Multi-disciplinary optimization of the low-thrust orbit raising for the hydroterra Earth Explorer mission

Hydroterra was selected in September 2018 as one of the three candidates for the ESA's Earth Explorer-10 mission. Hydroterra aims at observing and improving the understanding of fundamental processes of daily water cycle, enhancing prediction capability of extreme rainfall and related flooding. To achieve this goal, the mission concept envisages placing a satellite embarking a synthetic aperture radar instrument in geosynchronous orbit. The satellite is designed to be launched with VEGA-C into low Earth orbit and to be transferred to the operational orbit by means of electric propulsion. In this paper, the multidisciplinary optimization process carried out to obtain the baseline electric orbit raising transfer for Hydroterra will be presented. The computed trajectory will meet the mission requirements, including targeting to the operational orbit, the launcher per-formance model, and the target on-station mass. Additionally, system-level constraints related to the satellite design that have an influence on the ideally optimized trajectory will be derived and considered in the opti-mization. In particular, the impact of the solar cell degradation on the thrust and specific impulse levels of the thruster due to the passage through the Van-Allen belts, the need to re-charge the batteries before entering the next eclipse, and the agility requirements will be accounted for. The obtained results show that a feasible electric orbit raising trajectory can be successfully obtained for the Hydroterra mission.