REMOTE MEASUREMENT SYSTEM FOR ARC JET TEMPERATURE AND DENSITY

THE PROPERTIES OF THE SHOCK-CREATED PLASMA CREATED DURING ATMOSPHERIC RE-ENTRY (WHICH CAN BE SIMULATED IN THE LABORATORY USING AN ARC JET FLOW) MUST BE KNOWN TO CONTROL THE PROBLEM OF SPACECRAFT HEATING, BOTH DIRECTLY AND BY HOT GAS TRANSPORT TO THE REAR OF THE VEHICLE. WE WILL INVESTIGATE THE USE OF LASER-INDUCED FLOURESCENCE (LIF) TO OBTAIN DETAILED INFORMATION ABOUT THESE PROPERTIES. THIS TECHNIQUE HAS SEVERAL ADVANTAGES OVER THE EXISTING TECHNIQUES OF EMISSION SPECTROSCOPY, CALORIMETRY, AND RADIOMETRY. THE ABSOLUTE NUMBER DENSITIES AND TRANSLATIONALTEMPERATURES OF OXYGEN AND NITROGEN ATOMS CAN BE DIRECTLY MEASURED, WHICH SHOULD IMPROVE PREDICTIONS OF SPACECRAFT HEATING BY SURFACE RECOMBINATION. VIBRATIONAL AND ROTATIONAL TEMPERATURES FOR MINOR COMPONENTS OF THE FLOW, WHICH SHOULD SERVE AS "THERMOMETERS" FOR THE OVERALL ENERGY DISTRIBUTION WITHIN THE FLOW, CAN BE DIRECTLY MEASURED. THE LIF TECHNIQUE IS VERY SENSITIVE, IS FLEXIBLE ENOUGH TO BE USED ON MANY DIFFERENT SPECIES, AND CAN MAKE MULTIPLE SPECIES MEASUREMENTS (OR TEMPERATURE MEASUREMENTS ON A SINGLE SPECIES) INSTANTANEOUSLY. AFTER CHOOSING THE OPTIMUMLIF SCHEME, WE WILL DESIGN A PROTOTYPE LASER-BASED DETECTIONSYSTEM, WHICH WILL BE CONSTRUCTED AND CALIBRATED IN A PHASE II EFFORT, AND EVENTUALLY INSTALLED AND OPERATED ON AN APPROPRIATE NASA ARC-JET FACILITY.