Design considerations for the USNO astrometric optical interferometer

The USNO will undertake the construction and operation of a phase coherent, astrometric, optical interferometer which will be dedicated to the determination of stellar positions and motions. Building upon the experience gained from the MARK III Interferometer at Mount Wilson, the USNO instrument is currently in the very early stages of conceptualization and initial design. An abbreviated account of the experience gained with the MARK III is given. Examples of the issues and possibilities to be addressed in designing the new USNO instrument are outlined. Some background discussion involving interferometric techniques is included.