Jim Faller is working on the final analysis of a precise determination of the Newtonian gravitational constant (G) and the acceleration of gravity (g). To measure G, mirrors are embedded in the bobs of two pendulums, forming a Fabry-Perot interferometer. He measures G by placing large tungsten source masses between the pendulums. Then, he moves the tungsten masses, which pull the bobs apart. He repeats this sequence every two minutes. By using frequency methods to precisely measure the spacing, the gravitational force on the bobs can be determined. Faller has also developed a new instrument for measuring g. This device is small, portable, and uses a mechanical cam system to release, catch, and lift a corner-cube-containing mass whose free-fall behavior can then be studied. This compact instrument should facilitate a multitude of field and laboratory measurement applications.

Precision measurement in geophysics is being planned from space. Peter Bender is working with colleagues at the University of Colorado and Ball Aerospace on designing and testing a laser interferometer system for measuring changes in the distance between three spacecraft engaged in mapping Earth's gravity field. The system will make precise measurements of distance changes between carefully shielded test masses inside drag-free spacecraft (roughly 50 km apart) over periods ranging from 10 to 100 seconds. The project is part of a feasibility study for a follow-on mission to the Gravity Recovery and Climate Experiment (GRACE) mission, which is currently mapping Earth's gravity field.