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www.southgatearc.org
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OSCAR-11 Report 18 July 2006RECEPTION REPORTS REQUESTED! Due to solar eclipses (see below) the VHF beacon on 145.826 MHz. may only transmit for a short time, perhaps for only a few orbits, or even less, at irregular intervals. Any reception reports would be appreciated. Please e-mail xxxxx@amsat.org
(replace xxxxx by g3cwv), or post to AMSAT-BB. If you are unfamiliar with
the sound of OSCAR-11, there is an audio clip on my website During the period 15 June to 17 July 2006 nothing has been heard from the satellite. It was last heard on 05 May, just one day before the solar eclipses were due to start. These eclipses will continue until 04 August 2006, reaching a maximum duration of 22% around 19 June. If the satellite behaves in the same way as it did last year, regular 10 day transmissions should re-start, sometime in August. Once again I am indebted to Jeff KB2M, for monitoring the satellite, during this period. He has not heard any signals. The current status of the satellite is that all the analogue telemetry channels, 0 to 59 are zero, ie they have failed. The status channels 60 to 67 are still working. The spacecraft computer and active attitude control system have switched OFF, ie. the satellite' attitude is controlled only by the passive gravity boom gradient, and the satellite is free to spin at any speed. When telemetry was last received it showed that one of the solar arrays had failed, and there was a large unexplained current drain on the main 14 volt bus. After 22 years in orbit the battery has undergone around 100,000 partial charge / discharge cycles, and observations suggest that it cannot power the satellite during eclipses, or sometimes during periods of poor solar attitude. When last heard, the on-board clock showed a very large accumulated error. On 05 May it was 22.76456 days slow. The clock lost two hours during the last OFF period, and nine hours during the last transmission period. The observations of clock errors suggest that the clock may slow or stop when the battery voltage is low. The watchdog timer now operates on a 20 day cycle. During the three
months before the eclipses started, the ON/OFF times have been very consistent,
and the average of many observations show this to be 20.7 days, ie. 10.3
days ON followed by 10.4 days OFF. However, during the present solar eclipse
season, power supply problems, may result in a low 14 volt line supply,
which may cause the beacon to switch OFF prematurely, and reset the watchdog
timer cycle. Listeners to OSCAR-11 may be interested in visiting my website which contains an archive of news & telemetry data. It also contains details about using a soundcard or hardware demodulators for data capture. There is software for capturing data, and decoding ASCII telemetry. The
URL is
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