A Preliminary Availability Assessment of A LEO Satellite Constellation

This paper presents a preliminary assessment of operational availability of a LEO satellite constellation with a single orbital plane. A new model is developed. Unlike traditional availability models developed from using Markov chains, this model derives expected service downtimes from probability distributions directly, due to the unrepairable nature of a failed satellite on orbit. Two types of service downtimes are considered: one attributed to redistributing remaining satellites to restore full coverage of the orbit if there are spare satellites still available, and the other attributed to a partial loss of the orbital coverage due to a permanent gap created by an additional satellite failure if there is no spare available. This model establishes a baseline for validation and verification of any numerical assessment tool to be developed in the future for complex LEO satellite constellations with multiple orbital planes, due to the fact that the single orbital plane constellation is a special case of complex constellations by setting the number of orbital planes equal to one and the analysis results obtained from the tool with such setting should be identical or close to the ones obtained from the analytical model presented here. An example is presented. And a proposed path-forward to develop a comprehensive LEO satellite availability assessment tool is outlined at the end of the paper.