Ground controllers for the AO-40 satellite are trying to figure out just what happened to cause a significant drop in the spacecraft’s bus voltage, taking it off the air. The satellite remains silent in the wake of a precipitous voltage drop from around 26 volts down to 18 volts early on January 27 (UTC). AO-40 controllers are fairly certain that one or more shorted battery cells are at the root of the problem. Efforts to restart the satellite’s 2.4-GHz downlink transmitter have been unsuccessful.
“Our current best understanding is that we suffered a catastrophic failure of the main battery, which is clamping the bus voltage at a low level,” Stacey Mills, W4SM, of the AO-40 command team said in a posting on the AMSAT-DL Web site.
The AO-40 satellite was the result of AMSAT’s ambitious international Phase 3D project. The AMSAT-NA Board of Directors met January 29 to review the current situation. “The next few weeks will be of great interest as the satellite is entering into a sun angle which is becoming increasingly favorable for charging the batteries,” said AMSAT-NA President Robin Haighton, VE3FRH. Tests are under way on spare batteries in AMSAT’s Orlando, Florida, lab in an effort to simulate the failure mode and determine what might be done to recover the satellite.
“At this time, AMSAT engineers and scientists are optimistic about the chances of recovering but–like the NASA Spirit problem–this may take some time to accomplish,” Haighton said.
The AO-40 ground team has been sending blind commands to the spacecraft to activate its onboard computerized control system in order to switch in the auxiliary battery bank, which was tied to the main battery bank after a bus voltage drop January 26, and disconnect the main battery.
Mills said that while ground controllers don’t claim to fully understand what happened aboard AO-40, operator practices were not to blame. “AO-40 was designed to withstand all that you can throw at it,” he said.
Mills explained that the main AO-40 batteries consist of 20 40-Ah cells arranged on three of the radial support arms inside the spacecraft–two packs of seven cells and one pack of six cells.
“It is entirely possible or even probable that the main batteries suffered some damage during the 400-N motor event,” Mills said, referring to the onboard catastrophic incident that caused AO-40 to go dark less than a month after its November 2000 launch.
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 2001. It was subsequently determined that an anomaly involving a fuel valve essentially 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.
“If it’s at all possible to bring AO-40 back, we will,” said Mills, who concedes that he’s “lived and breathed AO-40” for more than four years. “No success for even weeks or months does not mean that we won’t eventually be successful. We will sure keep trying.”