OSCAR-11 REPORT
27 September 2007
OSCAR-11 is back! During the period 31 August to 27 September 2007, the satellite's 145.826 MHz. beacon has been heard from 16 to 26 September. The switch-on date was later than expected. The solar eclipses finished on 20 August, and previous observations had suggested that the duration of sunlight after 10 August would be sufficient to support continuous operation. However, at the end of last year's eclipse season, some erratic behaviour was also observed.
Unfortunately I was away on holiday when the satellite first switched ON, and only received the data on last two days of transmission. Signals were weaker than those received earlier in the year, ie. before the eclipse season. This has been confirmed by the many reports I have received.
The on-board clock has continued to be of interest. At the end of this ON period the clock was 69.43451 days slow, showing a loss of about 31 days since the previous ON period. The day of the week counter appears to be consistant with the date on the satellite, but has changed in relation to the actual date. Previously, 0 represented Thursday, now it represents Monday.
If the satellite's watchdog timer continues to operate normally, the beacon should switch ON around 06 October 2007.
I am indebted to Peter ZL3TC, Ken W7KKE, Dave G1OCN, Jef KB2M, Graham G3VZV, Martin M0ADY, Gustavo LW2DTZ, John N7ZL, John N3NKC and Thomas HB9SKA for their reports. They were especially useful while I have been away. Many thanks.
The satellite is now in continuous sunlight and this will continue until around 14 November, when there will be a short eclipse season, lasting until around 07 January. However the maximum duration of the eclipses will only be about seven ninutes. At this level the satelite might just survive.
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. More data is required to determine exactly when the date changes.
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 22 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. 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:U2RPT137.CWV, to prevent duplication.
73 Clive G3CWV xxxxx@amsat.org (please replace xxxxx by g3cwv)