Amsat Oscar-11 report
During the period 20 October to 21 November 2005 the VHF beacon
on 145.826 MHz. resumed transmissions on 21 October, and continued
until 30 October.
Transmissions then resumed, as expected, on 10 November. However,
the beacon stopped transmitting prematurely, sometime between 14
and 16 November. If the watchdog resets as expected, then the beacon
should restart around 06 December.
Signals have been very variable during this period. Sometimes received
at good strength, at other times they were inaudible, even with
the BFO switched ON (ie. in CW mode).
The on-board clock continues to show a very large error. Currently
it is 19.9 days slow. All the analogue telemetry channels, 0 to
59 are zero, ie they have failed. The status channels 60 to 67 are
still working.
The eclipses have now ended, and the satellite should be in continuous
sunlight for the remainder of this year, and next year until early
May. This should help the satellite to continue transmitting, although
continuous sunlight can cause problems due to excessive temperatures.
Power supply problems can be caused by poor earth pointing attitude,
ie: the sunlight illuminating the ends of the satellite, instead
of the solar arrays.
The watchdog timer appears to be operating on the 20 day cycle,
ie: approximately ten days ON followed by 10 days OFF. It appears
to be unaffected by problems of the on-board clock. However, poor
solar attitude, and battery problems, may be combining to produce
a low 14 volt line supply. This appears to be causing the beacon
to switch OFF prematurely, and resets the watchdog timer cycle.
It seems very likely that the battery is now unable to retain its
charge, due to having endured around 100,000 partial charge/discharge
cycles, always a problem with NiCad cells. When analogue telemetry
was transmitted, it showed an unexplained current drain from the
14 volt line. This just adds to the present problems.
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 http://www.users.zetnet.co.uk/clivew/
73 Clive G3CWV g3cwv@<no spam>amsat.org
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