For a number of applications in oceanography, hydrology, glaciology and
the solid Earth sciences, the mapping of the Earth’s global gravity field can provide
a critical observational and constraint dataset. The GRACE mission, selected under
the NASA Earth System Science Pathfinder (ESSP) program for a mid-2001 launch,
will provide a major advancement in the mapping of the Earth’ s gravity field in both
the mean sense and for temporal variations on time scales of 30 days and longer.
This mission will provide measurements of the range between two low Earth
orbiters to submicron precision using dual-one-way, dual frequency microwave
tracking. The two orbiters will be placed in near polar, near 500 km altitude orbits,
separated from each other by approximately 250 km, over a mission lifespan of 3-5
years. The satellites will also carry GPS receivers and high precision accelerometers
to aid the recovery of the gravity field from observational data. In our oral
presentation, we provided a summary status of the project to date. Also, we reviewed
the science rationale and capabilities of GRACE for the measurement and
monitoring of the Earth gravity field changes. The impact of the result from GRACE
on our measurement and understanding of global climate change, and its interaction
with other space and ground-based geophysical data sets were discussed.