| Summary: | The purpose of this research has been to develop a technique by which satellite
constellations in different classes of orbit may be realistically compared. Previous work on
constellation design has tended to focus on minimising the number of satellites required to
provide coverage of the Earth. The variations in satellite vehicle design, which result from
the use of different orbits, have, in general, been neglected in such analyses. The purpose of
this research is to bridge this gap between constellation design and satellite design using a
Figure of Merit.
This Figure of Merit incorporates the coverage value provided by the satellite
constellation, measured in terms of percentage coverage time, and the overall mass of the
satellites which are required to provide this coverage.
The coverage value is measured against a specific requirement, which is defined
geographically, and which may be weighted by the user to reflect the relative importance of
different regions. This allows arbitrary, asymmetric, real-world requirements to be
adequately represented. This also marks something of a departure from previous work, in
that the goal of much constellation design work has been to provide un-weighted coverage of
the entire globe.
Simplified mass models are developed for generic communications and surveillance
satellites in a variety of orbits, and are then used to calculate the Figure of Merit for
individual satellites.
It is shown that the best solution depends crucially upon the geographical distribution
of the requirement, and other user-defined parameters, such as the minimum elevation angle
which can be tolerated. It is also shown that, for certain typical requirements, the Figure of
Merit correctly identifies geostationary orbit (GEO) and low Earth orbit (LEO) as having
particular advantages.
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The technique of characterising the requirement geographically may also be used as a
means of optimising the orbital parameters of the candidate constellations, and a preliminary
description of this procedure is also provided.
The Figure of Merit Technique is then applied to representative communications
satellite constellations in order to demonstrate its ability to differentiate between candidate
options.
The Figure of Merit technique is also used to investigate the possibility of using a
surveillance satellite at very low altitudes.
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