Аннотация:The goal of the project is the construction of a wideband gravitational gradiometer based on a laser 100-m Fabry-Perot-Michelson interferometer on free masses in deep rock surroundings. The device is aimed at registering bursts of gravitational radiation with an amplitude of the dimensionless metric variations as small as 10-21 in the frequency range 102-103 Hz. The auxilliary purpose is to measure low-frequency variations of the Earth gravity gradients bearing information on the internal dynamics of our planet. The deep under-rock position of the installation inside tunnels of Baksan Neutrino Observatory provides a two-order of magnitude decrease in the geophysical noise level which allows the combination of parallel astrophysical and geophysical studies. For geophysics, the long-based interferometer with hanging mirrors presents a new type of geophysical instrument - an angular gravity gradiometer at low frequencies 10-4-10-5 Hz with a resolution of 10-8-10-10 rad, which is enough to register weak geodynamical perturbations due to oscillations of the Earth interiors.