Simulations of cold-gas nozzle and plume flows and flight data comparisons

The nozzle and plume flows of small cold-gas attitude control thrusters, pl ume interactions with spacecraft surfaces, and the induced pressure environ ment are investigated numerically. The motivation for this study originates from pressure measurements that exhibited nonperiodic pulses during the fi rings of small cold-gas thrusters onboard a suborbital spacecraft. Pitch, y aw, and roll cold-gas thrusters were located on the 0.56-m-diam base of the spacecraft. The conical spacecraft flew at altitudes between 670 and 1200 km and carried inside a pressure sensor connected to the side surface with a tube. Predictions of the pressure inside the sensor chamber are obtained using a semi-analytical model with inputs from coupled continuum and kineti c simulations. The nozzle and plume flows for each thruster are simulated u sing a three-dimensional Navier-Stokes solver until breakdown. Flowfield pr operties inside the breakdown surface are used as inputs to the direct simu lation Monte Carlo calculations in a domain that includes the spacecraft ge ometry. Flowfield properties at the entrance of the sensor tube are used as inputs to an analytical model to obtain the pressure inside the sensor cha mber. Simulations show plume expansion, reflection off the spacecraft surfa ces, and backflow Pressure predictions for the pitch and yaw thruster plume s that reach the sensor after expanding on the spacecraft base are in very good agreement with measurements. Pressure induced by the roll thrusters is shown to be very sensitive to their radial position at the Environmental M onitor Package base and decreases with decreasing radial distance. Pressure overprediction of the roll thrusters is attributed to possible difference between the simulated and actual radial position.