[amsat-bb] OSCAR-11 Report

Clive Wallis clivew at zetnet.co.uk
Tue Jan 23 04:49:47 PST 2007

                    OSCAR-11 REPORT

                   23 Jnauary 2007


To investigate the date problem mentioned below, I would welcome some
telemetry from differents parts of the world, at times when the orbits do
not pass over the UK. These times are approximately from 10:00 to 16:00 and
from 19:00 to 04:00 UTC. If you don't have a decoder, I can now accept
short WAV files of good audio, duration up to 30 seconds.

I would also like reports of reception around the times of expected beacon
switch ON and OFF. No telemetry wanted, just when you listen, and whether
you heard, or didn't hear the bird. Please e-mail to the address below.

During the period 29 December 2006 to 23 January 2007, the satellite was
heard from 08 to 18 January. Good steady signals have beeen heard on all
passes, and excellent copy of the telemetry obtained.

The on-board clock has maintained accurate time, over the reporting period,
gaining 2.5 seconds. However the hour counter sometimes shows an error of
of 10 hours, ie. in its most significent digit. The 'day of the week'
counter operates reliably, zero representing Thursday.

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.  Possibly, it resets
to 41, ie. the unused bit representing 40 permanently stuck at a one. On 17
January the date was shown as 51 December 2006.  Further investigation is
required to establish exactly how the date connter changes.

If the satellite's watchdog timer continues to operate normally, the beacon
should switch ON around 28/29 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 Bob G4VRC and Dean AL7CR for their reports. Reports around
the times of the expected beacon switch ON/OFF, are especially useful. Many

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:U2RPT129.CWV, to prevent duplication.

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

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