[amsat-bb] AO-40: Momentum Wheels tested!!!

[Peter Guelzow <peter.guelzow@xxxxxxxxxxxx>]

AO-40: Momentum Wheels tested!!! 

Dear All, 

In Orbit #364 the wheels were powered up and synched at 0 RPM
immediately!! Power drain was not detectable. No attempt was yet made in
this test to spin up the wheels to 100 RPM. This will be saved for the
next orbit. 

In fact, running the test at 0 RPM was already the most critical test.
If the wheels could not "fly" and move freely, there would never be any
"sync" detection in the telemetry.. 

As a next step, the wheels would be programmed to say 100 rpm rotation
(all in the same direction and at the same time) and than again we wait
for synch, which should be there in the order of a minute. If everything
goes well, then we let them run for a while to allow spin measurement of
the s/c and observing power consumption. 

This test would give us the most important calibration constant of the
wheel system, namely the ratio of s/c MOI and to the MOI of the wheels.
In fact, since the wheel MOIs are exactly known, this means that we
would be able to determine s/c MOI to about 5% - from this we could
possibly infer how much fuel is left in the N2O4/MMH tanks. Also this
figure is needed for the 3-axis software and for planning the
spin/3-axis transition. 

Congratulations to Karl, Stacey, James and all involved!!!!


Here some more general information's:


Momentum Wheel with Magnetic Bearing 
------------------------------------
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


73s Peter DB2OS
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