GRAS-F seismogravimeter for measuring gravity-inertial fields on the surface of Phobos
The problems of measuring the variations in the gravitational and inertial fields on Phobos related to librational oscillations, tidal effects, and seismic impacts have been considered in the paper. It has been indicated that thermal equilibrium noise in a mechanical oscillator, which forms the basis for a sensor, is responsible for the oscillator’s maximal sensitivity at a level of 8 × 10−9 m/s2. The actual sensitivity of the designed three-dimensional seismogravimeter, which was estimated based on the calibration results, is ∼2 × 10−8 m/s2. This makes it possible to measure the anticipated variations in the gravitational field and to obtain information about the seismic noise level with a surface oscillation amplitude resolution at a level of 2.5 × 10−7 m at frequencies of 0.1 Hz to ∼10−10 m at frequencies higher than 5 Hz.