Title: Laser Frequency Stabilization for GRACE-2
Primary Author: Folkner, William
Organization: Jet Propulsion Laboratory
Co-Author(s): W. M. Folkner, G. deVine, S. Esterhuizen, W. M. Klipstein, K. McKenzie, D. Shaddock, R. Spero, R. Thompson, D. Wuchenich, N. Yu - Jet Propulsion Laboratory, California Institute of Technology
M. Stephens, J. Leitch, M. Davis, J. deCino, C. Pace, R. Pierce - Ball Aerospace and Technologies Corporation

Abstract:
The GRACE mission monitors changes in the Earthís gravity field by measuring changes in the distance between spacecraft induced by that changing field. The distance variation is measured with a microwave ranging system with sub-micron accuracy. The ranging measurement accuracy is limited by the signal-to-noise ratio and by the frequency stability of the microwave signal referenced to an ultra-stable oscillator (USO). For GRACE-2 a laser ranging system is envisioned with accuracy better than the GRACE microwave ranging system. A laser ranging system easily provides improved signal-to-noise ratio over the microwave system. Laser frequency stability better than the GRACE USO stability has been demonstrated in several laboratories using thermally stabilized optical cavities. We are developing a space-qualifiable optical cavity and associated optics and electronics for use on GRACE-2 to provide a stable frequency reference for the laser ranging system. Two breadboard units have been developed and tested for performance and ability to survive launch and orbit environments. A prototype unit is being designed using lessons learned from test of the breadboard units.