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OSCAR-11 Report



                  OSCAR-11 REPORT

                  15 October 2004

I have recently updated the telemetry archive on my website to include
telemetry for January to August 2004. There is also a file of recent
telemetry data, RECTLM.ZIP which is updated each month.  This month it is
for 07 October, mentioned below.  URL www.users.zetnet.co.uk/clivew/

During the period 24 September to 14 October 2004 the 145.826 MHz. beacon
has been heard transmitting continuous ASCII telemetry from 03 to 12
October. During this period good signals have been received.

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 23 October.

The telemetry has indicated two interesting changes, which have occurred
recently.

Firstly, the 14 volt line current has increased from around 515 mA to 925
mA between 22 September and 03 October. The line current increase appears
to be consistent with changes in array current and battery current, so is
probably correct.  I can't see any other currents or temperatures which
have unexpectively increased.

Secondly, the Y axis magnetometer shows different spin rates in the X and Y
axes, indicating a very unusual motion. On 08 October the Y rate was half
the X rate. However, the relationship between the two is never the same,
and each graph shows a different picture.

I wonder if these two events are connected? The amount of current is about
the same as taken by two magnetorquer coils.  However, the magnetometers
are not picking up a steady field. In the past the maganetorquer pulses
tended to saturate the magnotometers, when all was working normally ie.
the spin under active control. Could a fault in the magnetorquer switches
cause opposing currents in the two coils, and perhaps leave a small
residual magnetic field, which might cause some strange effects?

The internal temperatures have remained fairly constant, although there has
been some random variation, caused by the unusual attitude, reported above.
They are now 18.2C, 17C and 22.8C for battery, telemetry electronics and
command decoder, respectively. Solar eclipse predictions indicate that the
satellite is now in continuous sunlight, which will continue for the
remainder of the year.

The battery voltage observed during daylight passes has varied between 10.6
and 13.0 volts.  The average voltage has dropped to 12.4 volts. The lower
voltage is being caused by the extra current being taken from the 14 volt
line, and poor attitude.

Users of OSCAR-11 should note that the date in the telemetry is now
advanced by FOUR days.  The time is advanced by 20.3 minutes, and this
error is increasing by about one minute per year.

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.

The mode-S beacon is ON continuously, even when the VHF beacon is OFF,
nominally transmitting an unmodulated carrier on 2401.5 MHz. There is
however a VERY low level of AFSK modulation, (now a constant audio tone),
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. 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.  Any reports of reception
on 2401.5 MHz. would be most welcome, however please DO NOT send sound
files.  Please e-mail g3cwv@amsat.org.

The 435.025 MHz. beacon is normally OFF.  It can only be heard on the
very rare occassions when the satellite is being commanded by ground
control, ie. within range of Guildford, UK.  When the 435 MHz beacon is
transmitting, the 145 MHz 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 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.  Originally this was for
WOD, but it is now being expanded to include ASCII telemetry. At the
present time the telemetry covers 1996 to April 2003.  I will add
other years as time permits.  In parallel there is a news archive
which provides an overview of the state of the satellite, at the
times when the telemetry was captured.

If anyone out there can provide any data, particularly for the 1984
to 1993 years, this would be most appreciated.  Please e-mail me
with details.  However please DO NOT SEND ANY FILES, before futher
discussion.

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:U2RPT102.CWV, to prevent duplication.

73 Clive G3CWV   g3cwv@amsat.org
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