ARLA/CLUSTER: Alguém escutou o OSCAR-11...?

[João Gonçalves Costa]

OSCAR-11 Update - reception reports requested

In his report dated 20 December Clive G3CWV makes a special request for any reception reports of OSCAR-11 which was launched in 1984.

During the period 15 November to 19 December 2007 no signals have been received from the satellite. No reports of reception have been received.

Eclipses have continued and are expected until mid January 2008. Although the maximum duration of the current eclipses is less than those earlier this year, it is doubtful whether the satellite will be heard for any sustained period. While in continuous sunlight during September and October the satellite was unable to support continuous operation.

It is likely than the satellite will only be heard by chance, by stations listening for other satellites on 145.826 MHz.

The current status of the satellite, is that all the analogue telemetry channels, 0 to 59 are zero, i.e they have failed. The status channels 60 to 67 are still working. The real time clock is showing a large accumulated error, although over short periods timekeeping is accurate to a few seconds per month. The day of the month has a bit stuck at 'one' so the day of the month may show an error of +40 days for some dates. The time display has switched into 12 hour mode. Unfortunately, there is no AM/PM indicator, since the time display format was designed for 24 hour mode. More data is required to determine exactly when the date changes.

The spacecraft computer and active attitude control system have switched OFF, i.e. 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 23 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. The ON/OFF times have tended to be very consistent. The average of many observations show this to be 20.7 days, i.e. 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. If you need to know what OSCAR-11 should sound like, there is a short audio clip for you to hear. There is an example of the latest telemetry received from the satellite. The website 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 http://www.users.zetnet.co.uk/clivew/

Please send reception reports to xxxxx  amsat.org (please replace xxxxx by g3cwv) or post to amsat-bb. If you are able to record the satellite as a WAV file, please do so, but let me know what you have, before sending it !

If you need to hear what the satellite sounds like, please visit my website http://www.users.zetnet.co.uk/clivew
The satellite transmits on 145.826 MHz. Set receiver to NBFM.


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



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