SIM Brassboard Astrometric Beam Combiner ( ABC ) integration and performance testing

We discuss a brassboard implementation of the Astro metric Beam Combiner (ABC), a key element of the SI M Lite Astrometric Observatory (SIM). It combines starlig ht from the two SIM siderostats, detects starlight for angle tracking, and disperses and detects starlight for fringe trac king. The ABC also contains a stimulus, corner cube s and shutters for in-orbit calibration, tip/tilt mirror mechanisms fo r in-orbit alignment, and the internal metrology be am launcher. The design of the brassboard ABC, which has the form, f it and function of the flight unit, is complete. Su bassembly and bench-level integration is nearing completion, and functionality, performance, vibration and thermal t ests will follow.