ARRL

ARRL Satellite Bulletin ARLS003 (2004)

SB SPACE @ ARL $ARLS003
ARLS003 AO-40 Command Team Plays Waiting Game

ZCZC AS03  
QST de W1AW  
Space Bulletin 003  ARLS003
From ARRL Headquarters  
Newington, CT  February 4, 2004
To all radio amateurs

SB SPACE ARL ARLS003
ARLS003 AO-40 Command Team Plays Waiting Game

Ground controllers for the now-dark AO-40 satellite are waiting for
something to break aboard the spacecraft. Specifically, they want
one of the cells of the main battery bank to open up and "unshort"
the power bus. That open circuit then could mean the command team
would be able use the auxiliary batteries--now tied in parallel with
the main battery bank--to restart the satellite. The command team
hypothesizes that a failure within the main battery is clamping the
bus voltage low. The command team meanwhile continues to signal the
satellite to turn off the main batteries and turn on the auxiliary
batteries and the 2.4 GHz "S2" downlink transmitter.

"If we have approximately 10 V on the main bus, then these commands
should be making it through," said ground controller Stacey Mills,
W4SM, "but the S2 transmitter was not designed to run below 20 V and
is not coming on."

AO-40 has been silent since January 27 (UTC), in the wake of a
precipitous voltage drop. The satellite's controllers believe that
one or more shorted battery cells are at the root of the problem.

Mills said the AO-40 command team assumes the bus voltage aboard
AO-40 is lower than 12 V, and that the onboard IHU-1 ("internal
housekeeping unit") computer, the command receivers or the battery
changeover relay have insufficient power to operate.

There's some conjecture that the current problem may be related to
the near-catastrophic incident that occurred onboard AO-40 in
December 2000 less than a month after its launch during testing of
the 400-newton propulsion system. That mishap destroyed some of the
spacecraft's functionality and may have caused other damage that's
only now coming to light. Following the 2000 incident, the AO-40
command team was able to restore some of the satellite's
functionality.

Updates on the AO-40 situation are being posted on the AMSAT-DL Web
site at http://www.amsat-dl.org/journal/adlj-p3d.htm#NEWS.  There's
additional information on AO-40 on the AMSAT-NA Web site,
http://www.amsat.org/.
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