-- Starting tomorrow (3/15), two new Earth-orbiting satellites will bear witness to the fact that even a force as relentless as gravity can prove fickle. Ohio State scientists are helping NASA and the German Geodetic Center prepare for GRACE, the Gravity Recovery and Climate Experiment, which will map tiny changes in the Earth's gravity. The results could help scientists better understand global climate change.

Ocean currents, the flow of molten rock, the melting of glaciers -- all nudge the force of gravity slightly higher or lower in localized spots around the world every day, explained C.K. Shum and Christopher Jekeli, both professors of civil and environmental engineering and geodetic science.

Shum and Jekeli are devising complex physical principles and techniques for understanding the new gravity measurements GRACE will obtain. For instance, the data could help explain how underground aquifers and melting glaciers affect global sea levels. GRACE is also expected to provide revolutionary measurements for monitoring the movement of groundwater, which could improve flood prediction worldwide, Shum said.

The project -- the first of NASA's Earth System Science Pathfinder small satellite missions -- is run by scientists at the University of Texas Center for Space Research. The twin GRACE satellites will circle the globe in tandem, effectively drawing a picture of the Earth's gravity field once a month for five years. Onboard instruments will measure very precisely any minute tugs the Earth exerts on the satellites while they're in orbit. Shum and Jekeli will use that information in their climate change research.

A new German-Russian joint venture company called Eurockot Launch Services will launch the satellites from the Plesetsk Cosmodrome, a facility some 400 miles northeast of St. Petersburg, Russia. This mission marks the first commercial operation for Eurockot, as well as the first commercial use of a Russian ICBM, or intercontinental ballistic missile. The re-tooled ICBM was the only rocket large and powerful enough to launch both GRACE satellites at once.

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