Intersatellite laser ranging instrument for the GRACE follow-on mission

The Gravity Recovery and Climate Experiment (GRACE) has demonstrated that low–low satellite-tosatellite tracking enables monitoring the time variations of the Earth’s gravity field on a global scale, in particular those caused by mass-transport within the hydrosphere. Due to the importance of long-term continued monitoring of the variations of the Earth’s gravitational field and the limited lifetime of GRACE, a follow-on mission is currently planned to be launched in 2017. In order to minimise risk and the time to launch, the follow-on mission will be basically a rebuild of GRACE with microwave ranging as the primary instrument for measuring changes of the intersatellite distance. Laser interferometry has been proposed as a method to achieve improved ranging precision for future GRACE-like missions and is therefore foreseen to be included as demonstrator experiment in the follow-on mission now under development. This paper presents the top-level architecture of an B. S. Sheard (B) · G. Heinzel · K. Danzmann Max Planck Institute for Gravitational Physics (Albert Einstein Institute) and Institute for Gravitational Physics, Leibniz Universität Hannover, Callinstrasse 38, 30167 Hanover, Germany e-mail: [email protected] G. Heinzel e-mail: [email protected] K. Danzmann e-mail: [email protected] D. A. Shaddock Department of Quantum Science, The Australian National University, Building 38a, Science Rd., Acton, ACT 0200, Australia e-mail: [email protected] W. M. Klipstein · W. M. Folkner Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA interferometric laser ranging system designed to demonstrate the technology which can also operate in parallel with the microwave ranging system of the GRACE follow-on mission.