The Skybridge Constellation Design

Abstract

The SkyBridge space segment, based upon Low Earth Orbit satellites, had to face a challenge: though using the same frequency band as various geostationary systems in order to profit by well-proven and cost-efficient techniques — i.e. Ku Band -, SkyBridge satellites must not in any way interfere with geostationary satellites. This “frequency sharing constraint” forces SkyBridge satellites to stop emitting (resp. receiving) towards (resp. from) any portion of the ground as soon as they are seen in alignment with the geostationary orbit from the point of view of this earth portion.

The paper focuses on how the coverage requirements, coupled with frequency sharing constraint, has led to a new original concept of satellite constellation design: in this concept, orbital planes are grouped by pairs, and within “double-planes”, satellites are also grouped by pairs. Thus, the whole 64 satellite constellation is in fact subdivided into two 32 satellite sub-constellations, and relative phasing between the two sub-constellations has been numerically optimised to provide the best coverage performance.

Space segment operational availability is also discussed: this figure of merit allows the constellation designer to build up an adequate maintenance strategy.