The RESURRECTION and the light (or Illumination) 

This data courtesy AMSAT/ Jan King W3GEY.

"I am certain what has happened (and I know why): The battery did fail short. Virtually all of the cells failed in a shorted mode eventually. This shorted condition placed a shunt across the solar arrays and prevented current from going to the satellite loads (i.e. the transponders, in particular). Some time before G3IOR reported hearing the spacecraft again the short on one of the cells (1 out of 10) failed a second time. This time, it went from short to "open." When it went open this released the shunt that was pulling the array voltage down and allowed the current to pass to the satellite loads.

Since there is no battery at all now (because one cell went open), when AO-7 goes into eclipse with each orbit, the satellite has no power to operate and shuts down in the dark. The AO-7 satellite system predates microprocessors so, in those days we used a logic system to control the operation of the satellite system. Some of the features of that logic system (called the Experiment Control Logic or ECL) seem to be working and some not.

One feature that doesn't seem to work correctly without the battery is a thing called the initial condition generator (ICG). This circuit is supposed to put the satellite, if I recall correctly, into Mode D with one of the beacons going after separation from the launch vehicle. When the satellite comes out of eclipse without a battery, it should think it is being released from the launcher again. Instead, the satellite is randomly reset as it goes into eclipse and comes up in a random mode as has been observed. We seem to have one of two command decoders working and the morse code telemetry system is working very nicely.

The telemetry is very interesting and it was totally scarry to decode the first block of that stuff last year. It was like seeing a ghost for me. You have no idea how emotionally this effected me. Seems strange but, I lived with that thing in the same way someone else would live with a child. I was 27 years old then and my first child was born the same year as the launch. I'm 56 now. So, to have it "tell me" what it was doing after being asleep for all those years was very strange indeed.

It appears that the 24 hour clock that would cycle the transponders between modes A and B is working but, it gets reset every time the satellite goes into eclipse. We could control the mode reasonably well if we could catch the satellite as it comes out of eclipse each time and command it to the desired mode.

There is another OLD problem though, which works against keeping it under control. We always had great difficulty commanding the satellite while it is in Mode B. The receiver is being interfered with by the transmitter in the transponder. This was never a problem when we had a battery as the 24 hour timer always brought it back to Mode A after 1 day and we had control again. So, unless you have mega-power at the command station you can't do much with it while it is in Mode B or C. I also don't know if it is being regularly commanded. I doubt it. If you can get people interested in controlling it, then we could make arrangements to show them how to command it.

So, it probably will be mostly a random satellite, however, when it is in Mode A we could send quite a few interesting commands that would allow users to investigate various equipment on board. One thing that hasn't been played with is an on-board data system called Code Store. It was an early fore-runner to packet radio. I don't think anyone knows if that still works but, we do have a box in the AMSAT Museum that can upload data to that experiment.

People should realize that the solar arrays are old and they don't put out more than a few watts now. That's the only power available to run the transponders. So, if they uplink too much power it will just cause the transmitter to sort of "cave in." The voltage on the satellite bus begins to sag badly when a heavy demand is placed on the transponder (by a large uplinking signal) since there is nothing there to regulate it and then the oscillators in the receiver and transmitter chain start changing frequency. People call this "FMing" and that is what is going on.

AO-7 was a major chapter of my life! This whole experience of having it come back is pretty strange stuff to all of aerospace, not just amateur radio.

- Jan King, W3GEY, AO-7 Project Manager