AMSAT: OSCAR-11 Report
20 November 2006
During the period 30 October to 20 November, the satellite was heard
from 07 to 17 November. Good, steady signals have been 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 http://www.users.zetnet.co.uk/clivew/
73 Clive G3CWV
xxxxx@amsat.org (please replace xxxxx by g3cwv)
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