AO-40 Gives Earthlings Another Scare

From the ARRL...


NEWINGTON, CT, Aug 28, 2001--Sighs of relief were heard around the world as the S2 beacon aboard the AO-40 satellite reappeared August 28 after an ominous absence. The beacon failed to return on Orbit 381 at MA=44 (MA, mean anomaly, an orbital position), when the RUDAK connections shut off as programmed.




Gunter Wertich, DF4PV, who is equipped for moonbounce work, reported hearing normal telemetry blocks very weakly, however, so ground controllers were assured that the onboard computer had not crashed. "It was suspected that the solid-state matrix IF connections had not latched properly during the switch-over at MA=44," said ground controller Stacey Mills, W4SM. "In that case, Gunter would have been hearing 'bleed through' of the middle beacon through the IF matrix."



Mills said that when the satellite came into view at his Virginia location, the middle beacon-to-S2 transmitter connection was manually cycled off and on, "and the middle beacon popped back up."



The RUDAK has been turned off temporarily, Mills said, but the schedule will remain in place. For now, there will be no middle beacon and no RUDAK from MA=30 to 44. The middle beacon is off from MA=220-250 because of eclipses.



According to Mills, the beacon glitch has occurred at least once before--both times soon after the December incident--and may be related to critical timing issues in the MUX output to the IF matrix. "This event will be studied further, and we will watch closely for several days to see if this occurs again," he said. "If so, the fix may be to simply add additional timing delays to the automated matrix switching software."



In the December "incident," AO-40 went silent for nearly two weeks following an onboard explosion that damaged or compromised some of the spacecraft's equipment and experiments. Ground controllers were able to revive the satellite on Christmas Day. Transponders were put into operation last spring.