AO-40 Achieves a New Orbit

From the ARRL...


NEWINGTON, CT, Jul 5, 2001--AO-40 now is in a new orbit. Recent efforts to raise the satellite's orbit at perigee--its point closest to Earth--were somewhat more successful than originally anticipated. Ground controllers had planned to lift the perigee from 280 km to around 500 km. Successive firings of cold arcjet ammonia fuel resulted in an orbit that's 851 km at perigee, however.




"Indeed, the good news is that AO-40 is now in a safe and stable orbit!" said AMSAT-DL President Peter Guelzow, DB2OS, on behalf of the AO-40 team. "The bad news: All 53 kg of ammonia probably has been used up." This means further orbital adjustments--at least using the arcjet--are unlikely. Guelzow said ammonia stopped flowing after orbit 302, "and the pressure indicators in the telemetry show no more pressure in the motor and in the ammonia tanks, while the perigee clearly is higher than anticipated."



AO-40's height at apogee--58,971 km--was unchanged by the orbital adjustment.



Guelzow said stored telemetry was being downloaded and analyzed. Shut down prior to the start of the orbital adjustment, AO-40's transponders remain off the air. They will stay off as ground controllers adjust the satellite's attitude using on-board magnetorquing. The spacecraft's attitude will be moved back to ALON/ALAT 0/0 as soon as possible and command stations currently are preparing for magnetorquing, Guelzow said.



AMSAT-NA President Robin Haighton, VE3FRH, has said it's hoped that a slightly higher perigee for AO-40 will eliminate the effects of what he described as "a mysterious force" that alters the satellite's attitude when it comes through perigee. One theory, he said, is that atmospheric expansion caused by the current sunspot cycle peak was influencing the satellite's orbit in some way. The higher perigee should eliminate any atmospheric impact.