Global gravity survey by an orbiting gravity gradiometer

Abstract

Three dedicated space missions proposed for the 1990s promise to provide data for recovering the Earth's gravity anomaly with unprecedented accuracy and resolution: the Geopotential Research Mission (GRM), the Aristoteles Mission, and the Superconducting Gravity Gradiometer Mission (SGGM). SGGM, the most ambitious of the three, aims at recovering the global gravity field to a precision of 2–3 mGal with a resolution of 50 km. Such accuracy and resolution are required to answer many key questions in geophysics. The SGGM instrument package is a three‐axis superconducting gravity gradiometer which is integrated with a six‐axis superconducting accelerometer and a six‐axis shaker for active platform control. The intrinsic sensitivity of the gradiometer is 10−4 E Hz−½ (where E represents the unit of gravity gradient (1 E = 1 Eötvös = 10−9 s−2)) and that of the accelerometer is 10−13 gE Hz −½ in linear acceleration and 10−11 rad s−2 Hz−½ in angular acceleration. While precise attitude control of the Experiment Module is essential to mission success and is also technically the most challenging, pointing accuracy and disturbance isolation requirements of SGGM are less stringent compared to that of other missions such as the Hubble Space Telescope (HST) and Gravity Probe‐B (GP‐B). Thus they are within the reach of technologies of the 1990s. In the recently completed Phase A study, the SGGM Study Team addressed the problem of scientific requirements and mission feasibility. Marshall Space Flight Center is continuing with mission and spacecraft design, while mission simulation is being done at Goddard Space Flight Center, Greenbelt, Md. At the University of Maryland, prototypes of the three‐axis gradiometer and the six‐axis accelerometer are being fabricated, improved, and tested. A Shuttle flight test of the Experiment Module with the actual instrument package is suggested for 1994–1995. The full science mission hopefully will take place before the year 2000.

Gravity, Gradiometry

“…Besides the Hughes RGG (which did not fly on a satellite), a major effort was undertaken by NASA to put a superconducting gravity gradiometer (SGG) into low Earth orbit in the 1980s. The SGG was developed by the University of Maryland (Moody et al 1986;Paik et al 1988) as an outgrowth of the technology for highly sensitive gravity wave detectors. Based on accelerometers that use the magnetic flux exclusion principle of superconducting bodies, the SGG was designed primarily to sense the in-line gradients.…”

STAGES OF DEVELOPMENT AND STATE OF ENGINEERING OF GRAVITY GRADIOMETERS FOR MOVING OBJECTS. (Review)

“…Начало этой работы положило NАSА, которое поставило задачу создания методов и устройств изучения гравитационного поля Земли на низкоорбитальных спутниках, а также гравитационных полей других небесных тел (см. [1][2][3][4], [5 и имеющиеся там литературные ссылки]). Подобные устройства незаменимы при исследованиях внутреннего строения Луны и планет, где измерения силы тяжести с борта орбитальных аппаратов в принципе невозможны.…”

Gravity field determination and characteristics: Retrospective and prospective

“…Satellite gravimetry works only with gravity gradiometers (satellite-to-satellite tracking being a special case), and two systems were specifically developed for such an application. Taking advantages of the low thermal noise of cryogenic instrumentation, H. J. Paik of the University of Maryland constructed a gravity gradiometer based on SQUID (Superconducting Quantum Interference Device) technology, with a theoretical gradient sensitivity approaching 10 '4 EU in the zero-G environment of space [Paik et al, 1988]. For airborne applications this instrument has the potential of very useful sensitivity estimated at 10-1 EU.…”