[amsat-bb] OSCAR-11 Report

[Clive Wallis]

                    OSCAR-11 REPORT

                   31 October 2006

OSCAR-11 is back!  It was first heard by Peter ZL3TC, at 06:23 UTC on
October 18. It had been silent since August 26.

During the period 28 September to 30 October, the satellite was heard
from 18 to 28 October. Good signals have been heard on most passes, often
very strong.

Further deterioration of the time/date stamp has occurred.  Here is a
frame of telemetry captured on 27 October at 08:43:51 UTC.

UOSAT-2           060=601033448

000000010001020002030003040004050005060006070007080008090009
100001110000120003130002140005150004160007170006180009190008
20000221000322000023000124000625000726000427000528000A29000B
30000331000232000133000034000735000636000537000438000B39000A
40000441000542000643000744000045000146000247000348000C49000D
50000551000452000753000654000155000056000357000258000D59000C
60800E615FC1620105633305644402651E0C662AC467000168000E69000F

The date/time stamp is the block of characters following 'UOSAT-2' having
the format YYMMDDWHHMMSS (Year, month, day, day of week, hours, minutes,
seconds).

The month, shown as '0=' in the date stamp is now in all telemetry frames.
When the satellite was heard in August the month, had stuck at 07 and the
day had incremented to 60. During the ten day reception period in October,
the day had correctly incremented from 51 to 60. While the satellite was
silent, it appears likely that the day may have incremented to 99 and then
reset to zero.  It will be interesting verify this theory on future passes.

During the last ten days of beacon transmission the time stamp
incremented accurately, and no gain or loss was detected ( within one or
two seconds).  However, on one occasion, the most significant digit of the
hours failed to change from zero to one, although it didn't  cause a
permanent error.

If the satellite continues to operate normally, the beacon should switch ON
around 07 November. If nothing is heard, it may be worth listening ten days
later, ie. around 17 November.


I am indebted  Peter ZL3TC, Bob G4VRC, Paul KB5M, and Doug KA2UPW/5 for
their reports and for monitoring the satellite. Peter listened for the
satellite daily, often during several passes, while it was silent.  Many
thanks.

The status of the satellite, when last heard, was 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:U2RPT126.CWV, to prevent duplication.

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