Mission scenarios and system architecture concepts for a Next Generation Gravity Mission

Alberto Anselmi(1), Stefano Cesare(1), Miguel Aguirre(2)
(1) Thales Alenia Space Italia, Torino, Italy
(2) ESA-ESTEC, The Netherlands

Since 2003, the European Space Agency has promoted assessment studies and technology developments in preparation of a future space gravity mission based on the Satellite-to-Satellite Tracking technique with laser metrology. Thales Alenia Space Italia has led three of these studies in which, in particular, different mission scenarios and mission architectures have been investigated, a first measurement error budget has been established and a preliminary top-down requirements allocation to the satellite elements has been performed.

The simplest mission scenario capable to potentially achieve the required amplitude resolution in the gravity field temporal variation monitoring consists of two satellites flying along the same sun-synchronous, circular orbit at 10 km relative distance and 325 km mean altitude for at least 6 years. In this scenario, a payload (laser metrology and accelerometers) capable to measure the inter-satellite distance with an error spectral density , and the non gravitational accelerations on the satellites with an error spectral density , will in theory enable the determination of the geoid height variation with an error = 0.1 mm/year at .

Since this basic mission scenario still does not meet the objectives of improving the temporal resolution in the gravity field temporal variation monitoring and the separability of the geophysical signals, more complex scenarios have been assessed. They consists essentially in flying more satellite pairs on orbits with different inclinations and/or adopting different formation geometries (e.g. cartwheel, pendulum-type). Any of these deviations from the basic scenario has important implications on the satellite configuration, the payload instruments, the formation, drag-free and attitude control system, the mission operations, and thus on the complexity and cost of the mission. Therefore a careful trade-off between the scientific return and the “affordability&lrquo; of each scenario is mandatory for identifying the best way of implementing such Next Generation Gravity Mission.