Six-Degree-of-Freedom Analysis of CubeSat Flight Performance in Very Low Earth Orbits

Abstract

Aerodynamic forces significantly affect spacecraft operating in very low Earth orbits, especially CubeSats with limited control authority. Six-degree-of-freedom analysis is required to assess the impact of aerodynamic forces on attitude and translational motion for missions operating in this flight regime. In this work, the flight performance of a range of CubeSats is compared in the context of a high-altitude atmospheric probe mission based on metrics, including detumble time, total mission lifetime, stabilizing time, and duration of time spent in a stable orientation. Three different attitude determination and control systems are considered: magnetorquers with a partial vehicle state available from magnetometers, magnetorquers with a full vehicle state available, and reaction wheels with a full vehicle state available. Flight performance is assessed over multiple mission parameters of interest, including the total available control authority, the initial apoapsis, the duty cycle, and the ability to accommodate quiescent periods for science data collection. Results indicate that a vehicle equipped with magnetometers and magnetorquers using a Bcross detumble algorithm throughout the mission provides limited performance and may not be acceptable for some missions, although performance improves as the orbit decays and atmospheric density increases. Further, although reaction wheels are capable of providing asymptotic stability around the desired vehicle attitude, magnetorquers are able to provide similar performance, provided a full vehicle state is available onboard.