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Geodesy and Gravity Experiment in Earth Orbit Using a Superconducting Gravity Gradiometer

A superconducting gravity gradiometer is under development with NASA support for space application. It is planned that a sensitive three-axis gravity gradiometer will be flown in a low-altitude (~ 160-km) polar orbit in the 1990's for the purpose of obtaining a highresolution gravity map of the Earth. The large twice-an-orbit term in the harmonic expansion of gravity coming from the oblateness of the Earth can be analyzed to obtain a precision test of the inverse square law at a 100 ~ 1000-km distance. In this paper, we describe the design, operating principle, and performance of the superconducting gravity gradiometer. We discuss the concept of a gravity-gradiometer mission (GGM), which is in an initial stage of development. In particular, requirements that such a mission imposes on the design of the cryogenic spacecraft will be addressed.