High-fidelity Optimal Control Laws to Characterize the Maneuvering Capabilities of Earth-bound Solar Sails

Abstract

Solar sailing is a propulsion method that uses solar radiation pressure (SRP) as main source of thrust and is therefore particularly suited for heliocentric flight regimes. However, the vast majority of sailcraft launched to date have flown around Earth, as will those scheduled for launch in the near future. Around the Earth, the dynamics of a solar sail are affected by the presence of eclipses and additional sources of acceleration apart from SRP, in particular, atmospheric drag and the Earth’s planetary radiation pressure (PRP). These accelerations can reach magnitudes in the order of (or even larger than) the SRP acceleration and, therefore, they can potentially be exploited to manoeuvre more effectively around the Earth. Nevertheless, the majority of research conducted on Earth-bound solar sailing either neglects these accelerations or treats them as uncontrollable sources of perturbation. In light of this, this paper presents a high-fidelity trajectory optimisation method which is then used to thoroughly characterise the manoeuvring capabilities of solar sails in the near-Earth environment. The optimisation algorithm is designed to change any orbital element in a locally optimal manner while accounting for the SRP, PRP, aerodynamic, and gravitational accelerations. To tune the optimiser, a first-order analysis of the accelerations achievable by sailcraft in proximity of the Earth is discussed. Then, the optimisation algorithm is exploited to fully characterise the manoeuvring capabilities of Earth-bound solar sails, taking NASA’s recently-launched ACS3 solar-sail mission as a baseline. Specifically, different parametric analyses are conducted to determine ACS3’s orbit-raising and inclination-changing capabilities for a large set of orbits, solar activities, and sailcraft characteristics. The results of this study not only enhance the understanding of ACS3’s performance but also provide valuable insights for the mission design of future Earth-bound solar-sail missions for a variety of mission applications, such as active-debris removal and in-orbit servicing.