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OSCAR-11 Report



                  OSCAR-11 REPORT

                  18 April 2005

During the period 10 March to 18 April 2005 reliable signals have been
received from the 145.826 MHz. beacon, transmitting continuous ASCII
telemetry from 18 March to 27 March and from 07 April to 17 April.  At
times signals have been weaker than usual, and subject to local
interference (QRN), which has been stronger than usual.

The beacon operates under control of the watchdog timer. Observations have
indicated that the cycle is approximately 10.3 days ON followed by 10.4
days OFF. Assuming that this cycle continues, the beacon should switch ON
around 27/28 April.

When the beacon resumed its transmissions on 07 April, the time stamp in
the telemetry was 5.5 minutes fast, ie it had lost approximately 15 minutes
since the previous transmission. By April 13 the onboard clock was just
five seconds fast, and it has stabilised at that value.  Previously the
clock had been gaining one minute per year during the last 21 years.

Investigations into the behaviour of the +Y axis solar array, suggest that
this unit has partially failed. Last year it had been delivering half
current for many months. On December 26th a sudden jump in current was
noticed. Since then current in the +Y axis has only been observed on only
three occassions this year. Two of these occurred early in the year,
immediatly after the beacon switched ON, the other on 12 April.

The next few months will be a challenging time for OSCAR-11, when the solar
eclipses start. Since the last eclipse there has been the partial failure
of the +Y array, and an unidentified additional current drain on the main
14 volt power bus. This might cause problems if the battery voltage falls
below the threshold level of the electronics, perhaps requiring ground
control commands to restart the system.

The internal temperatures have varied randomly, up and down by about three
degrees C.  They are unchanged at 14C, 13C and 20C for the battery,
telemetry electronics and command decoder respectively.  At the present
time the satellite is in full sunlight, and therefore temperature changes
are caused by changes in attitude, and spin rate. The hot external surfaces
will cause some nearby internal parts to warm up faster than others. A
Solar eclipse predictions indicate that the continuous sunlight will
continue until the end of April, when eclipses will start.

The battery voltage has varied between 11.9 and 13.4 volts.  The average
voltage was 12.6 volts, similar to the last report.

The period of rotation about the Z axis had been determined from the solar
array currents.  Values of between 115 and 800 seconds have been observed.
On three occasions it was not possible to measure the spin period, owing to
the unusual attitude of the satellite.

Users of OSCAR-11 should note that the date in the telemetry is now
advanced by FOUR days.

OSCAR-11 now operates in a default mode, controlled by the watch-dog timer.
The satellite transmits continuous ASCII telemetry for approximately 10.3
days on 145.826 MHz., followed by 10.4 days of silence. This regular
sequence might be interrupted by ground control, at any time.

At the present time the mode-S beacon 2401.5 MHz. and the UHF
beacon 453.025 MHz. are both OFF.

Listeners to OSCAR-11 may be interested in visiting my web site.

The web site contains details about using a soundcard for data
capture, and also details about using hardware demodulators. There is
software for capturing data, and decoding ASCII telemetry.
There is an archive of raw data for analysis, which is continually
being expanded, as new data is captured.

The URL is -

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

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT108.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org
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