As part of the SFB geo-Q, in collaboration with the Albert Einstein Institute (AEI), we are investigating aspects for a future laser-interferometric inter-satellite ranging mission for space-based measurements of the gravitational field of the Earth and its fluctuations.
This project consists of studying potential mission concepts, including the performance analysis and experimental investigations of the intersatellite laser link and its acquisition.
The overall ranging noise of a GRACE-type mission consists of many contributions that depend partially on the properties of individual subsystems (like the laser stability), and very often also on properties of the satellite and constellation as a whole. For the GRACE Follow-On Laser Ranging Instrument (LRI) with its 80 nm/√Hz noise level, it is known that the most important contributions to the noise budget are due to laser frequency noise and satellite pointing jitter. In order to achieve 10 nm/√Hz for future missions, improvements in many areas are necessary, such as the pointing stability, which can be improved if interferometric signals are used. In this project the capabilities and constraints of the individual subsystems of the interferometer are being studied.
In addition, together with our colleagues at AEI, we have set up various experiments involving laser interferometery and precision measurements to test various critical components and functionalities that will be key for a successful mission, such as the initial link acquisition, and components related to the transponding of the laser signal and local optical benches.
While many aspects can be studied by computer simulations, the most reliable and informative test is an experiment, which constitutes a major part of this project. The output of this part will be robust acquisition procedures tested by simulation and experiment, and a flexible testbed that allows testing of alternative procedures as well as testing of flight-like hardware.