Re: Anom Accel of Pioneer 10 for v>(GM/r)^1/2

Craig Markwardt replied to Jonathan Silverlight:
 
>> But is the question still open, or is anisotropic thermal
>> emission still the best candidate to explain the Pioneer
>> effect? Marmet doesn't mention the conventional explanations.
> 
> I've looked into this a little more.  From my analysis, there is
> some evidence for a change in the acceleration over time.  This
> is almost enough to be consistent with the decrease in the amount
> of power consumption in the Pioneer 10 equipment compartment.
> I think it is quite possible there could be anisotropic emission
> from this compartment, or via some other, similar means, which
> accounts for the acceleration.
 
Craig,
 
I posted this on February 22, 2002, here in sci.astro, in reply
to Bruce Sterling Woodcock:
 
  > Presently some 2000W of RTG heat must be dissipated,
  > so it would seem that would be enough.  But the problem is the
  > RTGs are located at the ends of the booms, and they only see
  > the antenna "edge on", subtending an angle of about 1.5% of 4
  > steradians.  That means at most 30W of power could be impacting
  > it.  Moreover, every RTG is not a spherical black body, but
  > rather has fins that are "edge on" to the antenna, which means
  > only 2.5% of the surface area of the RTG is actually facing the
  > antenna.  The RTG mechanism doesn't provide enough power to
  > explain the anomalous acceleration.
  
  Looking at photographs of the spacecraft leads me to wonder
  whether the analysis you quote is correct.  First off, you said
  "an angle of about 1.5% of 4 steradians".  That was probably
  intended to be "4 pi steradians", meaning the total sphere.
  By eyeball estimate, I'd say that the antenna and other parts
  of the spacecraft sunward of the RTGs subtend a solid angle of
  about 5% of a sphere, rather than 1.5%.  I estimate that 20%
  of the RTGs are visible to the sunward parts of the spacecraft,
  rather than 2.5%.  Those are pretty big differences.  Perhaps
  my estimates are that far off, or perhaps someone fouled up
  the analysis.  Take a look at some photos of Pioneer, and see
  if you don't agree that the figures you give seem way too low.
  
  Maybe it still isn't enough to cause the anomaly.  But it looks
  like a very good possibility.
 
Bruce replied, in part:
 
  The RTG's have fins on them that are "edge-on" to the antenna.
  The actual surface area that faces the antenna is much smaller
  because of it.
  
And I replied to Bruce:
 
  Yes, I can see that.  It is why I estimate that only 20% of
  the RTG surface area is visible to the back side of the antenna
  dish and other parts of the spacecraft sunward of the RTGs,
  rather than the approximately 45% that would be visible if they
  were plain cylinders.
 
Any comments?
 
  -- Jeff, in Minneapolis
 
Subtract 1 from my e-mail address above for my real address.
.