Satgen 472  Ao10 End Game ?   by GM4IHJ  (BID SGEN472)   98-04-11

On April 5th 1998 , Amsat Oscar 10 mode B 435MHz up, 145 MHz down,
beacon 145.81 Mhz, was operating usefully as it has done for some
time, with its downlink beacon signal fading once every 50 seconds,
with every 3rd fade being deeper than the other two. In addition since
29 March 98 the beacon had begun to FM slightly, with the FMing
increasing each day up to 5th April when shifts up to 60 Hz were
occuring every 50 seconds , with minor shifts evident in between these
big shifts.

On April 6th 1998, everything changed. The beacon which on previous
days had been peaking at 20 dBs over noise , suddenly dropped right
down, being absent completely except for 10 or so seconds every 50
seconds, when it reappeared briefly out of receiver noise. Using an
FFTDSP display the signal could be seen almost continuously , where by
it was seen to be FMing up to 110Hz in a relatively fixed pattern
every 50 seconds.

At no time before 5th April was the FMing coincident with hipowered
signals on the transponder. Indeed the very marked repeat of FMing
pattern every 50 seconds indicated that the FMing was in phase with
some feature of the satellites very slow spin or multiple axis
tumbling. Whereby the satellites power supplies were varying wildly as
solar panels saw the sun only briefly for a few seconds at a time.

It is too early to guess what the future holds for Oscar 10. But it is
clear, now that the satellite has ceased to be spin stabilized, that
we can expect its performance to be highly irregular. That is ,if it
ever actuallly does return to even a much reduced operational state. A
situation which is to be hoped for, but which is by no means certain
at this time. What we are seeing now , plainly has nothing to do with
eclipses or poor general insolation factors which affected the
satellite in the past. These problems of the past are in no way
responsible for Oscar Ten's present predicament. 

What else might we do to get more information ? Certainly there is no
hope of much electronic information although even simple recordings of
comparisons of transponded uplinked signals versus beacon signals
might tell us something. Whilst if someone has a telescope and CCD
camera capable of imaging Ao10 at night, the record of sunlight
reflected from it might be very informative.

It is appreciated that the above is a very imprecise report of what is
actually happening to Oscar Ten. Without downlink telemetry we cannot
say very much. But having a satellite which has survived for 15 years
is itself unique. Most satellites expire for one reason or another
long before they reach this advanced age. Which makes it well worth
while monitoring Ao10 every now and again, and using it if possible,
just to get a record of this part of its life cycle.