Re: Pioneer Anomoly

On Fri, 24 Jun 2005 15:05:34 +0100, "George Dishman"
<george@xxxxxxxxxxxxxxxxx> wrote:

>
>"John C. Polasek" <jpolasek@xxxxxxxxxx> wrote in message
>news:krnmb1hq717rutfupoctgc5j20teqi8tfm@xxxxxxxxxx
>> On Fri, 24 Jun 2005 00:03:33 +0100, "George Dishman"
>> <george@xxxxxxxxxxxxxxxxx> wrote:
>>>"John C. Polasek" <jpolasek@xxxxxxxxxx> wrote in message
>>>news:otbkb1t2ko0hf53jkis7chjrdvvodl0fq5@xxxxxxxxxx
>...
>>>> I have half read the paper again and I saw the statement that when P10
>>>> got the signal it amplified it and re scaled it and retransmitted it.
>>>> I find that hard to believe, when it seems so much cleaner to trigger
>>>> a local oscillator and get a clean primary signal back to earth. I
>>>> believe it makes a big difference.
>>>> I am continuing to investigate.
>>>
>>>That's what they do, there is an on-board high
>>>stability oscilator which can be phase-locked
>>>to the uplink carrier. The PLL includes a fixed
>>>ratio divider so that the downlink frequency is
>>>exactly related to the uplink.
>>
>> George and Jonathan:
>> If the downlink is phaselocked to the uplink (plus the divider) how
>> are you expected to get doppler drift?
>
>Suppose the craft is moving away from Earth. There
>is a Doppler red shift on the uplink. The craft
>multiplies that frequency by 240/221 and sends it
>back. There is another Doppler red shift on the
>downlink. If the Earth were at rest, the shift is
>twice that on either link alone.

These would be adjusted out, obviously.
..
>> That clock in space has to be a
>> free agent. It doesn't even seem to be a valuable complication.
>
>They use both methods, free running and transponding.
>The stability of the free clock is not as good as
>when it is locked to the ground based maser reference
>system.

How can a cesium (or other) clock in zero gravity not be good enough.
What is there to throw it off?

>>>The text discusses the meaning of "phase coherent"
>>>in the third paragraph of section 3.1, and there
>>>is a more general description in section 2.4.
>>
>> I have a much more serious question and that is that I could not find
>> in Andersons paper any record of the actual doppler shifts
>
>The actual shift varies minute by minute. You
>have worked out part of it below but try these
>as well, they will put the problem into
>perspective:
>
>The craft is leaving the Solar system at about
>12km/s. What shift does that produce?

These would be adjusted out, obviously. It's what's meant by
residuals.

>The Earth orbits the Sun at about 30km/s. That
>produces a sine wave frequency shift with a
>period of one year. What amplitude?
>
>The Earth rotates once per sidereal day. At
>the latitude of the DSN stations, the speed
>is about 350m/s. What is amplitude of the
>resulting shift?

Compensated.

>> and can't
>> understand their residuals.
>
>Using the Doppler, they compute the most
>likely trajectory for the craft. The
>residuals are the difference between the
>difference between the measured value and
>the predicted value at each measurement
>time. The "most likely trajectory" is that
>which produces the least total residuals.
>
>> But let me point out an outrageous obstacle.
>>
>> The downlink is at 2.295Ghz and Ap is 8.74x10^-10m/ss.
>> Doppler shift for velocity v is given by
>> DS = F x v/c hz
>> Doppler drift is given using dv/dt which in our case is Ap:
>> DSdot = F x Ap/c hz/second
>> DSdot = 6.7 x 10^-9 Hz/second
>> Time for change of 1 Hz:
>> T/hz = 1Hz/DSdot = 1.5 x 10^8 seconds = 4.7 years!!
>> A change of 1Hz in nearly 5 years?
>> I have probably made an error somewhere. Help me out.
>
>Your only error is that the shift is doubled
>because it applies on both the uplink and
>downlink. The residuals shown in Figure 8
>(page 36) amount to about 3Hz in 8 years.

But in one place he says the uplink is Doppler corrected before
transmission. I did not see a Fig. 8 on page 36 but did see Fig. 7
page 19 in Anderson paper 0104064 showing about 8e-13km/ss.

>Craig Markwardt independently repeated the
>calculations developing his own software and
>his results are here:
>
>http://www.arxiv.org/abs/gr-qc/0208046
>
>Figure 2 shows the residuals after also
>assuming a constant acceleration A_p.
>
>As you can see, the spread is of the order
>of 4 mHz (yes, I do mean 0.0042 Hz !).
>
>Going back to your original point, the
>frequency of the on-board oscillator would
>need to be accurate to 1 part in 10^15 even
>after many years in space, and that's not
>feasible. Without the transponder, the
>results would be indistinguishable from a
>slow drift in the oscillator due to aging.
I agree, with the transponder the doppler would be double the value.
Unfortunately that also takes out any effect the gravitational field
would have on the Pioneer clock. That is very probably where the
secret is. Do you agree that gravitational effects woud be washed out?
>George
>
John Polasek
http://www.dualspace.net
.

Relevant Pages

  • Re: Pioneer Anomoly
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  • Re: Its all so simple
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    (sci.physics.relativity)