[amsat-bb] OSCAR-11 Report

[Clive Wallis]

         OSCAR-11 REPORT

         24 February 2010

This report covers the period from 11 January to 23 February 2010. 
During this time the satellite was heard from 21 to 31 January and 11 to 
24February. Good signals were received, and decoded. Signals have been 
very strong, although frequent changes in polarisation have been 
observed. The satellite has only transmitted when in sunlight.

The next transmissions are expected around 04 March 2010.

The on-board clock was 260 days slow, when last heard on 21 February. 
The increasing error suggests that the clock may be stopping, when the
satellite is in eclipse. Sometimes, the date counter also fails to
increment.

Reception reports have been received from stations located all over the
world including Peter Zl3TC, Jon 2M0IBO, Mike DK3WN, Adrian LU1CBG, 
Robert VE2PRS, Ken GW1FKY and Alan ZL2BX. Many thanks to everyone who 
sent email reports, posted to AMSAT-BB or updated the KD5QGR/WB4APR 
satellite status website.

The Beacon frequencies are -

VHF 145.826 MHz. AFSK FM ASCII Telemetry

UHF 435.025 MHz. OFF

S-band 2401.5 MHz. OFF

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

RECEPTION REPORTS REQUESTED!

I am particularly interested in reports of reception during the hours 
23:00 to 06:00 and 12:00 to 17:00 UTC, especially near expected switch 
on or off dates.

Please send reception reports to xxxxx at amsat.org (replace xxxxx by
g3cwv) or post to amsat-bb. If you have a file, please do not send it 
but let me know what is available.

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, and should 
be able to hear the characteristic 'morse code like' sound on at least 
one sideband.

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.

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

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 eclipses started around 2005 the watchdog timer often switched the
transmitter off before the ten day on period had finished, during parts
of the
eclipse cycle. When eclipses became a permanent feature of all orbits,
after April 2008, the transmitter switched off within a single orbit, 
thus the satellite was effectively non operational.

The satellite unexpectedly started regular transmissions in November 
2009. It is possible that a fault has developed, which prevents the 
watchdog timer resetting when the power supply fails. The transmitter 
switches off during eclipses, and the real time clock stops during most 
of the eclipse.

When analogue telemetry was last received, in 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 indicate that it cannot power the satellite during eclipses.

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 during ten minute passes the clock 
increments correctly to within one second. 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 day s ON followed by 10.4 days OFF.

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 which is updated from time to time. 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 .

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT147.CWV, to prevent duplication.

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