Passive Attitude Stabilization of CubeSats in Low Earth Orbit

Abstract

CubeSats are miniatured spacecraft that are designed for space exploration and experimentation at low mission cost as compared to conventional satellites. In general, CubeSats require stabilization about at least one of their axes to perform certain mission objectives. The attitude of a CubeSat can be controlled either through power-consuming active control strategies or by passive control strategies that require no or low power. Implementation of passive control strategies can reduce the overall cost of mission development by eliminating the use of expensive active control actuators. Hence, enhancing the performance of the satellite and accommodating secondary mission objectives. The main aim of this study is to successfully develop, simulate, and verify an effective approach to passively control CubeSat attitude by modifying the geometrical design and mass distribution taking into account the environmental disturbances experienced by the satellite. This way, we are reducing the reliance on control actuators. As a result, improving the survivability and maximizing the benefits that can be attained from a mission. The tool developed in this research consists of an orbital and attitude propagator comprising of all external disturbance torques. The developed tool was successfully validated against the results of literature and those obtained from available software, wherever possible. One of the main findings from the conducted analysis is that hysteresis torque is the only environmental disturbance torque that causes significant damping of the satellite's angular rate. Furthermore, it was found that all disturbance torques decrease when considering higher altitudes except for the solar radiation torque that is independent to the changes in altitude. Magnetic and gravity gradient torque decreases linearly whereas, aerodynamic torque decreases exponentially as a function of increase in altitude. The effect of aerodynamic torque becomes negligible beyond 700 km altitude. At LEO, the most significant torques include gravity gradient, magnetic, and aerodynamic torque. Several passive stabilization techniques were considered in this study. Among the proposed passive stabilized designs, the most effective one was passive magnetic stabilization that comprises ALNICO-5 permanent magnet along the primary axis and HyMu-80 hysteresis material along the two secondary axes. Based on this design, the satellite became aligned with the earth magnetic field within 50 minutes and it was then stabilized to below 10° error angle with earth magnetic field in 2.5 hours. Other two passive control designs were also considered. These are based on the gravity gradient and aerodynamic stabilization. In both the designs, the satellite achieved the required alignment; however, taking more time as compared to passive magnetic stabilization and with higher error angle to nadir or velocity vector direction.

Date of Award	Dec 2021
Original language	American English