Strategies for Optical Measurements in Rocket Plumes

An ideal rocket engine sensing system might probe several key elements of the rocket engine including: the fuel and oxidizer supply for mass flow rate and impurities, the combustion chamber for pressure and mole fraction of reactants, or the plume for temperature and mole fraction of products. This thesis focuses on the rocket plume component of a rocket engine sensing system. The rocket plume sensor consists of a wavelength scanning laser that spatially sweeps through the rocket plume in order to determine the temperature, water mole fraction, and pressure at different positions in an axially symmetric plume. Because of the low absorbance that will occur in a small rocket plume (<1% for a 2 inch diameter plume), all noise must be minimized. The three largest sources of noise are mode noise, beamsteering, and laser intensity noise. Throughout this research, these three sources of noise are studied in depth. Final recommendations are given for designing a system that will successfully measure these qualities in a rocket plume.