Determination of the Earth's Gravitational Field Parameters Based on Inter-satellite Measurements between Cubesate-type Nanosatellites

Design of a space gravitational gradiometer for creation of Earth's gravimetric maps for navigation is proposed in the paper. The operation principle of the gravitational gradiometer is to measure the inter-satellite distance, which changes due to different impact of the earth's gravitational field on the gravitational gradiometer's spacecrafts. It is proposed to measure the inter-satellite distance increments using a Michelson laser interferometer. Different configurations of space gravitational gradiometer for the case of passive reflectors and active signal retranslation are considered. The maximum possible intersatellite distance between satellites at which optical interferometric measurements with passive reflectors can be performed is estimated. A universal structural optical scheme of the laser interferometer for both active and passive satellite configurations is proposed. The main nodes of the laser interferometer are considered: stabilized laser source, optical guidance system and photodetector registration system. The main sources of noise in the proposed interferometer are considered: frequency instability of the laser source and optical frequency retransmission system; angular noise of the pointing system; temperature noise and photodetector noise. The estimation of the noise budget and the contribution of each noise source to the measurement accuracy is given. At the total noise level of about 10-20 pm, the measurement accuracy of the gravitational field gradient is 10
^-7
Eotvos.