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Thread: Fly By Speed Increment Anomalies ?

  1. #1 Fly By Speed Increment Anomalies ? 
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    How was the speed anomalies of the space probes NEAR, GALILEO, ROSETTA etc. measured

    I often hear that Doppler Effect was used.
    But how does that work ?
    Once I hear a atomic clock was ion board the Pioneer 10 and 11 space probes.
    A signal was send from earth and to the pioneer probes, - asking what time it is (on board) , the atomic clock on board replied, - and the signal was turn back to Earth with that information.
    Now it was easy to calculate the distance based on the time it took the signal to return.
    But this has (so far I understand) nothing with Doppler Effect measurement to do.
    1.What is this time calculation technic called ?
    2.So fare I understand Doppler it is to measure the change of wavelength of a certain frequency that is send from the space probe to the Earth - Correct ?
    3.And this doesn't involve time measurement of any kind ?
    4.Was different technique used for measuring the Space Probes anomalies ? ( I read somewhere that only Doppler was used when discovering the flyby anomalies )


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  3. #2  
    Brassica oleracea Strange's Avatar
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    The Doppler effect (Wikipedia, the free encyclopedia) is a change in frequency caused by the relative motion of the source of a signal. You can hear it when cars drive past you: the pitch is higher as they approach and then lower as they recede.

    The radio signals from satellites and space probes are tracked by a number of different stations all around the Earth. Because these are receiving signals from moving objects, they have to take the Doppler effect into account (by listening on a slightly different frequency than for a stationary transmitter). By monitoring the difference in frequency, they can work out the relative speed of the transmitter. (GPS receivers have to do the same thing for the signals from GPS satellites.)

    I don't know if there is a specific name for this technique. And I don't know if any other techniques are used (the Doppler effect is the most direct method of speed measurement I can think of, off the top of my head. It is also what is used by police speed traps.)


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    Some places at the internet I have read the flyby anomalies are of the order 10e-4m/s^2
    Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller.

    So what is correct
    Last edited by Bjarne; January 30th, 2014 at 09:57 AM.
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