ESA's Studies of Next Generation Gravity Mission Concepts for Monitoring Mass Transport in the Earth System
Massotti, Luca; Siemes, Christian; Di Cara, Davina; del Amo, Jose Gonzalez; Girouart, Benedicte; Roger, Haagmans; Silvestrin, Pierluigi
The paper addresses the preparatory studies of future ESA mission concepts devoted to improve our understanding of the Earth’s mass transport phenomena causing temporal variations in the gravity field, at different temporal and spatial scales, due to ice sheet and glaciers melting trends, continental water cycles, ocean masses dynamics and solid-earth deformations. The ESA initiatives, started in 2003 with a study on observation techniques for solid Earth missions, continued recently through several system studies and technology developments, either for propulsion, e.g. tests on miniaturized ion thruster , or distance metrology, e.g. laser interferometry. These activities received precious inputs from the in-flight lesson learnt from ESA's Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission and the American-German Gravity Recovery and Climate Experiment (GRACE) mission.
The "Assessment of a Next Generation Gravity Mission to Monitor the Variations of the Earth's Gravity Field" (concisely: NGGM) was performed in two parallel studies, one led by Thales Alenia Space (Turin, Italy) and another one by Astrium GmbH (Friedrichshafen, Germany). Both consortia included European universities and academic institutions for scientific support and requirement assessments. Several mission aspects were analyzed, leading to different mission concept features. The preferred mission concepts fitting the defined programmatic boundary conditions have been studied with prioritized science requirements and detailed system designs. In addition to the drivers due to tight propulsion requirements and accelerometer calibration issues, representing a dominant error source at large scales, the technical constraints on power and fuel generally dictate the choice of orbit. Thus, for each considered constellation type, the different interactions between drag-free and "loose" formation control have been analyzed together with the design of the relative attitude control that is necessary to ensure the inter-satellite laser link all along the mission length.
Since then, several complementary and TRP (Basic Technology Research Programme) studies were initiated and are currently running, notably:
The latest results concerning the preferred satellite architectures and constellations, payload design and estimated science performance will be presented as well as remaining open issues for future concepts. Attention will also be given to the ongoing ESA-NASA inter-agency cooperation to align preparatory work on synergistic mission concepts beyond GRACE Follow-On.