The GOES Sounder is a 19-channel discrete filter radiometer. Studies by the University of Wisconsin and MIT Lincoln Laboratory indicate that retrieval performance could be improved y replacing the filter wheel with a Michelson interferometer. The interferometer system is to replace the relay optics and filter wheel and is required to use the existing GOES telescope and detector subsystems. Numerous configurations were considered in an effort to define a design which meets the optical specifications and fits within the limited available space with sufficient clearance around the optical components for the mechanical housings. The selected interferometer subsystem design fits within the available volume without rotation of the star sensor. Performance, diffraction and sensitivity analysis results are included.