Satgen389  Amsat Oscar 10 - Cause for Concern ?  by GM4IHJ    7 Sep 96

   Until recently , the benign deterioration of Ao10 has had little 
reporting. Control of the satellite was lost some years ago , when
damaged caused by its radiation plagued orbit , finally destroyed
onboard control, and it ceased to respond to ground commands,
remaining permanently in mode B. Since when the simple rule has been 
" Use it , provided its 145.81 Mhz beacon signal is not FMing". Recent
observation suggests that , that rule may now need amplification.

   The easiest and only way to monitor Ao10s state is via its beacon.
For several years the beacon has shown a clear pattern whereby the
beacon was steady and hence Ao10 was usable, when for a month or two
the satellites attitude in space resulted in satisfactory power
production from effectively illuminated solar panels. Alternating with
other periods of months when the FMing beacon indicated poor power
generation and hence poor communications capabilities. This situation
was not of great concern noting that Ao13 was providing most of the
long range communication radio amateurs needed.

   That is no longer the case. A013 is not going to be useful for very
much longer. So some radio amateurs are begining to return to Ao10,
apparently ignoring the fact that its beacon is clearly FMing , and
hence its power supplies are suffering.

   For the past 3 months Ao10s beacon has been FMing . The frequency
excursions have been of the order of 50 to 75 Hz, and they have been
synchronised to a pattern of signal strength variation which
fluctuated between 0 dB and 10 dBs signal to noise ratio, roughly 7
times every minute.

   Despite the obvious , clearly audible, frequency instability of the
beacon , a number of European stations have begun to try to use it. In
a typical sequence on 30th Aug 96 , Ao10 was detected at IHJs western
horizon as its foootprint left USA and the Caribbean , and moved over
to Europe at about 1810 utc. For 2 minutes the beacon frequency
fluctuated rhythmically 7 times per minute over a range of about 50 to
70 Hz. Then at 1812 ut as the footprint enter mainland Europe the
situation changed dramatically. Suddenly the rhythmic change
disappeared to be replaced by a massive irregular patternless
frequency shift peaking at times at more than 250 Hz , as Europeans
began accessing the transponder and totally depressing its power
supply bus voltage. The results were awful. The beacon note became a
rough fluttering howl, and the so called qsos were quite dreadful. In
a typical sequence one European asked another to repeat his callsign 5
times, before he copied it correctly. He then gave him a 59 report.

   Given that Ao13 will not be with us much longer, it is likely that
more people will try Ao10, many of them blissfully unaware of its
short comings and fragility, when its panels are not at a good sun
angle. Widespread dissemination of information about the true state of
Ao10 would appear to be necessary if we are to avoid damage to the
satellite. With patience it will probably adopt a good sun angle soon
and give good qsos. That is, if the idiots do not kill it first.