Development of Superconducting Gravity Gradiometers

Precise gravity measurements are required to study the fundamental nature of gravitation.  Measurements of gravity can also provide a better understanding of the Earth and the planets, help find natural resources, and improve inertial navigation and surveying.  To distinguish gravity from platform accelerations, the Equivalence Principle requires a differential measurement.  A gravity gradiometer detects a spatial derivative of the gravitational field and ideally is immune to the vibrations of the platform.

Several versions of the superconducting gravity gradiometer (SGG) have been developed.  A three-axis in-line component SGG, developed with NASA support, has reached a performance level of 2*10^-11s^-2Hz^-1/2in the laboratory.  The achieved common-mode rejection of 10⁷ is sufficient for a spacecraft environment.  However, for terrestrial moving-base applications, the linear acceleration rejection must be improved to 10⁹ or higher. 

A cross-component device can be designed to be inherently insensitive to linear accelerations by employing pivoted moment arms whose mass moments are precisely balanced prior to assembly.  We have developed such a device and demonstrated a sensitivity of less than 10^-9 s^-2 over a bandwidth of 0.001 to 2 Hz. This gradiometer is described in a Rev. of Sci. Inst. paper.