[amsat-bb] OSCAR-11 Report

Tue Dec 1 02:12:38 PST 2009

                            OSCAR-11 REPORT   30 November 2009

This report covers the period from 21 April 2008 to 30 November 2009.

The satellite unexpectedly resumed transmissions recently.  It was first 
heard by Keith N4ZQ on 19 November 2009 and transmissions continued 
until it switched OFF on 27 November.  It was last heard by Tetsu JA0CAW 
at 23:59 UTC 26 November 2009. Previously, it was last heard by Peter 
ZL3TC on 23 April 2008, on a single pass.

Study of the satellite's behaviour had 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.

During this period of inactivity the satellite achieved 25 years in 
orbit on 01 March 2009. Congratualtions to Professor Sir Martin 
Sweeting, his team at the University of Surrey and participating amateur 
radio groups, for this fine achievment.

Good signals have been received by stations located all over the world 
during this  recent period of activity and telemetry has been decoded 
successfully. However, the satellite has only transmitted when in 
sunlight. I have been overwhelmed by the number of reports received, too 
many to list individually!  Many thanks to everyone who sent email 
reports or posted to AMSAT-BB.

The telemetry is unchanged from the 2008 downloads.  The on-board clock 
is now 241 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.

The exact date when the satellite started transmitting is not known, so 
if the watchdog timer was reset, the next transmissions might start 
around 16 December, however if the timer went through its full operating 
cycle, transmissions could resume around 06 December.

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 telemetry was last received 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.

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

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 let me know what
you have, before sending it!

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 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 OLD website 
www.users.zetnet.co.uk/clivew/  which may be useful for identification 
and as test signal for decoding.

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

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. When last heard the clock was 241 days slow.  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.

OSCAR-11 was the second satellite from the University of Surrey,
www.ee.surrey.ac.uk/SSC.  It was designed, built and launched, within a
time scale of six months, by a team headed by Martin Sweeting G3YJO.
Amateur radio groups working at various locations in the world, also
contributed to the project. It used commercially available 'off the shelf'
components (COTS). Following the success of these satellites, in 1985
Surrey Satellite Technology Ltd. www.sstl.co.uk was formed, as a commercial
venture. This grew into a major company which has produced over 30 small
satellite projects for a global market.

The University of Surrey has recently sold it's major
shareholding in SSTL to EADS-Astrium.  The joint company will therefore 
have the experience of manufacturing large and small satellites, for 
geo-synchronous and low earth orbits.

In regognition of his work, Martin G3YJO, was appointed Professor at the
University of Surrey.  He received an OBE in the 1995 Queens birthday
honours list, and in 2002 a knighthood in the New Year's honours list.

Listeners to OSCAR-11 may be interested in visiting my websites. 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 has now been updated. 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.users.zetnet.co.uk/clivew/     However, please note that this site 
is no longer being updated, and the latest news and information will and 
will be uploaded to my new site  www.g3cwv.co.uk which is currently 
being constructed.

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT145.CWV, to prevent duplication.

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