[amsat-bb] OSCAR-11 Report

Clive Wallis clivew at zetnet.co.uk
Wed Apr 18 03:37:58 PDT 2007


                    OSCAR-11 REPORT

                     18 April 2007

RECEPTION REPORTS REQUESTED!

OSCAR-11 is expected to switch ON around 22:00 UTC 21 April.  This is just
after the start of solar eclipses, which may cause the satellite to switch OFF
for 21 days. In the past the satellite has been very sensitive to the start
of eclipse season, although the duration of the eclipses is initially very
short. Please send reception reports to the the address below or post to
amsat-bb. If you are able to record the satellite as a WAV file, please do
so, but let me know what you have, before sending it!

If you need to hear what the satellite sounds like, please visit my website
www.users.zetnet.co.uk/clivew/  The satellite transmits on 145.826 MHz. set
receiver to NBFM.

                         ---------

During the period 22 March to 17 April 2007, the satellite's 145.826 MHz.
beacon was heard from 01 to 11 April . Excellent signals have beeen heard
on most passes, and good copy of the telemetry obtained.

The on-board clock has continued to be of interest.  At the start of this ON
period the clock was 37.21439 days slow. During this period, the date
passed through the transition from February to March. Instead of changing
the month after 28 February, the date incremented to 29 February, and then
changed to 01 March. Previously, since 1992, a fault had occurred every
leap year, when date had failed to increment to 29 February.

When last heard the total clock error was 38.21441 days slow.

If the satellite's watchdog timer continues to operate normally, the beacon
should switch ON around 21/22 April 2007. However, solar eclipses are
expected to start on 20 April and will continue until 23 August. If the
satellite performs as it did last year, it is unlikely to be heard, for any
length of time, during the eclipse season.

I am indebted to David G8OQW, Jeff KB2M, Edward BX1AD, Sil ZL2CIA, Gene
WA4UKX and Rik, ON4GJ for their reports. 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 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 is showing an error of +40 days.  The time display has
switched into 12 hour mode, with the date changing at around 05 hours UTC.

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:U2RPT132.CWV, to prevent duplication.

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


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