NEWINGTON, CT, Apr 26, 2001--AMSAT-NA President Robin Haighton, VE3FRH, this week raised the possibility that AO-40 could inaugurate transponder operation this summer, if tests and orbital maneuvers between now and then go as planned.
"We are learning how to fly this thing," Haighton said. "But I still think we're going to end up with a darned good satellite."
The most likely initial transponder configurations would be Mode L/S--1.2 GHz up and 2.4 GHz down, Mode U/S--435 MHz up and 2.4 GHz down, and possibly Mode V/S--145 MHz up and 2.4 GHz down. "It looks like a good bet," Haighton said of the probability that the three modes would prove useful from the damaged satellite. He predicted that Mode U/S operation from AO-40 would surpass what had been available a few years ago from the now-defunct AO-13. "We have estimated that the downlink could provide up to 27 dB more signal."
Recent data from the spacecraft suggest that the mid-December incident that silenced AO-40 for two weeks and rendered some systems unusable also might have blown a hole in the bottom or Z axis of the spacecraft. "Speculation is there could be damage, and sunlight is getting right in," Haighton said, noting that ground controllers have detected a distinct rise in temperature when sunlight strikes that side of the satellite. That theory would go along with the loss of the satellite's omnidirectional antennas, Haighton added. The speculated opening was not causing any major problems, he said, but it could explain why efforts to adjust AO-40's attitude via magnetorquing have been unpredictable.
As the AO-40 recovery effort continues, Haighton said, ground controllers plan to raise the height of the perigee in the very near future. That process, using the onboard arc-jet motor, could take up to several weeks. The AO-40 team hopes the maneuver will minimize or eliminate possible effects on the satellite's orbit caused by atmospheric expansion at the peak of the solar cycle.
AO-40 currently is approximately 320 km--almost 200 miles--above Earth at perigee--its closest point--and some 51,000 km--some 31,600 miles--at apogee. Plans call for raising the orbit at perigee to around 520 km, or some 320 miles. The maneuver would "hardly affect" the satellite's apogee, Haighton said. The arc-jet would be operated without electrically igniting it--using the pressure of the ammonia fuel alone. This would yield about half the normal thrust, Haighton said.
Once the orbit has been adjusted, ground controllers would orient the spacecraft's attitude and check out the various onboard transmitter and receiver systems to see what works and what does not. "We're still pretty confident that the 2 meter and 70 cm transmitters are not there," Haighton said, "but we're equally confident that the receivers for those bands still are."
The satellite has been transmitting telemetry on the 2.4 GHz (S-2) beacon, and signals reportedly have continued to improve--although the beacon has been out from time to time as needed to conserve power during eclipse periods. Ground controllers recently commanded the YACE camera to take several pictures, starting with orbit 216, and 11 images were downloaded. "The pictures show the characteristic rings and blisters that have been detected on the YACE photographs since the December 13 incident (damage to the lens from fuel residue?)," said a posting on the AMSAT-DL Web site. A prevailing theory about the image degradation was that the camera may have been damaged by direct sunlight into its lens, but James Miller, G3RUH, in an analysis subtitled "Did the Cameras Fry?" has disputed that notion.
Full deployment of the spacecraft's solar panels is "still several months away," Haighton said. Also uncertain was the satellite's ultimate inclination with respect to the equator. It was planned for AO-40 to have a 60-degree inclination, but given the satellite's compromised circumstances, "we'll be lucky if we can get 10 or 15 degrees," Haighton said. The current inclination is six degrees.
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