Re: Pioneer radio force--believable?
- From: Craig Markwardt <craigmnet@xxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: 22 Jan 2006 13:40:41 -0600
John C. Polasek <jpolasek@xxxxxxxxxx> writes:
> Is it really possible for an 8 watt radio to create thrust sufficient
> to affect the Pioneer anomaly by 14%?
>
> The Pioneer anomaly is an acceleration back toward the Sun of
> 8.74e-10m/s^2, not explainable via the current "standard model".
>
> Question is, should we take into account the theoretical radio force
> from the 8 watt transmitter pushing back from the Sun according to
> Acc =P/mc = 8 watts/c*241kg
> Acc = 1.1 e-10m/s^2
> which would make an anomaly of 7.64 increase to 8.74 after giving
> weight to Acc, the radio thrust. Is there experimental backing for
> this force?
>
> The answer is quite important, because the change from 8.74 to 7.64
> has major consequences.
Yes, radiation pressure is a well-tested and well-measured component
of electromagnetic theory, so its nature is believable.
Of course the spacecraft's motion is changed by the solar radiation
pressure, so we know that radiation effects must be considered. The
difference is that the solar radiation pressure varies from being
dominant in the inner solar system to almost negligible at the point
where the Pioneer "anomaly" was measured. The Pioneer traveling wave
tube emitter is designed to have a constant power output.
The emitter output is small but not insignificant. It is important to
account for its radiation pressure, which has been done.
One might ask the question, could the radiation pressure from the
emitter be *equal* to the anomaly, and the answer is almost certainly
not. One can never extract *more* momentum than there is power
density in the radiation. To account for the anomaly, the power of
the emitter would need to be ~7-10 times higher than designed, but
this is not really possible: the spacecraft RF system would have been
calibrated in ground testing to achieve the designed power levels.
Also, spacecraft power budget constraints do not really allow for the
possibility of more-than-designed output, especially in the extended
phase of the mission when the RTGs were producing bare-bones power.
CM
.
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- Pioneer radio force--believable?
- From: John C . Polasek
- Pioneer radio force--believable?
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