Baseline metrology system of the U.S. Naval Observatory Astrometric Interferometer

The USNO Astrometric Interferometer (USNOAI; the dedicated subarray of the Navy Prototype Optical Interferometer at Lowell Observatory, Flagstaff, AZ) is presently under construction and expected to begin limited operations in the spring of 1993. The main goal of the USNOAI observations is to provide a northern hemisphere catalog of approximately a thousand stars with positions known to a few mas. In order to meet this requirement, a baseline laser metrology system must be employed to measure the 3D motions of the baselines with an accuracy better than approximately equals 0.1 micrometers . The metrology scheme, as presently conceived, represents the largest and most complex high-resolution laser metrology system ever attempted.