Application of orbital aerodynamics to satellite attitude control

UoM administered thesis: Phd

  • Authors:
  • Sabrina Livadiotti

Abstract

Very low Earth orbits (VLEO) with altitudes below 450 km are generally avoided for most applications. At such low altitudes, aerodynamic forces become the most significant source of attitude and orbit perturbation, whilst gravity gradient and residual magnetic dipole torques increase due to proximity with the Earth. In this scenario, the question of whether novel aerodynamic control strategies can be used to facilitate attitude and orbit control tasks arises. This thesis documents novel control methods that take advantage of aerodynamic torques to perform: 1) combined aerodynamic and reaction wheels pointing, 2) three-axis aerodynamic control and 3) reaction wheels momentum management below 300 km. A comprehensive review of the uncertainties associated with space weather and the mechanisms of interaction of the particles with the satellite is performed. These uncertainties are taken into account in the design of a novel real-time algorithm to determine the configuration of some control surfaces inducing the desired aerodynamic control torques. A representative 3U CubeSat with four motorised surfaces is then taken as reference to explore feasibility of the three control methods proposed. The analysis of the results benefits from the implementation of a realistic simulation environment, which allows to reproduce the inaccuracies affecting performance at the state of the art. A Monte Carlo analysis is also included to demonstrate the controller robustness against the identified sources of uncertainty and, more importantly, to acknowledge its limits. Comparison with results obtained in the presence of materials promoting quasi-specular reflection is presented with the purpose of discussing possible future developments. The analysis of the results show that active aerodynamic control is feasible and that the proposed control solutions, despite their relative simplicity, are robust enough to assure the control tasks completion under uncertain and highly variable orbit conditions. In particular, performance at altitudes lower than 250 km demonstrate that active aerodynamic control represents a cost-effective alternative to more conventional techniques and that it can be conveniently employed in presence of relaxed requirements. The proposed control algorithms are adapted to the very limited attitude hardware and software specifications of SOAR (Satellite for Orbital Aerodynamics Research), which is due to be launched in 2021 within the frame of the DISCOVERER project. The algorithms are implemented on SOAR’s on-board computer (OBC) with the aim of performing the first on-orbit demonstration of active aerodynamic attitude control in VLEO. Integration and validation of the aerodynamic control algorithms on SOAR’s OBC are discussed in details. The performance expected to be achievable under the specific uncertainties associated with the platform design are finally addressed.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date31 Dec 2021