Momentum Wheel with Magnetic Bearing 
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Attitude Control of the AMSAT AO-40 Spacecraft 


Most satellites today use momentum wheels for attitude control. This way
the antennas and the solar generator can always be pointed into the
right direction. 

Conventional momentum wheels with ball bearings frequently caused
problems since in the vacuum of space the lubrication of the bearings is
very difficult. 

For more than 20 years it has been proposed to use magnetic bearings
working with no physical contact and thus no wear. 

The development of such systems turned out to be rather difficult. For
space applications bearings with two active controlled axes and one
passive axis had not been developed to the point which allowed them to
be tested in space . 

Now such a system is under testing on the AMSAT OSCAR 40 satellite
and developed for by AMSAT-DL's Prof. Dr. Karl Meinzer (DJ4ZC) from 
the University of Marburg in cooperation with the TH Darmstadt. 
It is hoped that this generally makes available a technology which 
will improve the reliability of future 3-axis-controlled spacecraft. 

Furthermore it is hoped that the experience gained with magnetic
levitation systems will find applications in other areas, for instance
for magnetic levitation trains and in large size electromechanical
projection display systems. 

More links:

http://www.amsat-dl.org/momentum.html
http://www.amsat-dl.org/journal/artikel/adlj-rad.htm

http://www.amsat.org/amsat/sats/phase3d/wheels/index.html
http://www.amsat.org/amsat/sats/phase3d/wheels.html