Mission design aspects for the mass change and geoscience international constellation (MAGIC)

The Mass Change and Geoscience International Constellation (MAGIC) is planned as the first realization of a double-pair low-low satellite-to-satellite (ll-sst) tracking gravity mission consisting of a polar and an inclined satellite pair. Due to the much increased spatial and temporal resolution and multidirectionality of the data to be collected by this mission, new possibilities regarding the resolvability of mass transport processes in space and time are expected. In order to maximize the scientific and societal outcome of this mission, an optimization of both the mission design as well as the methods to process the expected data is fundamental. Using numerical closed-loop simulations, we investigate the impact of several key mission design aspects on the gravity retrieval from a double-pair constellation such as the planned MAGIC mission. Specifically, we show how the choice of the second pair's inclination poses a trade-off between a reduction of retrieval errors at latitudes covered by data from both pairs and at higher latitudes, thereby requiring a compromise between the latitude-dependent accuracy requirements of different user groups. One of the key mission goals is to provide fast-track gravity products with short latency for operational service applications. Towards the estimation of such short-term gravity fields of a few days, we investigate if coordinating the polar and inclined pairs' orbits to achieve a stable ground-track coverage is necessary for obtaining a homogeneous accuracy of subsequent gravity solutions. Indeed, combining two freely drifting, uncontrolled orbits significantly degrades short-term gravity fields in time periods in which both pairs show coinciding ground track gaps. Finally, we analyse the relative performance of the two satellite pairs. Double-pair scenarios that are strongly dominated by the inclined pair's data reveal degraded gravity solutions when co-estimating daily gravity fields as de-aliasing strategy. This effect can be mitigated by choosing a more balanced double-pair configuration, for example by choosing similar orbit heights and instrument noise levels for both satellite pairs. The findings presented in our study will serve to optimize the system design of the upcoming MAGIC constellation.