Tests of general relativity in earth orbit using a superconducting gravity gradiometer

Abstract

According to general relativity, the gravitational field is fully described by the Riemann curvature tensor. The Riemann tensor near the Earth has two components, one arising from the mass of the Earth (Schwarzschild term) and the other from the angular momentum of the Earth (Lense-Thirring term). A sensitive three-axis superconducting gravity gradiometer in a polar orbit could detect both of these terms. Two interesting space experiments are discussed in this paper. First, the tracelessness of the Riemann tensor, which represents a relativistic generalization of the inverse square law, could be tested by summing the three outputs of the gradiometer. This experiment would also constitute a very sensitive search for a new feeble force. Second, the Lense-Thirring term, which is caused by the gravitational analog of the magnetic field, could be separated from the large Newtonian background by its frequency characteristic and its unique symmetry property. We discuss the principles of these experiments, and derive the instrument, spacecraft, and orbit requirements imposed by such experiments.