E-mail colocado por Pat Gowen, G3IOR na AMSAT-BB e o respectivo comentário do director do projecto do AMSAT-OSCAR-7 Jan King, W3GEY:

From: "pat gowen" <patgowen@btconnect.com>
To: <amsat-bb@AMSAT.Org>
Subject: [amsat-bb] Re: Lazarus?
Date: Fri, 21 Jun 2002 22:30:54 +0100

I have just come across something most remarkable this Friday 21st June evening. Checking out interlopers in our 145.800 - 146.000 MHz space band with a new vertical now atop my 60' tower and working like magic, at 1728 UTC I came across a beacon at S.7 sending slow 8 -10 wpm CW on 145.973.8 MHz. It slowly Dopplered down to 145.970 MHz before going out at 1739 UTC. A full run of TLM went: -

Hi Hi
100 176 164 178
280 262 200 254
375 358 331 354
453 454 461 459
541 501 552 529
600 600 601 651
Hi Hi

It sounded VERY familiar, but, I'm dammned if I can recall which one it was. Obviously an OSCAR, but which had the callsign W3OHI? Oscar-6, 7 or 8? I think it was OSCAR-6. If so, we have a new longevity record, even beating RS-1!

The beacon peaked S9 and there were S7 burbles some 10 - 20 KHz below the beacon, FSK'ing slightly as the beacon keyed. At times the beacon took on a rough quality, wobbling in frequency, then coming back strong and quite stable again. Going by the QSB rate it had about a 1 minute spin.

Could any veteran keen observers (who might look for it) please tell me what it was, as I feel sure that any old time AMSAT OSCAR devotee may have a far better memory than I!

73, Pat, G3IOR

Jan King, W3GEY, the AMSAT-OSCAR-7 Project Manager commented:

[AO-7] has a good set of arrays and the first BCR (battery charge regulator) we ever flew. It's the first spacecraft we ever had that was capable of overcharging the battery. When the battery failed the cells began to fail short. One cell after another failed and the voltage measured on telemetry began to drop. So, the cells were clearly failing SHORT. Now, after all these years, what happens if any one of the cells loses the short and becomes open? Then, the entire power bus becomes unclamped from ground and the spacecraft loads begin to again be powered but, this time only from the arrays. Now you have a daytime only satellite but, each time the sun rises at the spacecraft you have a random generator that either turns on Mode A or Mode B or whatever it wants. So, occasionally that 70cm/2m transponder transmitter and beacon must least work. From what you have told me (and without going back and decoding the old telemetry equations) I can tell you that the following things work in that spacecraft: The arrays, the BCR, the ISR (instrumentation switching regulator), the Mode B transmitter and beacon injection circuitry, the Morse Code telemetry encoder, and the voltage reference circuitry. The latter I know is working because the last telemetry value is 651. The "6" is just the row number of the telemetry value but the 51 means that the 1/2 volt reference is measuring 0.51 volts. I know that telemetry equation by heart since it was used as the calibration value for the rest of the telemetry system. So the telemetry has a fair chance of being decoded and making some sense!!! .  

The full text of W3GEY's comments are here.

Initial reports on the health of AO-7 are:

• Telemetry received may be good or bad. You can determine if the telemetry is good by the 6D value. It is the reference voltage for the analog TLM system and it should be around 50. If not, then the remainder of the telemetry will be incorrect.
• Jan King, W3GEY notes that AO-7 had (has?) a very sensitive receiver and a good uplink antenna. 5 watts EIRP should provide a good downlink. Amplifiers are not required for the uplink. 
• Excessive uplink power may be cause FMing of the transponder and may be causing the input voltage to the regulator that provides 6D to fluctuate causing all telemetry to be bad.
• AO-7 is almost certainly running only off the solar panels. It is very likely to be on only when in the sun and off in eclipse. Since it is resetting each orbit it may not come on every time. Reports of hearing the beacon just as it comes out of eclipse would be particularly interesting.

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Página "Estado do AO-7" actualizada em: 23-07-2008
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