UBC Theses and Dissertations
Reduction of Earth observation system response time using relay satellite constellations Sanad, Ibrahim Shaaban
System Response Time (SRT) is the interval between submitting an imaging request to, and receiving imagery from, Earth Observation (EO) satellites. Reduction of SRT is especially important in natural disaster and national security situations. The use of dedicated relay communication satellite constellations (RCSCs) to significantly reduce SRT has long been recognized but often dismissed as too costly. In recent years, however, the introduction of low-cost satellite and launcher technology has rekindled interest in this approach. Here, we contribute tools, techniques, and insights that allow designers to design RCSCs for EO constellations more systematically than previously possible. First, we present a framework for designing RCSCs in support of EO constellations based on the industry-standard System Tool Kit (STK) software and demonstrate its use. Second, based on a statistical analysis of the orbital parameters for 34 remote sensing satellite constellations (RSSCs) and a thorough review of their missions, we propose nine representative classes that allow the performance of RCSCs to be broadly assessed with far less effort than testing against an exhaustive set. Third, we present a toolkit for calculating SRT for various relay network configurations and implement it as STK add-on modules. We also present a tool to design RCSCs in Medium Earth Orbit (MEO) that can achieve persistent inter-relay intersatellite links (ISLs) and thereby minimize SRT. Fourth, for cases where the RCSCs have persistent inter-relay ISLs, we use our tools to generate performance curves that show how system response is affected by changes in the orbital altitudes and inclinations of the relays, and the latitude of a ground station and thereby overcome a key limitation of previous work. We demonstrate that a Walker-Delta 4/2/1 RCSC with 4 satellites in two planes achieves much better performance at a much lower cost than a Walker-Delta 3/3/0 RCSC with 3 satellites in three planes when serviced by a single ground station. This is noteworthy given that Walker-Delta 3/3/0 configuration will be used by the recently announced first commercial MEO relay satellite constellation. The results convincingly demonstrate the value of assessing the sensitivity of a given relay constellation to its design parameters.
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