Jul 2006 05:20:36 -0700, wrote:
...

Lester, the original Anderson paper is he

http://www.arxiv.org/abs/gr-qc/0104064

That's the abstract, there should be a PDF option
on the page that gives you the full document (I have
some preferences set so I get PDF by default, it
might be an option for you).


George, I appreciate the original reference but after several hours
reviewing it am having considerable difficult finding out exactly
where and how the acceleration was measured.


There is a lot in the paper.

The basic technique is that a signal was sent to
the craft, the uplink. When that was received, the
craft was configured to lock its return (downlink)
carrier to an exact multiple of the uplink frequency.
The frequencies of the uplink and downlink were
measured and recorded. The difference is the
Doppler shift which indicates relative speed.

The component due to the motion of the Earth
is known and the remainder should indicate the
motion of the craft.

A 'best fit' of the craft motion to the measured
Doppler is then produced using an optimum
initial velocity and the known gravitational
acceleration of all major solar system bodies.
The Doppler due to that motion is then predicted.
In theory of course it should be a perfect match
to what was received since the trajectory was
fitted to the data but it doesn't quite work. The
reminder is plotted in Figure 8 and shows an
apparent linearly increasing discrepancy in the
velocity of the craft compared to that modelled,
i.e. a constant acceleration.

I see numerous references
to variances in acceleration and about everything else under the sun
but nothing that shows what measured acceleration. For instance was it
an accelerometer of some kind? Or was the measure of acceleration
simply inferred from some other measurement? If you could tell me or
at least point me to a page reference in the document it would be much
appreciated.


Section II, D on page 5 gives a description of the
overall communications system, Section III, A on
page 8 describes the measurement equipment
and Section III, B, 1 on page 9 explains the
method. This gives speed and acceleration is
inferred as explained above.

Unfortunately, direct range measurement wasn't
available from Pioneer 10 due to problems with
the craft losing lock when it was attempted.


George, since we've clarified what is being measured and how in terms
of the Pioneer anomaly, let me run something else by you which has
been bothering me since I first read about it a year and half ago. At
that time what I saw were three numbers: the reported anomaly itself
a_p=8x10^-8 cm/secsec and of course the numbers I used to calculate
d/D=D/c D=219,000,000 miles per year and d=8,000 miles per year.

Now when I see the anomaly a_p called acceleration and reported in
units of cm/secsec, my first reaction is that what we're looking at is
an acceleration resulting from some kind of force such as gravitation.
However I don't see this anomaly in those terms and that's been the
source of my confusion. In other words I don't see this acceleration
acting on a stationary Pioneer to cause it to begin to move. So
although we're technically looking at a change in velocity, in my own
estimation the actual measure of the anomaly should be reported in
neutral composite terms as 8x10^-8 per sec superimposed on velocity
period.

In other words I see the anomaly in relative rather than absolute
terms indicated by the use of cm/secsec as units. In fact the reported
value for the anomaly as a constant doesn't even makes sense unless
velocity is measured in cm/sec and the anomaly is taken as a fraction
of velocity.

Lester Zick
~v~~
  #13  
Old July 28th 06, 08:41 AM posted to sci.astro,sci.physics
George Dishman[_1_]
external usenet poster
 
Posts: 2,509
Default Gravitational Doppler


Lester Zick wrote:
On 26 Jul 2006 01:56:51 -0700, "George Dishman"

The basic technique is that a signal was sent to
the craft, the uplink. When that was received, the
craft was configured to lock its return (downlink)
carrier to an exact multiple of the uplink frequency.
The frequencies of the uplink and downlink were
measured and recorded. The difference is the
Doppler shift which indicates relative speed.

The component due to the motion of the Earth
is known and the remainder should indicate the
motion of the craft.

A 'best fit' of the craft motion to the measured
Doppler is then produced using an optimum
initial velocity and the known gravitational
acceleration of all major solar system bodies.
The Doppler due to that motion is then predicted.
In theory of course it should be a perfect match
to what was received since the trajectory was
fitted to the data but it doesn't quite work. The
reminder is plotted in Figure 8 and shows an
apparent linearly increasing discrepancy in the
velocity of the craft compared to that modelled,
i.e. a constant acceleration.

....
Section II, D on page 5 gives a description of the
overall communications system, Section III, A on
page 8 describes the measurement equipment
and Section III, B, 1 on page 9 explains the
method. This gives speed and acceleration is
inferred as explained above.

....
George, since we've clarified what is being measured and how in terms
of the Pioneer anomaly, let me run something else by you which has
been bothering me since I first read about it a year and half ago. At
that time what I saw were three numbers: the reported anomaly itself
a_p=8x10^-8 cm/secsec and of course the numbers I used to calculate
d/D=D/c D=219,000,000 miles per year and d=8,000 miles per year.

Now when I see the anomaly a_p called acceleration and reported in
units of cm/secsec, my first reaction is that what we're looking at is
an acceleration resulting from some kind of force such as gravitation.


That is how it apears, though gravitation as a cause is
unlikely because of the constancy. Initial thoughts
included things like a gas leak or uneven radiation from
the RTGs. They emit about 2kW of heat and if that was
split as 1032W away from the Sun and 968W towards,
it would explain the anomaly. However they cannot
justify why the paint emission characteristics would
differ by that amount.

Another possibility would be if it was ploughing through
interplanetary dust producing a drag effect, but the
amount of dust is higher than the maximum allowed by
other measurements.

However I don't see this anomaly in those terms and that's been the
source of my confusion. In other words I don't see this acceleration
acting on a stationary Pioneer to cause it to begin to move.


The trouble is that the craft was moving at about
12km/s all the time. If the cause was RTG radiation,
the acceleration would be the same if Pioneer were
stationary while dust as a cause would produce no
acceleration on a stationary craft.

So
although we're technically looking at a change in velocity, in my own
estimation the actual measure of the anomaly should be reported in
neutral composite terms as 8x10^-8 per sec superimposed on velocity
period.


Yes, they say they debated how to report it for some
time. Since what is measured is the Doppler frequency,
the neutral version is the value of 6*10^-9 Hz/s they give
on page 20.

In other words I see the anomaly in relative rather than absolute
terms indicated by the use of cm/secsec as units. In fact the reported
value for the anomaly as a constant doesn't even makes sense unless
velocity is measured in cm/sec and the anomaly is taken as a fraction
of velocity.


No, that makes an assumption that the acceleration
would be zero at zero speed which would not be the
case if radiated waste heat is the cause. In the case
of radiation pressure or gas leaks, the acceleration is
independent of speed while for dust drag it would be
proportional to the square of the speed.

Whatever the behavior as a function of speed, in
practice the anomaly was constant so the value of
your 'd', the distance discrepancy, is given by

d = 1/2 * a_P * t^2

where t is the time since 1 Jan 1987. It means that
d/D is far from constant while v/c varied little. Of
course even that assumes that the cause involved
the motion of the craft. Anderson et al allow for the
possibility that the anomaly affects the signal
frequency directly but the analysis suggests this is
unlikely.

George

 




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