OSCAR-11 REPORT

17 February 2008

This report covers the period from 21 January to 17 February 2008, overlapping the previous report by a few days, to include the two periods of continuous operation.. The satellite was heard from 22 January to 01 February and from 11 February to 15 February.

Signals have been very variable in strength sometimes very strong, sometimes undetectable, even at high elevations. Low signal strength was particularly noticeable at AOS and LOS, and also towards the end of the transmission periods.

The transmission period which started on 11 February was prematurely terminated four days later, on 15 February. If the watchdog timer has reset, it should switch-on again around 07 March. There should be a short period of transmissions before permanent eclipses start in mid March. After March it is unlikely that the satellite will support any sustained period of operation, and will only transmit for a short time, possibly less athn a single orbit, every 21 days.

The real time clock now serves as a crude indicator of the state of the satellite. Between 22 and 29 January the clock was stable to within two seconds. During the next two days it lost 4.3 hours

Between 11 and 15 February the real time clock showed a steady loss of time every orbit. During the four days the clock lost 4.8 hours. When last heard the clock was 82.76424 days slow.

I am indebted to Peter ZL3TC, Chris M0DQO, Tobias DG3LV, Edward BX1AD, Mark KU7Z, Gene WA4UKX, SWL Mark in CM87, Ron G4PGY, Julian WB9YIG and John HB2HSH for their reports. Many thanks.

The satellite is now in continuous sunlight, and this is expected to continue until mid March, when eclipses will start again. Unfortunately eclipses will then become a permanent feature of the orbit, which is likely to prevent any periods of sustained operation after March.

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. 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 23 years in orbit the battery has undergone around 100,000 partial charge/discharge cycles, and observations suggest that it cannot power the satellite during eclipses, or sometimes during periods of poor solar attitude.

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.

The Beacon frequencies are -

VHF 145.826 MHz. AFSK FM ASCII Telemetry

UHF 435.025 MHz. OFF

S-band 2401.5 MHz. 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. There is an example of the latest telemetry received from the satellite. 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.users.zetnet.co.uk/clivew/

If you place this bulletin on a terrestrial packet network, please use the bulletin identifier $BID:U2RPT142.CWV, to prevent duplication.

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