[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                    OSCAR-11 REPORT

                   29 December 2006


During the period 20 November to 29 December, the satellite was heard
from 28 November to 08 December and from 18 to 28 December. Good,
steady, often strong, signals have beeen heard on all passes, and
excellent copy of the telemetry obtained.

The date/time stamp has been of continued interest.  Since the satellite
was heard on 18 October the on-board clock has maintained accurate time, to
within five seconds over a period of 71 days. This compares with the average
gain of five seconds per month, recorded when the satellite was fully
operational.

The date counter appears to be incrementing correctly, but the day of the
month is not reset to one, at the end of each month, and is not
incrementing the month counter correctly. During the last OFF period the month
counter changed from '10' to '11'. On 28 December the date was shown as 61
November. However, the day of the week counter appears to be incrementing
correctly. Currently, 0 indicates Thursday.

If the satellite's watchdog timer continues to operate normally, the beacon
should switch ON around 08 January 2007. The satellite is in full sunlight
at the present time, and will remain in this state until mid-April 2007,
when eclipses start again.

I am indebted to Peter ZL3TC, Dean AL7CR, Bob G4VRC and Ken W7KKE  for
their reports. Reports around the times of the expected beacon switch
ON/OFF, are especially useful.  Many thanks.

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 were still working. 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:U2RPT128.CWV, to prevent duplication.

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