[amsat-bb] Re: ARISSat-1 02.55

[Phil Karn]

On 8/3/11 8:39 PM, g0mrf at aol.com wrote:

> Apx. 6 second spin period puts deep nulls in transmitted signal. -
> Not sure if this is due to linear polarisation of my receive antenna
> or blockage from spacecraft.

Since we don't have video of the actual deployment we don't know how it
was turning at release.

But remember the physics of this. Any body that isn't absolutely rigid
will eventually settle down to a stable spin about the axis with the
greatest moment of inertia. That configuration minimizes kinetic energy
while still conserving angular momentum.

Although ARISSat-1 doesn't have any nutation dampers that I'm aware of,
the slightest flexing of the structure, the antenna (singular), even
tiny movements of the cables inside, will dissipate energy and convert
any complex tumbling motion into a smooth spin about the preferred axis.
That axis includes the antenna, so it shouldn't fade due to spinning.

So it may simply take some time to settle down into a stable spin
without frequent deep fading.

Phil