Simulations of Cold-Gas Nozzle and Plume Flows and Flight Data Comparisons

Abstract

The nozzle and plume  ows of small cold-gas attitude control thrusters, plume interactions with spacecraft surfaces, and the induced pressure environment are investigated numerically. The motivation for this study originates from pressure measurements that exhibited nonperiodic pulses during the Ž rings of small cold-gas thrusters onboard a suborbital spacecraft. Pitch, yaw, and roll cold-gas thrusters were located on the 0.56-m-diam base of the spacecraft. The conical spacecraft  ew 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-analyticalmodel with inputs from coupled continuumand kinetic simulations.The nozzle and plume  ows for each thruster are simulated using a three-dimensional Navier–Stokes solver until breakdown. FlowŽ eld properties inside the breakdown surface are used as inputs to the direct simulationMonte Carlo calculations in a domain that includes the spacecraft geometry. FlowŽ eld properties at the entrance of the sensor tube are used as inputs to an analyticalmodel to obtain the pressure inside the sensor chamber. Simulationsshow plume expansion, re ection off the spacecraft surfaces, and back ow. Pressure predictions for the pitch and yaw thruster plumes 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 Monitor 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.