Mission concepts for the Superconducting Gravity Gradiometer

Abstract

The Superconducting Gravity Gradiometer (SGG), which can measure gravitational field fluctuations to unprecedented precisions, is currently being evaluated for use in an Earth-orbiting platform. Two missions are planned: a Shuttle-based demonstration flight and a dedicated gravity surveying mission. The Shuttle mission will feature a fully functional, self-contained instrument with an intrinsic noise level of 10 −3 E Hz −1 2 , where E is defined at 10 −9m s −2 m −1. Calibration hardware, residual error correction techniques, and surface tension devices which control liquid helium motion in the dewar will be tested. For a dedicated free-flier gravity mission, two concepts have been studied. Both have been formulated to achieve low cost while maintaining an instrument sensitivity of 10 −3 E Hz −1 2 . One concept uses the spacecraft developed for the Sub-millimeter Wave Astronomical Satellite (SWAS), and would be in a polar orbit, decaying from an initial altitude of 380 km. A mission lifetime of 6–9 months is planned. The other concept is based on a re-usable SPARTAN 400 carrier which would be deployed from, and retrieved by, the Shuttle. The carrier can be periodically reboosted and would maintain an altitude between 275 and 350 km. The mission lifetime is restricted to about 3 months, and the orbit inclination is limited to 57 °, the maximum the Shuttle can reach. Since the carrier is retrieved, the instrument could be periodially reflown. The free-flier missions, including experiment and spacecraft design, are described.