[amsat-bb] SEC: UNCLASSIFIED - AO-40 wobbles (was: Plans for April-June 2001)

["Ellis, Peter R." <Peter.Ellis@xxxxxxxxxxxxxxxxxx>]

Just remembering my flying training... and I am NOT an aeronautics engineer.

Could the wobbles be caused by the spacecraft's antennas not being QUITE
symmetrical, and as it flies through VERY thin the atmosphere - - spinning -
- the asymmetric drag from the various antenna structures creates a slight
imbalance in the forces so that the wobble increases?

*	AO-40's antennas and other protrusions are NOT symmetrical from a
'drag' point of view. (Just look at a photo of it!)
*	Asymmetry can be bad and usually is !
*	Drag is not completely 'intuitive' - - what looks 'draggy' probably
is, but some things may actually be okay / low-drag.
*	Drag causes a flying body to change direction towards the greater
drag.
*	AO-40 is spinning, but this does not mean that the drag can be
'averaged' - - because it is 'pointing' and so the drag terms must be
applied to its profile as it 'flies' in various apparent aerodynamic
configurations. (Worst case image... Think of a 747 flying by pointing in
the same direction throughout a flying day: Straight ahead from LA to
Denver, then at an angle of about 60 degrees to the wind as it goes on to
Chicago, then almost tail-first to Seattle, and side-on back to LA.) 

Peter Ellis
VK1KEP
Canberra, Australia

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