The StarLight metrology subsystem

We describe a metrology subsystem for NASA's StarLight mission, a space-based separated-spacecraft stellar interferometer. It consists of dual-target linear metrology, based on a heterodyne interferometer with carrier phase modulation, and angular metrology designed to sense the pointing of the laser beam. The dual-target operation enables one metrology beam to sense displacement of two targets independently. We present the current design, breadboard implementation of the metrology subsystem in a stellar interferometer testbed and the present state of development of flight qualifiable subsystem components.