Abstract: The invention relates to a communications and/or navigation system based on a constellation of non-geostationary satellites in orbit around the terrestrial globe. The constellation has satellites grouped in pairs, and has orbital planes that are also grouped in pairs. The pairs of orbital planes are mutually spaced apart by an angle that is different from the spacing between the orbital planes in a pair of orbital planes, and the satellites in a pair have orbital phase offsets different from the orbital phase offset between pairs of satellites in different pairs of orbital planes. This type of constellation makes it possible to ensure continuous coverage, via at least one satellite, of a geographical zone of interest, while taking into consideration the frequency-coordination constraint.

Abstract: The invention concerns, in particular, a system of observation of geostationary satellites (10.sub.1 -10.sub.n). In accordance with the invention, this system comprises at least one observation satellite (15) in an observation orbit (16, 17) near the geostationary orbit (11), this observation satellite (15) having an apparatus for observation of the geostationary satellites (10.sub.1 -10.sub.n) and an apparatus for transmission of the information obtained from the observation apparatus (20, 21, 22) to a receiver. The invention applies, in particular, to the discrimination of communication, meteorological, early warning and electromagnetic monitoring satellites.