ELECTRIC-FIELD AND RADIO-FREQUENCY MEASUREMENTS FOR ROCKET ENGINE HEALTH MONITORING APPLICATIONS

Widespread efforts are being conducted toward development of real-time health-monitoring systems for the Space Shuttle main engine (SSME). Electric field (EF) and radio frequency (RF) emissions generated in the exhaust plumes of the diagnostic testbed facility thruster (DTFT) and the SSME on the A-1 test stand at the John C. Stennis Space Center have been examined briefly for potential applications to plume diagnostics and engine health monitoring. The exhaust plume of the SSME (and DTFT) is a high-velocity, cool plasma with ions accelerating at various rates. The exhaust produces electromagnetic radiation, whose temporal and spatial characteristics vary with engine operating parameters. Hypothetically, anomalous engine conditions could produce measurable changes in any characteristic EF and RF spectral signatures identifiable with a "healthy" plume. Tests to determine the presence of EF and RF emissions in the DTFT and SSME exhaust plumes were conducted. EF and RF emissions were detected using state-of-the-art sensors. Analysis of limited data sets show some apparent consistencies in spectral signatures. Significant emissions increases were detected during controlled tests using dopants injected into the DTFT. The small data sets obtained were qualitative but not conclusive. Further data collection is required to establish repeatability and to identify emission sources accurately.