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from the arrl letter about ao-40

The ARRL Letter
Vol. 20, No. 47
November 30, 2001


Necessary adjustments to AO-40's attitude to compensate for unfavorable
sun angles over the next several months will silence the satellite's
transponders for a while. Recent reports indicate that AO-40 continues to
operate well, providing coverage between many parts of the world.

Command station team member Stacey Mills, W4SM, says, however, that he's
puzzled and disappointed by the relatively low numbers of users on AO-40
during the last month or so. "I'm not sure why," he told ARRL this week.
"This is prime time, and we won't have such good conditions much longer
until the three-month 'bad angle' cycle passes."

A scheduled attitude shift to compensate for the unfavorable sun angle
will leave AO-40's antennas pointing away from Earth until next spring and
lead to a transponder shutdown period that could start as soon as late
December. The satellite is currently in a long period during which Earth
eclipses the sun near perigee--its point closest to Earth. AO-40 relies on
solar panels for its power.

Mills said that testing and development continue on AO-40's three-axis
control system, but three-axis control would not be ready in time to avoid
the unfavorable solar-angle season. AO-40 will remain in spin mode for at
least a few more months, he said. 

Mills estimated that ground controllers may need to start shifting the
satellite's attitude starting sometime just before Christmas. He didn't
expect a favorable sun angle that would again allow pointing AO-40
directly toward Earth (ALON/ALAT 0/0) until mid-April. "It's possible that
we can leave the transponders on during the first part of the move and
turn them back on slightly before April 15 as we start back toward 0/0,"
Mills said, "but you can figure that things will be sub-optimal from about
Christmas until April 15."

Mills said earlier this month that ground controllers now assume that
AO-40's S1 transmitter is beyond recovery. The S1 transmitter quit
abruptly in August, but before going down, it had produced excellent
results. Ground controllers also have done additional testing on the
2-meter (V band) transmitter, which, Mills conceded, also appears lost.

The next-generation AO-40 satellite marked its first year in orbit during
November. The former "Phase 3D" satellite was launched November 16, 2000,
aboard an Ariane 5 launcher from the European Spaceport in Kourou, French
Guiana. Transponder operation began May 5, 2001. AO-40 is the largest
Amateur Radio satellite ever put into space. 

The current AO-40 transponder operating schedule and more information are
available via the AMSAT Web site <http://www.amsat.org>.

Bruce Paige, KK5DO                                      Internet: kk5do@arrl.net 
Houston, Texas                                                         kk5do@amsat.org 
AMSAT Awards Manager                                kk5do@amsatnet.com
ARRL Awards Manager (WAS, 5BWAS, VUCC), VE                     
Houston AMSAT Net - Tuesday, 8PM CST on W0KIE GE-7, T5, 
Also available on Real Audio at http://www.amsatnet.com                
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