FLEX: A Parametric Study of Its Tandem Formation With Sentinel-3

The Fluorescence Explorer (FLEX) is an Earth observation mission currently in development by the European Space Agency to perform quantitative measurements of the solar induce vegetation fluorescence. As a core of the mission concept, FLEX is planned to be launched by the end of 2023 and shall fly in tandem with one of the Copernicus Sentinel-3 satellites, which is already in orbit. This situation will allow FLEX to benefit from the optical and thermal sensors of Sentinel-3 and provide an integrated package of measurements. This paper presents the preliminary parametric analysis on the along-track dynamic of the tandem flight formation between Sentinel-3 and FLEX. It includes the study of the maneuvering strategy for a master-slave scenario concept, where Sentinel-3 acts as the master of the formation, whereas FLEX is the slave. This control strategy is assessed in terms of safety for both satellites and performance, where it is of interest to maintain the along-track distance between satellites as bounded as possible. Numerical and analytical results of this paper are provided showing that the control strategy proposed is able to fulfill the mission requirements under the expected conditions while providing enough time for the control center to coordinate the orbital maneuvers of Sentinel-3 and FLEX. Additionally, and from the results obtained in this paper, it is concluded that the safest configuration for the mission is locating FLEX ahead of Sentinel-3.