Small Relay Satellite(s) for Improving the Reactivity of Observation Satellites

Abstract

The study is about a low cost data relay satellites solution, for upgrading the reactivity of earth observation (civil and military) and scientific satellites, in the next decades, and its comparison with a totally ground solution obtained by appropriate number and location of ground stations. A cooperative exploitation of all the earth observation satellites available in Europe after 2010 will provide a good flying frequency capacity over a same site (less than 3h). But this performance, very expensive to achieve because directly linked to the number of satellites, may not be fully exploited because of lack of communication links (scheduling and image data return) and in particular in case of operation theatre. In that case, the following global loop should be minimized : images data return from one satellite, data interpretation, scheduling preparation and telecommand of the following satellite. So the reactivity need is translated in emergency data return need and emergency scheduling need. After this reactivity need analysis, several relay satellites scenario are studied and traded, according to different parameters: the intersatellite links type : RF or optical : the orbit (Medium or geostationary Earth Orbit)), the interest zone (Europe or global earth), the satellite size (micro-satellite, mini-satellite ,else, passenger payload). The relay payload mass is relatively small (#60 kg). The RF option focuses the difficulty on the required antenna size (#2m) for Ka band return link and the S band two ways scheduling link , which leads to study dedicated small satellite solutions. Optical option enables smaller payload and piggybacking approaches provided that the scheduling is also done in the optical spectrum at price of some operational constraints like rendez-vous procedure with LEO (Low Earth Orbit) satellite not required with the S band. .For the terminal on the LEO satellite, the situation is opposite with optical bringing higher accommodation constraints. Other trade-off analysis, like the terminal complexity, lead to recommend interruption of LEO imaging mission during the image return link, which of course bring the interruption duration (typically few minutes per 10 Gbits) within the key performance criterias. A technical (including design and levels of performance) and economic analysis (including development, launch and replacement policy) allow to compare all the satellites solutions and those based on ground stations network.