UCLA

Predicting and managing heat transfer during planetary entry is a critical engineering challenge for current and future space exploration missions. This work aims to improve the understanding of thermodynamic non-equilibrium during Mars entry via experimental studies to capture chemical kinetics and the rates of energy transfer between translation, rotation, and vibration for the dominant molecular species (CO2 and CO). The key elements of this research can be split into two distinct phases: (1) develop and demonstrate non-equilibrium high speed sensing of CO and CO2 on a high enthalpy shock tube at UCLA. (2) Deploy the sensor at NASA Ames on a representative Mars entry flow. A mid-infrared laser absorption strategy for simultaneous measurement of translational, rotational, and vibrational temperatures of carbon monoxide (CO) at high speeds was developed for application to high temperature non-equilibrium environments relevant to Mars atmospheric entry. The sensing strategy is shown to resolve each targeted transition with temporal and spectral resolution sufficient for quantitative multi-temperature measurements over a wide range of temperatures and pressures (2100 - 5500 K, 0.03 - 1.02 atm), including behind incident shock waves traveling up to 3.3 km/s. A similar strategy is employed on CO2 transitions from the ν3(00^00) and ν3(01^10) states. Vibrational relaxation times were resolved at temperatures relevant to Mars backshell heating (2,000 - 3,000 K) in various CO2 - Ar mixtures and found to be in good agreement with the Simpson rate model. The final effort of this project deployed a multi-species sensor on the Electric Arc Shock Tube facility at NASA Ames to study a recreated shock layer similar to that experienced on the Mars2020 mission. Temperature and number densities of CO2 and CO were extracted from the data and compared to various chemistry models and a simultaneous emission measurement. At shock velocities below 3.1 km/s, the agreement between the measurements and the Johnston mechanism is typically within 5\% for temperature and within 10\% for number density. At shock velocities above 3.1 km/s, the CO2 measurement becomes sensitive to a thin boundary layer and corrections of this effect are presented. On test cases with enough energy to dissociate CO2, a quantum cascade laser scanned the P(2, 20), P(0, 31), and P(3, 14) transitions of the CO fundamental band at 4.98~�m. CO formation rate is measured to be close to the Johnston kinetic mechanism at low velocities, and then trending towards the Cruden kinetic mechanism at high velocities. In summary, this work has advanced laser absorption techniques to include high speed (MHz) multi-temperature measurements of CO2 and CO on non-equilibrium flows relevant to Mars planetary entry.