Satgen305   Satellite Hindsight No4   by GM4IHJ                28 Jan 95
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One of the most noticable features of NASA operations has been their low
rate of failure, and it is highly likely that this has been due to their
firm policy of using only time and operational proven components. The
situation in Amsat has been somewhat different, with new ideas and designs
sometimes being tested for the first time in space, thereby tempting fate.
Eg going for a new design of amplifier which unhappily never worked in
space, or, in a second case, worked for a year or so then failed
completely.
Different again from NASA, Amsat tends not to review its failures, or
subject them to detailed public examination. Eg so far , at least 4
satellites using PSK modulation ( Phase Shift Keying ), have displayed
marked anomalies in keying. In some cases the actual Phase shift being far
removed from the designed 180 degrees. Thereby producing noisy, difficult
to demodulate, signals. But as this is being written several more PSK
systems are scheduled to launch or have just launched , with no one
suggesting that the problems of the first batch of 1990 PSK sats, have
been analysed and isolated, and, most important, corrected in subsequent
satellites.
A similar situation exists with respect to Phase 3 satellite antennas.
Because none of Amsats Phase 3 satellites has achieved a true Molniya
elliptical orbit, with consequent Molniya almost fixed earth pointing, the
2m antennas in particular have given poor results. In practice 2m antenna
polarisation has never achieved the fixed circular polarisation of the
original designs. Actual polarisation has varied from RH circular through
quasi elliptical polarisation all the way to polarisation in the opposite
direction LH circular, with actual polarisation depending on squint angle.
It is appreciated that the small size of the Oscar10 and 13 platforms
prevents really effective 2m antenna operation, but the problem has been
made far worse by not sticking to, or, achieving the true Molniya orbit.
This latter situation has arisen for a mixture of reasons , most notable
of which was the original Molniya conception when antennas were designed,
being changed very late in the launch sequence, to an orbit which provided
more useful Southern Hemisphere coverage. If Southern hemisphere coverage
was desirable, and this is not here contested, the antennas should have
been of totally different design. The question now before us is , will the
much bigger Phase 3 platform have more effective 2m antennas particularly
, noting that, it is not likely to go into a Molniya orbit. Equally
important will some means be found to prevent a repeat of the disturbing
spin modulation which plagues Oscar 13. 
It must be said at this time that though Amsat has never openly discussed
these problems, individual Amsat Officer have ceaselessly warned of the
difficulty of making any 2m system work effectively on a Phase 3
satellite. Indeed Phase 3D is carrying 2m equipment only because Amsat
members insisted on it . Hindsight in a few years time will probably
indicate that a 70 cm to 13 cm system will be the preferred Phase 3D mode.
In respect of these problems and others the guest editorial in Amsat
Journal Nov/Dec 94 makes interesting reading.
73 de GM4IHJ @ GB7SAN