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NEWINGTON, CT, Jan 27, 2004--The AO-40 satellite could be in serious trouble. According to AO-40 ground controllers, telemetry from the satellite indicated a substantial drop in voltage on the operating bus at around 0100 UTC today, and the bird went silent.
"AO-40 is in a very critical situation at the moment," reported AMSAT-DL (Germany) President Peter Gülzow, DB2OS, in a posting to the AMSAT bulletin board. "Our command team is working hard to get AO-40 fully back under control."
Ground controllers say that AO-40's battery voltage dropped suddenly on Orbit 1488 from 26 V to 14 V, although low-voltage anomalies already had been noted the past few days. "We currently believe that, in some kind of domino effect, more battery cells shorted," Gülzow said. A unconfirmed report said there was a rise in the satellite's heat pipe temperature--from 27 degrees Celsius to 92 degrees Celsius--just before the voltage dropped.
Several stations reported that around the time of the voltage drop, the satellite's S-band (2.4 GHz) signal dropped rapidly. "This would be consistent with the low bus voltage, preventing the S-TX from working properly," Gülzow said. "At the moment we assume that the IHU is still working."
The "IHU" is AO-40's "internal housekeeping unit"--a computerized control system. The AO-40 command team has been investigating the earlier low-voltage anomaly over the past few days to determine if the main battery may have developed a shorted cell or if another problem was to blame.
Command stations have been sending blind commands to the spacecraft in an attempt to get AO-40 to switch over to its auxiliary battery. Gülzow says if that doesn't work, then the IHU will be reset and software to switch the relays will be uploaded.
Gülzow said the delicate operations may take some time and may require a better sun angle on the spacecraft before they're successful.
Ground controller Stacey Mills, W4SM, reported that the "extreme low voltage event" shut down the satellite's S-band transmitter and "probably" crashed the IHU-1. In a posting today on the AMSAT-DL Web site, he indicated that the main and auxiliary batteries had been tied together and "should be charging." He said the command team would be waiting with "fingers crossed" until the next orbit to see if the voltage on the batteries comes up to normal levels and the IHU-1 could be rebooted and reloaded.
The AO-40 satellite was the result of AMSAT's ambitious international Phase 3D project. Launched in November 2000, the satellite suddenly went dark the following month as ground controllers were testing the onboard 400-newton propulsion system that was to place the spacecraft into its planned orbit.
While some systems were irreparably damaged, ground controllers were able to get AO-40 partially up and running again, and the satellite's transponders have been in active use since May of 2001. It was subsequently determined that an anomaly involving a fuel valve had caused an onboard explosion.
AO-40 had been operating with 435 MHz and 1.2 GHz uplinks and a 2.4 GHz downlink and beacon.
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