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OSCAR-11 Report




                OSCAR-11 REPORT    16 June 2002

The period from 17 May to 14 June 2002 has been an interesting
time for OSCAR-11.  In mid November 2001 the Z-axis attitude
correction reached its saturation value of 1024, which stopped all
attitude and spin correction magnetorquer pulses.  The Z axis
attitude was controlled solely by the passive gravity boom gradient.
There was no control of the spin rate.  Between November and March
the spin period varied randomly between 179 and 237 seconds. During
April and early May the spin rate started to slow down reaching a
period of 1901 seconds (32 minutes per revolution) on 20 May.

On May 21 ground control reset the attitude counters, started a new
WOD survey, and corrected the date anomaly in the status frames.
Initially there was a steady stream of Z pulses, but very few
negative spin pulses.  This had little effect on the slow spin
rotation, which even changed direction. An erroneous spin period of
+87 seconds was noted on one occassion.  However after 10 days the
spin period quickly reduced to -343 seconds, and normal spin counts
were observed.  On 14 June the spin period was -363 with zero
positive and 103 negative spin counts.

The SEU count rate has also been of interest this month. Since mid
May 2001 the rate at which SEU counter changes had been steadily
increasing as memory locations failed.  However this rate has now
stabilised at 1150 counts per day. Decoding the SEU binary
telemetry shows six memory locations 39C0, 21C0 3EC0, 37B1, 180 and
F96 have failed. These permanent memory failures tend to mask out the
display of the less frequent failures, owing to the limited storage
for this data in the satellite. A program for decoding the SEU
packets (U2PKT.ZIP) may be downloaded from my website. URL details
below.

Reception of the 145.826 MHz. beacon has varied between good and
poor.  Poor reception sometimes occurred when the spin rate was very
slow. The 435.025 MHz. was heard on 21 May during ground control
operations.  Good signals were received, stronger than those received
many years ago when this beacon was frequently heard (my equipment is
unchanged).

The internal temperatures have decreased by one degree C. They are
now 0.0 C and -1.2C for battery and telemetry electronics respectively.
However, during the spin rate anomaly the temperatures were depressed
by a further one degree C, and changed at different rates.

The battery voltage observed during daylight passes has decreased by
0.4 volts. The average value observed was 13.0 with a range of 12.2
to 13.6 volts.  The very low voltages were observed during the spin
rate anomaly.

The WOD survey of channels 10, 20, 30, 40 ( +Y, -X, +X array
currents, & array voltage ) dated 06 January 2002 was transmitted
until 21 May when it was replaced by a new survey of channels 1, 2,
3, 61 (X, Z, Y magnetometers and status) dated 22 May 2002.  This new
survey shows the unusually long spin period of 1800 seconds.  Both
WODs may now be downloaded from my web site, details below.

The mode-S beacon on 2401.5 MHz. has been heard by Christian F1AFZ,
Michael OH2AUE, Jerry K5OE, and Bruce SM0TER/K3ZAQ.  Christian
reported good signals, and observed two carriers separated by 1200
Hz., ie the modulation frequency. Michael received signals during an
overhead pass, using a simple feed horn. Jerry received the beacon on
a 20 degree pass using a 60 cm dish with a K3TZ patch and TSI 3731
converter.  Bruce received S2 - S4 signals on his two metre dish,
without AZ-EL control and without Doppler correction on his
receiver. Many thanks for those reports.

The operating schedule is unchanged.

        ASCII status (210 seconds)
        ASCII bulletin  (60 seconds)
        BINARY SEU (30 seconds)
        ASCII TLM (90 seconds)
        ASCII WOD (120 seconds)
        ASCII bulletin (60 seconds)
        BINARY ENG (30 seconds)

The ASCII bulletin (number 115) is currently a static message,
detailing modes and frequencies of some amateur radio satellites.

There  are  additional  status  blocks  after  each bulletin is
transmitted, and between ASCII TLM and WOD.

The mode-S beacon is ON, nominally transmitting an unmodulated
carrier on 2401.5 MHz. There is however a VERY low level of AFSK
modulation which has been detected on strong signals. Telemetry
indicates that the beacon has partially failed, and is delivering
half power.  This beacon is a useful test source for those testing
mode-S converters, as an alternative to OSCAR-40. However the signals
are very weak, and there is a lot of Doppler. Users should also note
that the polarisation of OSCAR-11 is LHC. Even if you can't hear
OSCAR-11, your equipment may still be OK for OSCAR-40. Any reports
of reception on 2401.5 MHz. would be most welcome.  Please e-mail
g3cwv@amsat.org.

The 435.025 MHz. beacon is normally OFF.  However it can sometimes be
heard when the satellite is being commanded by ground control, ie.
within range of Guildford, UK.  When the 435 beacon is transmitting,
the 145 beacon is normally OFF.  The data transmitted is mainly
binary.

Listeners to OSCAR-11 may be interested in visiting my web site.  The
web site contains details of hardware required and some software for
capturing data, and decoding ASCII telemetry and WOD.  There is an
archive of raw data (mainly WOD) for analysis, which is continually
being expanded, as new data is captured.  Also included are some
audio files, examples of each type of data transmitted by OSCAR-11,
each one plays for about ten seconds.  There are also examples of
mode-S reception.  All the audio files are zipped, so that they can
be played off-line.  These should help listeners identify the various
types of data, and give an indication of the signal quality required
for successful decoding.

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:U2RPT73.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org

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