Satellite Constellations for Continuous and Early Warning Observation: A Correlation-Based Approach

Abstract

Recently, telecommunication and navigation corporations have shown a growing interest in low and medium Earth orbit constellations due to several operational advantages, such as reduced power requirements and signal time delays with respect to geostationary platforms. An increased imaging resolution of Earth's surface is also associated with the use of low orbits rather than high altitude orbits. A large set of parameters is involved in defining constellation configurations, so usually some basic assumptions are taken. For instance, this occurs for Walker constellations, exhibiting a high degree of symmetry and suitability for coverage of large areas. Yet, for special purposes, such as continuous observation or early warning monitoring of a specific location, geometric hypotheses often seem inadequate or oversimplified. In this paper all satellites are placed in circular, repeating orbits with semimajor axis and inclination yielding maximum visibility of a preselected target location. Then, a correlation function is introduced as an effective tool to find all allowed time delays between two consecutive passes over the target. Some optimal constellation configurations (of 2, 4, 8 satellites) are deduced and discussed with reference to different kinds of local observation.