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.

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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@amsat.org (please replace xxxxx by g3cwv)