[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                    OSCAR-11 REPORT

                    26 January 2008


This report covers the period from 19 December 2007 to 26 January 2008.
After two months of silence from 20 November, when eclipses started, the
satellite resumed transmissions on 22 January 2008. This was three complete
20.7 day watchdog cycles after the satellite switched off. At the time of
writing signals are consistantly strong, although the polarisation is very
variable, with a cycle time of around 20 seconds, causing deep fading if
the antenna polarisation is fixed. This suggests that the satellite may be
tumbling.

If the current watchdog cycle continues uninterrupted, the 145.826 Mhz.
beacon should switch off around 01 February and on again around 11
February. However, if low battery voltage causes the watchdog timer to
reset, then the beacon should switch on 21 days later.

The real time clock in now very stable although it has lost a further 7.09
days since 20 November. On 26 January it is 81.36403 days slow.

I am indebted to Peter ZL3TC, Mark KU7Z, Gene WA4UKX, SWL Mark in CM87, Ron
G4PGY, Julian WB9YIG, John HB2HSH and Edward BX1AD 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.
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 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:U2RPT141.CWV, to prevent duplication.

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