Determination of the accelerometer metrological characteristics on board the METRIC mission

METRIC is a proposed mission that aims to improve the knowledge of atmospheric density, general relativity and geodesy. The mission foresees a small spherical satellite placed in a polar eccentric orbit, with the apogee at 1200 km of altitude and perigee at 400–450 km. The spacecraft will be tracked from ground and space and have an on-board 3-axis accelerometer. The accelerometer will measure non-gravitational accelerations (due mainly to neutral drag and solar radiation pressure). A dynamical simulator has been implemented with known models (e.g. higher-harmonics gravity field, upper atmosphere density, solar pressure) in order to estimate the non-gravitational accelerations acting on the satellite. These are then analyzed in order to extract their main characteristics: intensity and frequency spectrum. Consequently, an envelope for the accelerometer features - dynamic range, required accuracy and frequency bandwidth - can be set. The data collected by the accelerometer will be used, in combination with tracking data from GNSS and SLR, to improve the atmospheric density knowledge over a wide range of altitudes, to perform an accurate measurement of the orbital precessions predicted by general relativity and implement a space-based tie of geodetic reference frames.