Development of a Photonically Generated Frequency Reference for Space VLBI

Abstract: Space-based Very Long Baseline Interferometry (VLBI) can improve both the angular and temporal resolution of images over terrestrial VLBI techniques. Future space VLBI (sVLBI) missions are targeting higher observation frequencies than modern, terrestrial VLBI, and therefore these missions will require higher stability frequency references than standard hydrogen masers. While existing frequency references for space-based applications have concentrated on long-term stability, in this effort, we present a frequency reference with high short-term stability intended for sVLBI missions. This reference leverages developments in cavity-stabilized lasers from the Laser Interferometer Space Antenna (LISA) mission and commercial efforts towards a robust, space-qualifiable optical frequency comb. We describe the implementation and experimental results of this system with a path to spaceflight, which demonstrates an Allan deviation of $3.26 \times 10<sup>{-14}$ at 1 second, $6.00 \times 10<sup>{-15}$ at 10 seconds, and $6.73 \times 10<sup>{-15}$ at 30 seconds for the 100 MHz frequency reference signal, and show that this performance meets the needs of future sVLBI missions.