A weak “noise” on the AO-40 2.4-GHz beacon frequency has raised hopes that AO-40 may still be alive. 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.
Colin Hurst, VK5HI, of the AO-40 command team reports that on March 9 between 0310 and 0320 UTC (orbit 1541) he “noted a noise peak of 4 to 5 dB” in the vicinity of the expected beacon frequency after he’d issued a transmitter reset command sequence to the satellite. “The width of this peak was about 5 kHz,” he said. After listening for about 15 seconds, he issued a command to shut down the transmitter, and the noise peak disappeared.
Hurst said he also transmitted several commands involving the auxiliary batteries but did not attempt to turn the beacon on again. “This tends to suggest that the IHU [Internal Housekeeping Unit computer] and L Band [1.2 GHz] receiver are operational,” he said.
The AO-40 command team theorizes that a cell in the main battery pack has shorted, clamping the bus voltage below the point where it can operate the satellite. The spacecraft’s auxiliary batteries are believed to be in parallel with the main batteries, and commands sent so to swap to the auxiliary batteries have been unsuccessful. AO-40 Earth stations are continuing to send commands to the satellite in order to switch the batteries.
Updates on AO-40 are available on the AMSAT-DL Web site,
http://www.amsat-dl.org/journal/adlj-p3d.htm