This paper discusses the scientific motivation for, design of and buildup of the Spatial heterodyne Spectrometer (SHS) for a sounding rocket mission to study the Cygnus Loop, a prototypical middle-ages supernova remnant. The results of that mission are also presented. The goal of the flight was to obtain a radial velocity-resolved spectrum of the C IV (lambda) 1550 emission line from the Cygnus Loop, as a test for doing the same from the diffuse hot interstellar medium (ISM). The reasons for wanting to look at the ISM this way are discussed, along with the properties of SHS. Important points about alignment (zero-path and zero-spatial-frequency setting), as well as shake testing and data analysis techniques (fringe correction, thermal drift tracking) are described. The SHS payload did not obtain a spectrum for th Cygnus Loop C IV emission line, because of reduced efficiency of the optical components. Results of post- flight efficiency tests to locate the source(s) of this loss are presented, showing contamination as the most likely problem. Ways to eliminate this contamination for future SHS sounding rocket and satellite missions conclude the presentation.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.