The Active CryoCubeSat Project: System Modeling and Control Design

Utah State University together with the NASA Jet Propulsion Laboratory have been developing new cooling technology for high power CubeSats. This effort has been funded by the NASA Space Technology Mission Directorate in an effort to enable CubeSats with extraordinary thermal control needs for subsystems such as computing, telemetry, or cryogenics and where passive techniques are insufficient. The approach is to use a pumped fluid loop to remove heat from an internal heat exchanger and transport it to an external radiator on the CubeSat. Recently, Utah State has thermal vacuum-tested prototype systems collecting significant amounts of data on the thermodynamics of pumped fluid loops for small spacecraft. This paper presents the model-based thermal feedback and control system design for Utah State’s Active CryoCubeSat prototype. This system is based on a single-phase, two-stage mechanically pumped fluid system, designed to support 6U CubeSat platforms and above. The system modeling was conducted using two different approaches. First, a physical model was derived from the first principle equations, then a system identification was conducted using data collected from the thermal vacuum chamber test of the ACCS system. This paper presents the results and comparison of both models, as well as their limitations in describing the physical behavior of the system. Based on those models, a control system was designed and tuned to achieve a series of thermal requirements for the thermal control of a small cryocooler supporting an infra-red detector at 70 to 120K