[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                  OSCAR-11 REPORT   14 January 2010

This report covers the period from 30 November 2009 to 14 January 2010.
During this time the satellite was heard briefly on 10 & 11 December and
then from 31 December until 10 January. Good signals were received, and
decoded. Sometimes signals have been very strong, although frequent changes
in polarisation have been observed.  The satellite was not heard
during solar eclipses, which now occur during the afternoon and evening
passes over the UK.

The last two 'off' periods have lasted 14 and 19 days respectively,
suggesting that the watchdog timer has been reset. However, the last
transmission period lasted for the full ten days, so it is possible that
transmissions may resume after ten days of silence, ie. around 20 January.
However, please note that the satellite's behaviour is now very
unpredictable, and until a pattern of operation is established, it is
impossible to predict what will happen next, with any certainty.

The telemetry is unchanged from the 2008 downloads.  The on-board clock
is now 252 days slow. When last received in 2008 it was 83 days slow.
The increasing error suggests that the clock may be stopping, when the
satellite is in eclipse. During the last transmission period the date
failed to increment on one occasion, from 29 to 30 May.


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                RECEPTION REPORTS REQUESTED!

Please send reception reports to xxxxx at amsat.org (replace xxxxx by
g3cwv) or post to amsat-bb.  If you have a file, please discuss it with me,
before sending it!

You may also like to add your reception report to the live satellite status
page, on the website set up by David KD5QGR and Bob WB4APR.  The URL is
http://oscar.dcarr.org/index.php

The satellite transmits on 145.826 MHz., set receiver to NBFM. OSCAR-11
has a characteristic sound, rather like raspy slow morse code, sending
"di di dah dah dah dah dah dah dah" sent over five seconds. If you are
receiving a very weak signal, switch the receiver to CW or SSB. You
should hear several sidebands around the carrier frequency, should be
able to hear the characteristic 'morse code like' sound usually on at least
two of the sidebands.

Please note that you need a clean noise free signal to decode the
signals.  There is an audio clip on my website
www.g3cwv.co,uk  which may be useful for identification
and as test signal for decoding.

                       -------------

Reception reports have been received from Peter ZL3TC, Mike DK3WN, Jon
2M0IBO and Detlef DJ3AK. Many thanks for those.

The Beacon frequencies are -

VHF 145.826 MHz.  AFSK FM  ASCII Telemetry

UHF 435.025 MHz.  OFF

S-band 2401.5 MHz. OFF

The satellite is now subject to eclipses during every orbit.  Long term
predictions indicate that eclipses will occur until 2019, when there will
be some eclipse free periods until 2023.  However these very long term
predictions should be regarded with caution, as large tracking errors can
accumulate over long periods of time.

When analogue telemetry was last received in March 2005, 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 25 years in orbit the battery
has undergone over 100,000 partial charge/discharge cycles, and
observations suggest that it cannot power the satellite during eclipses
lasting more than about ten minutes, or sometimes even during periods of
poor solar attitude.

Study of the satellite's behaviour prior to 2008 suggested that its
battery would not sustain operation during solar eclipses, and the watchdog
timer would switch the satellite OFF after less than an orbit.  Eclipses
are now occur during every orbit and will continue for many years. In
practice this meant that OSCAR-11 would only be heard occasionally by
stations monitoring the frequency while listening for other satellites.

The satellite unexpectedly started sustained transmissions during
November 2009, suggesting that there may have been a failure causing
reduced drain on the power supplies or a change in the watchdog timer
characteristics.

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 are still working. The real time clock is showing a large accumulated
error, although over short periods timekeeping is accurate to a few seconds
per month.  The day of the month has a bit stuck at 'one' so the day of the
month may show an error of +40 days for some dates.  The time display has
switched into 12 hour mode. Unfortunately, there is no AM/PM indicator,
since the time display format was designed for 24 hour mode.

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.

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.

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 last telemetry received from the satellite is available
for download. 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 www.g3cwv.co.uk Please note that my old website
www.users.zetnet.co.uk/clivew is no longer being updated, athough it may
still be available.

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT146.CWV, to prevent duplication.

73 Clive G3CWV   xxxxx at amsat.org (please replace xxxxx by g3cwv)