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ARRL Satellite Bulletin ARLS016 (2001)

ARLS016 AO-40 Attitude Control System Appears Functional

QST de W1AW  
Space Bulletin 016  ARLS016
From ARRL Headquarters  
Newington, CT  August 17, 2001
To all radio amateurs

ARLS016 AO-40 Attitude Control System Appears Functional

The commissioning of the AO-40 satellite took another giant step
forward this week as ground controllers reported success in testing
the spacecraft's attitude control system--the momentum wheels. AO-40
controllers hope to use the momentum--or ''reaction''--wheels to aim
the satellite's antennas and, eventually, its solar panels. The
testing paves the way for possible deployment of the solar array and
better signals on the ground.

''We can say with some caution that we have a working three-axis
control system!!!'' enthused AMSAT-DL President and AO-40 team
member Peter Guelzow, DB2OS, in a posting to the AMSAT bulletin
board.  Until now, AO-40's attitude has been under ''spin control.''

The three-axis control offered by the momentum wheels will mean much
more positive attitude control from the ground anywhere in the
satellite's orbit.

After preliminary tests to energize the momentum wheels earlier this
week, ground controllers Stacey Mills, W4SM, and James Miller,
G3RUH, ran them up to more than 100 RPM Aug 16 during orbit 365 and
left them at this speed for about a half-hour. Telemetry before and
after the spin-up, once the solar sensors re-locked, showed that the
system appeared to be working properly. The momentum wheels are
designed to run at a nominal operating speed of 1000 RPM.

''More tests will be done over the next few weeks, before we will
transfer the spacecraft from spin stabilization into three-axis
stabilization,'' Guelzow said.


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