GRACE, twin satellites (launched in March 2002) is making detailed measurements of Earth's gravity field. Analyses of data from GRACE have led to important discoveries about gravity and Earth's natural systems, which in turn have far-reaching benefits to society and the worlds's population.
Data from GRACE are providing scientists with a globally consistent measurement of the distribution of Earth's mass and its variability in time and space. This variability in mass is due primarily to water motion. Thus, measurements from GRACE provide an internal constraint on many geophysical processes related to land, ocean, atmosphere and glaciological systems. A record of time variations in Earth's gravity field reflects the redistribution and exchange of mass within and between these reservoirs. Over one-quarter of the world's population relies on groundwater as its principal source of drinking water.
GRACE-II will extend and improve on the first GRACE mission. Resolution would be increased to around 100 kilometers. Accuracy could be boosted by development of a laser-based satellite-to-satellite interferometer and a drag-free propulsion system, with boosters continually fired to minimize orbital degradation caused by atmospheric drag. The resulting data will foster major breakthroughs in a number of areas of Earth science.