[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

OSCAR-11 Report

                  OSCAR-11 REPORT

                   18 July 2006

RECEPTION REPORTS REQUESTED!  Due to solar eclipses (see below) the VHF
beacon on 145.826 MHz. may only transmit for a short times, perhaps for
only a few orbits, or even less, at irregular intervals. Any reception
reports would be appreciated.  Please e-mail xxxxx@amsat.org (replace xxxxx
by g3cwv), or post to AMSAT-BB. If you are unfamiliar with the sound of
OSCAR-11, there is an audio clip on my website

During the period 15 June to 17 July 2006 nothing has been heard from the
satellite.  It was last heard on 05 May, just one day before the solar
eclipses were due to start. These eclipses will continue until 04 August
2006, reaching a maximum duration of 22% around 19 June. If the satellite
behaves in the same way as it did last year, regular 10 day transmissions
should re-start, sometime in August.

Once again I am indebted to Jeff KB2M, for monitoring the satellite, during
this period.  He has not heard any signals.

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 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.

When last heard, the on-board clock showed a very large accumulated error.
On 05 May it was 22.76456 days slow.  The clock lost two hours during the
last OFF period, and nine hours during the last transmission period. The
observations of clock errors suggest that the clock may slow or stop when
the battery voltage is low.

The watchdog timer now operates on a 20 day cycle. During the three months
before the eclipses started, the ON/OFF times have been very consistent,
and the average of many observations show this to be 20.7 days, ie. 10.3
days ON followed by 10.4 days OFF. However, during the present solar
eclipse season, power supply problems, may result in a low 14 volt line
supply, which may cause the beacon to switch OFF prematurely, and reset the
watchdog timer cycle.

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 which
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

If you place this bulletin on a terrestrial packet network, please
use the bulletin identifier $BID:U2RPT123.CWV, to prevent duplication.

73 Clive G3CWV   xxxxx@amsat.org (please replace xxxxx by g3cwv)
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org