[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                    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 at amsat.org (please replace xxxxx by g3cwv)