Next Generation Gravity Mission Elements of the Mass Change and Geoscience International Constellation: From Orbit Selection to Instrument and Mission Design

ESA’s Next Generation Gravity Mission (NGGM) is a candidate Mission of Opportunity for ESA–NASA cooperation in the frame of the Mass Change and Geosciences International Constellation (MAGIC). The mission aims at enabling long-term monitoring of the temporal variations of Earth’s gravity field at relatively high temporal (down to 3 days) and increased spatial resolutions (up to 100 km) at longer time intervals. This implies also that time series of GRACE and GRACE-FO can be extended towards a climate series. Such variations carry information about mass change induced by the water cycle and the related mass exchange among atmosphere, oceans, cryosphere, land and solid Earth and will complete our picture of global and climate change. The main observable is the variation of the distance between two satellites measured by a ranging instrument. This is complemented by accelerometers that measure the nongravitational accelerations, which need to be reduced from ranging measurements to obtain the gravity signal. The preferred satellite constellation comprises one satellite pair in a near-polar and another in an inclined circular orbit. The paper focuses on the orbit selection methods for optimizing the spatial sampling for multiple temporal resolutions and then on the methodology for deriving the engineering requirements for the space segment, together with a discussion on the main mission parameters.

An Optimal Selection Model of the Satellite Lurk Orbit

An optimal selection model of the lurk orbit on which a satellite will park waiting for instructions aiming at a non-cooperative space target is presented. The model uses factors including orbit maneuver satisfaction degree in special cases and orbit utilization value in ordinary uses taking into account orbit maintenance cost, orbit availability and the resulting elusiveness. These factors are derived from dynamics characteristics of the space target orbit and the optional lurk orbits. The model is employed to select the optimal lurk orbit from several optional orbits for a satellite taking aim at a non-cooperative space target so as to secure ordinary utilization and effective respond when receiving instruction to perform tasks concerning the space target. In the presented work, lurk orbit selection processes in an application example are analyzed using the model. It is seen that the optimal selection model effectively solves lurk orbit selection