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RE: Changing AO-40's attitude



On Thursday, February 01, 2001 8:56 PM Doug Braun NA1DB said:
> ... This would mean the wheel would have to spin at 8800 RPM,
> which it definitely cannot do!
> ...
> They CANNOT change the total angular momentum of the spacecraft!
> ...
> It's only a few RPM, I believe.

When I want to learn the facts I always go to amsat.org first.  There
you will find an outstanding article covering this subject in detail.
It says:

"Each wheel provides a momentum storage capacity of 15 Nms at 3000 rpm."

"For the AMSAT Phase 3-D mission, three momentum wheels will operate in
a momentum bias mode at a nominal speed of 1000 rpm, giving the
satellite dynamic stiffness. Changing wheel speeds can both reorient the
spacecraft and compensate for disturbing forces such as solar pressure.
The momentum of the wheels has to be dumped at a speed of 3000 rpm,
which is achieved by generating an external torque at the perigee of the
satellite orbit at a height of 4000 km. This is done with magnetorquers
operating in the Earth magnetic field."

For more see Development of a Magnetic-Bearing Momentum Wheel for the
AMSAT Phase 3-D Small Satellite by Michael SCHARFE (DK7UX)*, Karl
MEINZER (DJ4ZC)*, Ralf ZIMMERMANN (DL1FDT)** at:
http://www.amsat.org/amsat/sats/phase3d/wheels/index.html

Rick
W2GPS


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