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ARRL Satellite Bulletin ARLS006 (2001)

ARLS006 AO-40 Spinup Under Way

QST de W1AW  
Space Bulletin 006  ARLS006
From ARRL Headquarters  
Newington, CT  April 4, 2001
To all radio amateurs

ARLS006 AO-40 Spinup Under Way

While using the onboard magnetorquing system to adjust AO-40's
attitude, AO-40 ground controllers were able to bring the spin rate
from nearly 18 RPM down to 1.8 RPM--the planned final value. Now,
they're planning to raise the spin rate to 5 RPM to check excessive
attitude change.

Citing what he called ''some confusing results,'' AMSAT-DL President
and key AO-40 project team member Peter Guelzow, DB2OS, said AO-40's
attitude had changed faster than the experts believed possible.

Ground controllers theorized that the effects of drag at perigee
were much higher than anticipated. The extra drag at perigee might
have been caused by Earth's atmosphere ballooning outward in
response to solar activity. As a result, it was decided to spin up
the spacecraft to compensate for the too-rapid changes in attitude
due to drag.

''This will give us additional breathing space,'' Guelzow said. Ground
controllers have commenced a five-perigee magnetorquing sequence to
raise the spin rate to 5 RPM. ''In addition,'' Guelzow said,
''preparations to test the arcjet thruster, as soon as accurate
attitude is determined, are under way.''

Further plans for orbit correction and commissioning of AO-40 will
depend on how the arcjet tests go. If the arcjet tests are
satisfactory, initial transponder operation could be attempted
before summer.

AO-40's telemetry data stream halted briefly late last week.
''Because of the recent very high solar activity, the AO-40 team at
first thought that the IHU-1 had crashed,'' Guelzow said. It was
later determined that a soft error had occurred and was corrected by
the onboard EDAC, or Error Detection and Correction unit.


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