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RAgeo, a low cost GEO bird



There are a couple of issues with putting a satellite into GEO without fuel
:-

1) If the inclination drifts, the satellite is not GEO - it becomes
Geo-Synchronous, i.e. it appears in the same position in the sky at one
particular time every day; at other times it will 'move' due to the
lattitude of the sub-satellite point varying with the orbit.  However, for
low inclinations, and with wide beamwidth antennas, this will not be a
problem.

2) Another reason why GEO comms sats carry so much fuel (which is a major
cost factor) is the fact that the earth's gravitional field is not connstant
around the equator - there are bulges, or 'hills' and 'valleys'.  If a
satellite was left in Geostationary orbit, with the inclination staying at 0
degrees, with no orbital corrections, the satellite would drift around the
equator.  For example, a satellite above the Atlantic would drift east (I
think) until it reaches the Indian Ocean, where it will stay.  And this is
what happens to communications and broadcast satellites when they 'retire' -
they end up in a different part of the sky, being of some use to Asian
broadcasters etc. who get to use a funtional satellite whose orbit cannot
easily be controlled.

I'm not sure how long it would take for any satellite to 'drift' across the
equator, but it would be a factor that would need to be considered.


regards

Grant Hodgson
G8UBN@amsat.org
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