[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                    OSCAR-11 REPORT

                   20 November 2006


During the period 30 October to 20 November, the satellite was heard
from 07 to 17 November. Good signals steady signals have beeen heard on all
passes, and excellent copy of telemetry obtained.

The date/time stamp has been of interest.  Since the satellite was heard on
18 October the on-board clock has maintained accurate time, to within two
seconds over a period of 30 days. This compares with the average
gain of five seconds per month, recorded when the satellite was fully
operational.

The date counter appears to be incrementing correctly, but the day of the
month is not reset to one, at the end of each month, and is not
incrementing the month counter correctly. During the OFF period the month
counter changed from '0=' to '10'. On 17 November the date was shown as 51
October. However, the day of the week counter appears to be incrementing
correctly.

If the satellite watchdog timer continues to operate normally, the
beacon should switch ON
around 29 November. If the satellite is not heard around this time, it may
be worth listening around 09 December.

I am indebted to Peter ZL3TC, for his reports, which helped me determine
when the satellite last switched ON. 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 were 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. The ON/OFF times have
tended to be very consistent. 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. If you need
to know what OSCAR-11 should sound like, there is a short audio clip for
you to hear. 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 www.users.zetnet.co.uk/clivew/

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT127.CWV, to prevent duplication.

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