Emission spectroscopy is a powerful non-intrusive research tool for investigating combustion processes. This technology is being researched and transitioned into rocket engine ground test operations at Stennis Space Center (SSC). Much has been achieved with commercially available emission spectrometers and much more is expected from the next generation equipment, such as the Optical Plume Anomaly Detector (OPAD) emission spectrometer designed specifically for this purpose. Some basic issues are being researched at SSC to make exhaust plume diagnostics a fully operational tool for propulsion system ground test operations. Knowledge gained during the development of this technology for ground test is critical to the development of flight-rated sensors and for Vehicle Health Management System(s) (VHMS) for future vehicles, such as the New Launch System (NLS), National Aerospace Plane (NASP), and those developed for the Space Exploration Initiative (SEI).