OSCAR-11 REPORT 30 March 2010

OSCAR-11 achieved 26 years in orbit on 01 March! It was designed, built and launched within a period of six months, using commercially available 'off the shelf' components (COTS). Once again, congratulations to Professor Sir Martin Sweeting G3YJO, his team at the University of Surrey and groups of radio amateurs who also contributed to the project. Unfortunately, the satellite wasn't transmitting on its birthday, but was heard briefly, three days later.

This report covers the period from 23 February to 30 March 2010. During this time the satellite was heard during three passes on 04 March. Good signals were received, and decoded. There was also an unconfirmed report that it was heard on 25 March.

Due to eclipses, deterioration of the battery and other parts of the satellite, it's not possible to predict when the satellite will be heard in the coming months. It is likely that it may be heard occassionally, by stations tuning around the beacon frequency.

The on-board clock was 263 days slow, when last heard on 04 March. The increasing error suggests that the clock may be stopping, when the satellite is in eclipse. Sometimes, the date counter also fails to increment. However, the retention of the date and time does suggest that a small amount of power may be still available during eclipses.

The Beacon frequencies are -

VHF 145.826 MHz. AFSK FM ASCII Telemetry

UHF 435.025 MHz. OFF

S-band 2401.5 MHz. OFF

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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 do not send it but let me know that it 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 a period of 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, and your receiver must be set to NBFM mode, for a decoder to work.

If you need to know what OSCAR-11 sounds like, there is an audio clip on my website www.g3cwv.co.uk/ which may be useful for identification and as a test signal for decoding.

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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. Although there was a small variation in the length of eclipses, this wasn't enough to explain why the satellite started regular transmissions. It is possible that a fault developed, which prevented the watchdog timer resetting when the power supply fails, and now the watchdog timer settings are no longer retained during eclipses. 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 26 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 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:U2RPT148.CWV, to prevent duplication.

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