From: *************** The ARRL Letter Vol. 19, No. 50 December 29, 2000 ***************

==>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."