METRIC: a mission based on Italian technology for upper atmosphere mapping, gravitational physics and geodesy

We propose and investigate the concept of a spacecraft to be placed in a low Earth orbit (LEO), with dedicated instrumentation to provide data useful for upper atmosphere mapping, fundamental physics and geodesy. These three areas, distinct but at the same time strongly interrelated in the case of Earth system science, can benefit from the availability of a well-calibrated space-based platform such as the one being here proposed. The proposed mission, named METRIC (Measurement of EnvironmenTal and Relativistic In-orbit preCessions), features three main scientific objectives: 1) Map the upper atmosphere density by in-situ acceleration measurement and by spacecraft tracking, at altitudes of great interest for satellites deorbiting and, in general, for probing the neutral atmosphere in an altitude range not covered by current thermospheric density models; 2) Perform fundamental physics tests through a Precise Orbit Determination (POD) and consequent verification of the relativistic equation of motion for a well-characterized test mass; 3) Provide an additional, space-based node to improve the tie among different space geodesy techniques. These objectives could be achieved through a satellite in LEO equipped with a dedicated set of instrumentation, including a high-sensitivity accelerometer, a vacuum pressure ion-gauge and the equipment allowing its tracking by two or more space geodetic techniques. The data produced by the on-board instrumentation and the ground segment will allow at the same time a verification of the relativistic equation of motion and an additional tie among Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS), with a possible, optional inclusion of Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS).