From:
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The ARRL Letter
Vol. 19, No. 50
December 29, 2000
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==>RESET RESTORES AO-40 TRANSMISSION
Merry Christmas, AMSAT--AO-40 is back! Following a 12-day silence, AO-40
once again is transmitting telemetry. In response to an L-band command sent
Christmas Day by command station ZL1AOX, AO-40 resumed transmitting on 2.4
GHz. Software was reloaded to permit telemetry transmissions on 2401.305
MHz. Some problems remain on the satellite, however.
"Recovery of AO-40 continues, and some housekeeping tasks were performed by
the command stations to improve and stabilize the situation," said Peter
Guelzow, DB2OS, of the AO-40 team. Guelzow says new software routines were
loaded successfully to restore the battery-charge regulator system and other
housekeeping functions. "We will now start a detailed analysis of the
situation," he said.
Telemetry transmissions from AO-40 ceased December 13 while ground
controllers were testing the onboard 400-Newton propulsion system following
an initial orbital shift. Some observers feared the satellite had been
irreparably damaged. Guelzow says ground stations now have regained control
of the satellite. Ground controllers hope the telemetry might yield some
clues about what went wrong aboard the satellite to make it stop
transmitting.
After onboard software watchdog routines failed to restart beacon
transmissions automatically, a full reset command and an initialization
block to switch on the S2 S-band transmitter were sent via L-band.
Guelzow said telemetry revealed that some temperature sensors have failed
and some current sensors indicated incorrect values, but solar sensors
seemed to be working fine. The good news was that AO-40's power
situation--in particular the battery voltages--looks nominal.
Guelzow said additional software would be loaded in the next few days and
the various uplinks checked out before any attempts are made to turn the
2-meter transmitter back on. "Clearly, we need more time to analyze and
understand what has happened here," Guelzow said. He said that while there
are no indications that the 2-meter beacon transmitter has failed, ground
controllers don't want to risk losing communication again. "So for the next
days the spacecraft will continue to be transmitting on S-Band only," he
said.
Phase 3D Project Leader Karl Meinzer, DJ4ZC said AO-40 command stations
"will continue to follow a conservative philosophy" with a primary goal of
not causing additional damage while retaining as much evidence as possible
to analyze what made the beacon transmissions stop.
On December 22, AMSAT proposed holding an inquiry into the incident that led
to the loss of communication with AO-40. A letter from AMSAT-NA President
Robin Haighton, VE3FRH, said "AMSAT believes that it is in the best
interests of our organization to determine all the facts surrounding this
incident and to make sure that a similar situation cannot happen again
either on AO-40 or on a future satellite."