AO-40 Makes Move to Higher Orbit
NEWINGTON, CT, Dec 13, 2000--AMSAT News Service reports that ground controllers this week moved the AO-40 Amateur Radio satellite into a higher orbit, but not without a hitch. During an initial pre-programmed "burn" attempt using the satellite's onboard 400-Newton motor on Sunday, AO-40's perigee came and went and the burn did not take place.
"The stored telemetry was analyzed, and we learned that the sequencer went through all the necessary steps but there was no helium pressure and consequently no engine burn," said the latest AMSAT bulletin from AO-40 Project Leader Karl Meinzer, DJ4ZC, and AMSAT President Robin Haighton, VE3FRH. Helium pressure is needed to open the fuel valves. A similar valve problem also occurred during the test phase of Phase 3D; that failure was attributed to aging of components.
By cycling the valve on and off several times, engineers eventually were able to build up enough helium pressure to activate the fuel valve and accomplish the burn on Monday. The burn lasted three minutes longer than planned, however, sending AO-40 into a 60,000 km (37,200 mile) apogee rather than the planned 50,000 km (31,000 miles). Ground controllers say the added altitude may work to their advantage by easing the demands of the electric "arc jet" propulsion system that will be used to "fine tune" the satellite's final perigee.
Questions remain as to whether any damage could have been done to the 400-Newton motor because of the ad hoc method use to achieve proper operating pressure for the fuel valves. AMSAT says a step-by-step analysis is under way. "During the next few days we will investigate this matter in detail," the AMSAT update bulletin said. "If we have a real problem with the 400-N propulsion system, we may need to change our strategy for achieving a useful final orbit."
No attitude or altitude changes are planned for the next few days, and attention will be focused on correcting problems with the 70-cm transmitter aboard AO-40. "During these tests, we will find out if we can operationally plan on using the 70-cm transmitter or not," the AMSAT statement said. Following launch and separation, ground stations were unable to receive the 70-cm beacon signal. The beacon was subsequently moved to 2 meters.
Ground controllers also are looking into problems with the Internal Housekeeping Unit-2 (IHU-2) computer system, which has suffered occasional crashes apparently related to radiation encountered on orbit. Current plans call for installing additional software in the IHU-2 to minimize the problem. "Until that time, we will have to live with IHU-2 crashes, which seem to be caused by hard radiation and typically occur when the satellite comes out of perigee and again enters the radiation belts," the AMSAT statement said.
An image of Earth taken by the YACE camera on board AO-40. |
The RUDAK digital communications processor aboard AO-40 was fired up for the first time over the weekend. Jim White, WD0E, reports the RUDAK team in Colorado was able to command the AO-40 to raise the level of one of the RUDAK 9.6 k modulators. Following the first motor burn and resulting orbit change, RUDAK and the S2 (2.4 GHz) transmitter were shut down to conserve power until the orbit, orientation, and power budget are again suitable for working with RUDAK.
The next-generation Amateur Radio satellite formerly known as Phase 3D was launched in mid-November. For more information on AO-40, visit the AMSAT-NA Web site. Additional information is available at http://ao40.homestead.com.
Page last modified: 03:26 PM, 13 Dec 2000 ET
Page author: awextra@arrl.org
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