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.

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RECEPTION REPORTS REQUESTED!

Please send reception reports to xxxxx@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.

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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@amsat.org (please replace xxxxx by g3cwv)