OSCAR-11 REPORT

19 August 2006

OSCAR-11 IS BACK! During the period 17 July to 19 August 2006 the satellite was heard on 26 July for a few orbits, and then from 16 August. At the time of writing it is currently transmitting.

Observation of the 145.826 MHz. beacon transmission times, indicate that the watchdog timer has timed out for five periods of 20.5 days during the eclipse season. The eclipses have now ended, and the satellite should be in continuous sunlight until next year. If the normal watchdog timer sequence continues, the beacon should switch OFF around 26 August, and restart around 06 September.

On 26 July real time clock showed an error of 64.5 days, an increase of 41.7 days since it was last heard on 05 May. The clock is now showing further problems, the date is now 53 July, but is still incrementing. The hours are showing an erratic behaviour.

I am indebted to Peter ZL3TC, Dave G1OCN, and Dave WB6LLO for their reports and for monitoring the satellite, during this period. Many thanks.

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.

The watchdog timer now operates on a 20 day cycle. During the three months before May (when the eclipses started), the ON/OFF times were 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, poor solar attitude may result may result in a low 14 volt line supply, which may cause the beacon to switch OFF prematurely, and reset the watchdog timer cycle. When this occurs, the beacon is OFF for 20.7 days.

The Beacon frequencies are -

VHF 145.826 MHz. AFSK FM ASCII Telemetry

UHF 435.025 MHz. OFF

S-band 2401.5 MHz. OFF

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 www.users.zetnet.co.uk/clivew/

If you place this bulletin on a terrestrial packet network, please use the bulletin identifier $BID:U2RPT124.CWV, to prevent duplication.

73 Clive G3CWV xxxxx@amsat.org (please replace xxxxx by g3cwv)