GLOBAL DESIGN OF SATELLITE CONSTELLATIONS - A MULTICRITERIA PERFORMANCE COMPARISON OF CLASSICAL WALKER PATTERNS AND NEW DESIGN PATTERNS

Basically, the problem of designing a multisatellite constellation exh ibits a lot of parameters with many possible combinations: total numbe r of satellites, orbital parameters of each individual satellite, numb er of orbital planes, number of satellites in each plane, spacings bet ween satellites of each plane, spacings between orbital planes, relati ve phasings between consecutive orbital planes. Hopefully, some author s have theoretically solved this complex problem under simplified assu mptions: the permanent (or continuous) coverage by a single and multip le satellites of the whole Earth and zonal areas has been entirely sol ved from a pure geometrical point of view. These solutions exhibit str ong symmetry properties (e.g. Walker, Ballard, Rider, Draim constellat ions): altitude and inclination are identical, orbital planes and sate llites are regularly spaced, etc. The problem with such constellations is their oversimplified and restricted geometrical assumption. In fac t, the evaluation function which is used implicitly only takes into ac count the point-to-point visibility between users and satellites and d oes not deal with very important constraints and considerations that b ecome mandatory when designing a real satellite system (e.g. robustnes s to satellite failures, total system cost, common view between satell ites and ground stations, service availability and satellite reliabili ty, launch and early operations phase, production constraints, etc.). An original and global methodology relying on a powerful optimization tool based on genetic algorithms has been developed at ALCATEL ESPACE. In this approach, symmetrical constellations can be used as initial c onditions of the optimization process together with specific evaluatio n functions. A multi-criteria performance analysis is conducted and pr esented here in a parametric way in order to identify and evaluate the main sensitive parameters. Quantitative results are given for three e xamples in the fields of navigation, telecommunication and multimedia satellite systems. In particular, a new design pattern with very effic ient properties in terms of robustness to satellite failures is presen ted and compared with classical Walker patterns. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.