[amsat-bb] OSCAR-11 Report

Wed May 16 01:15:00 PDT 2007

                    OSCAR-11 REPORT

                     16 May 2007

RECEPTION REPORTS REQUESTED!

OSCAR-11 might switch ON around 18/19 May and possibly 8/9 June.  However,
due to solar eclipses the satellite is likely to switch OFF, almost
immediately, probably after less that one orbit.  This brief period of
activity could occur when the satellite is over any part of the world.
Due to the condition of the satellite, there is no guarantee that these
predictions are reliable, during the eclipse season.

Any reception reports would be grately appreciated. Please send 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 17 April to 15 May 2007, the satellite's 145.826 MHz.
beacon was heard from 22 to 28 April. The beacon switched ON
as expected. This short period was of special interest since the
solar eclipses started on 21 April and steadily increased each day,
reaching a duration of 12.6 minutes when the beacon switched OFF. Thus it
was an rare oportunity to study the effect of solar eclipses on the
satellite.

Good signals were heard on most passes, although they became weaker towards
the end of the ON period. Good copy of the telemetry was obtained.

The on-board clock has continued to be of interest.  At the start of this ON
period the clock was 38.21438 days slow, showing a loss of about 3 seconds
since the previous ON period. For the next four days the clock remained
stable, however by 07:14 UTC 28 April the clock had lost a further 220
minutes. On the next two passes the clock lost 20.3 and 20.6 minutes
respectively, ie. almost twice the duration of the eclipses.

When last heard the total clock error was 38.39593 days slow.

Peter, ZL3TC reported hearing the satellite switch ON, after coming out of
eclipse at 08:14 on 28 April.   These observations suggest that the
satellite's electronics may be suffering from low power supplies, before
the watchgog timer cycle finally resets.

If the satellite's watchdog timer continues to operate normally, the beacon
should switch ON around 19 May 2007. However, the duration of the solar
eclipses at that time is 23.4 minutes. This could cause the beacon to
switch OFF. after a short time, probably less than one orbit. This short
transmission could occur any where over the world, and could be repeated at
20.7 day intervals, until August when longer transmissions are likely.
expected to start on 20 April and will continue until 20 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. Maximum eclipse duration of 23
minutes occurs on 14 June and it decreases to 12 minutes by 10 August. At
that level, the satellite might start transmitting.

I am indebted to Ian ZL1AOX, Peter ZL3TC, David G8OQW, Jeff KB2M, Edward
BX1AD, Sil ZL2CIA, Gene
Dave G1OCN, John K8YSE and Grant VK4JAZ 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 09 hours UTC.
Unfortunately, there is no AM/PM indicator, since the time display format
was designed for 24 hour mode.

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:U2RPT133.CWV, to prevent duplication.

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