Analysis of pressure measurements during cold-gas thruster firings onboardsuborbital spacecraft

Pressure measurements taken onboard a suborbital spacecraft exhibit nonperi odic pulses during attitude control thruster firings. The attitude control system located at the base of the conical spacecraft Included eight cold ga s thrusters. The pitch and yaw thrusters delivered 1.245 N thrust while the roll thrusters delivered 3.278 N with impulses that lasted up to 0.03 s. T he pressure sensor was housed inside the spacecraft on a plane 0.15 m from its base and was connected to the outside with a 0.1 m long, 0.022-m-diam t ube. Analysis shows that pressure pulses appear instantaneously with firing s although the thrusters did not have a direct line of sight with the senso r entrance. Pressure pulses are superimposed on a background pressure that is attributed to internal outgassing, Plumes from thrusters with the same l evel of thrust result in large differences in pressure depending on their o rientation with respect to the entrance of the pressure sensor tube. Data a nalysis demonstrates that outgassing, plume backflow, and plume/surface int eraction affect the neutral pressure environment of the small suborbital ve hicle.