Design, Manufacturing, and Testing of a Cold Gas Thruster System With Minimized Actuators

Cold gas thrusters are commonly used on spacecraft for in-space attitude control and adjustment. These thrusters use inert gases stored at high pressures to create small amounts of thrust and typically have multiple fixed outlets, each controlled by its own actuated valve, to control the direction the thrust is directed. Having individual outlets with their own actuated valve leads to a great amount of power drawn for the individual actuators, as well as general added complexity by having a large number of parts. To address this issue, this thesis investigates an attempt to minimize the number of actuators required for a cold gas thruster system to operate. This thesis details the design, analysis, electronics integration, manufacturing, and testing of a cold gas thruster system with as few actuators as possible. In addition, a thrust target, a maximum response time, and a long duration test regime were set as requirements to drive the design. From these goals and requirements, a cold gas thruster system that uses a single central selector valve to control the actuation of four outlets while only using two motors was designed. The selector valve design uses a sleeve that rotates and moves vertically to align ports in the valve to allow the propellant gas to flow freely through the valve and to the nozzle where thrust is produced. The sleeve is rotated by a motor connected to a pair of gears, and the vertical motion is controlled by a motor with a lead screw. Along with the mechanical design of the system, a great amount of compressible flow fluids analysis was performed. This analysis was used to determine the geometry of the outlet nozzle and its tolerances. In addition, a model was created using MATLAB and Simulink to predict the pressure drops throughout the system. This model is used to estimate the necessary pressure regulator outlet pressure that produces the nominal thrust. The electronic control panel was developed to control the motors as well as to obtain performance data. Stepper motors were used to control the selector valve and controlled by a Teensy microcontroller board and custom libraries to operate the stepper motors simultaneously. Pressure and thrust data were collected from sensors that report the data to an Arduino microcontroller. The testing performed was highly successful with the thrust requirement and the long duration test regime requirements were achieved, while the maximum response time requirement was missed, but not by a large margin. The targeted thrust was able to be produced, and the required endurance test profile was successfully performed. The response time requirement was met for two out of the three valve actuation motions and was slightly exceeded for the last one.