Satgen 462  Oscar Ten . No Spin ?  by GM4IHJ (BID SGEN462)  1998-01-31

For many years now, Oscar Ten has operated Mode B (435 up 145 down),
only when its solar cells were seeing the Sun. It has not been
answering ground control signals for years.So its attitude pointing in
space is relatively unpredictable and hence we have difficulty
predicting when it will get enough sunshine to operate properly
without serious FMing, or, complete shut down. When it is in good form
Oscar Ten can be a delight to operate , and it has never suffered from
the spin modulation which so affected Oscar 13 communications. But
gradually over the last year or so a problem has become more apparent.
Whereby, even when well illuminated by the sun, long range DX contacts
generally between stations in different hemispheres, gave very poor or
no communications at all. 

In a typical example a DL in Germany had a schedule with a VK in
Australia. The DL accessed easily and heard his own signal clearly ,
but heard nothing of the VK. While the VK heard the DL only very
weakly and spasmodically, far below a level suitable for
communications. The problem is fading of the signal which appears to
occur 3 times each spin revolution of the satellite, ie as the
triangular points of the satellite body perhaps, obscure the line of
sight between the satellite omni antenna and the ground station. In
practice the depth of this fading depends on the aspect of the
satellite as seen from the ground station. Where a station in one
hemisphere has a good view of the antenna, a station in the other
hemisphere has little or no view of the antenna. For stations in the
same hemisphere but on different continents , the signals are
stronger, and while the same 3 fades per spin rev are present, they
hinder but do not prevent communication. Eg DL to W is a typical case
where this has been happening.

BUT, this situation is changing at this moment to something even less
predictable as Oscar Ten's spin rate gets slower and slower. In Jan 96
it was 2.2 rpm. In Aug 96 it was 2 rpm. In Jan 97 it was 1.5 rpm and
it is now in Jan 98 0.16 rpm. ( These spin figures assume that one
revolution produces 3 dips in signal as each corner of the satellite
temporarily obscures the whole or part of the omni antenna.).

That Oscar Ten has virtuallly stopped spinning is perhaps bourne out
by the fact that the 3 signal peaks per satellite revolution are no
longer the same strength and duration. A feature which may suggest
that as the satellite spun down , it is now slowly tumbling around at
least 2 axes, rather than spinning firmly around one. What will happen
next is anyones guess. The satellite may now tumble in an increasingly
irregular fashion, or, it may even start to spin up in the opposite
direction to that which it followed previously. Time will tell.

Caution . We cannot read Oscar Ten telemetry, and we cannot climb a
ladder and observe it visually. The above assumptions are based on
observations of satellite signal to noise, and , orbit location versus
station location data. IHJ will gladly listen to anyone who thinks he
has a better interpretation of these observations.

Chronological List title - Oscar Ten . No Spin ?
Suggested Index reference - AO10 Oscar 10