Minimum Transfer Times for Nonperfectly Reflecting Solar Sailcraft

Abstract

Introduction S OLAR sailcraft trajectory analyses are typically made for highperformance sailcraft under the assumption that the solar sail is either an ideal reflector or by consideration of the nonideal reflectivity through an overall efficiency factor that reduces the magnitude of the solar radiation pressure (SRP) force but leaves its direction unaltered.1−3 In both cases, the SRP force model is a model of perfect, that is, specular, reflection because the direction of the SRP force is always perpendicular to the sail surface. For a thorough mission analysis, however, one must consider the optical properties of the real nonperfectly reflecting sail film, where the SRP force also has a component parallel to the sail surface. Taking the current stateof-the-art in engineering of ultralightweight structures into account, solar sailcraft of the first generation will be of relatively moderate performance. The simplification of perfect reflectivity and the limitation on high-performance sailcraft seem both to be caused mainly by the difficulty of generation of an adequate initial guess for traditional local trajectory optimization methods. As a smart method for global trajectory optimization, artificial neural networks can be combined with evolutionary algorithms to form so-called evolutionary neurocontrollers (ENCs).4 Evolutionary neurocontrol (ENC) does not require an initial guess. By the use of ENC, near globally optimal trajectories can also be calculated for nonperfectly reflecting solar sailcraft of moderate performance. In the sequel, after the different SRP force models have been defined, minimal transfer times for rendezvous missions within the inner solar system will be presented for perfectly and nonperfectly reflecting solar sailcraft, including a near-Earth asteroid rendezvous (1996FG3) and a main belt asteroid rendezvous (Vesta).