Evaluation of Photodiode Arrays for Use in Rocket Plume Monitoring and Diagnostics

The spectroscopic analysis of plume emissions is a non-intrusive method which has been used to check for fatigue and possible damage throughout the pumps and other mechanisms in a rocket motor or engine. These components are made of various alloys. Knowing the composition of the alloys and for which parts they are used, one can potentially determine from the emissions in the plume which component is failing. Currently, Optical Multichannel Analyzer systems are being used which utilize charge coupled devices, cost tens of thousands of dollars, are somewhat delicate, and usually require cooling. We have developed two rugged instruments using less expensive linear photodiode arrays as detectors. A high resolution system was used to detect atomic emission lines while a low resolution system was used to detect molecular emission bands. We have also written data acquisition software and built electronic circuits to control the arrays and collect data. While NASA has used similar systems for characterization of the Space Shuttle Main Engine, the emissions from other rocket systems have not been surveyed as well. The two instruments described will be utilized to study hybrid rocket emissions at the UALR hybrid rocket facility