Advanced Trajectories for Solar Sail Spacecraft

In this thesis the dynamics and applications of new advanced trajectories for solar sail spacecraft are investigated. By utilising the continuously available solar radiation pressure force exotic non-Keplerian trajectories which are unique to solar sail spacecraft are developed. Although large families of these new trajectories are found to be unstable, simple feedback control schemes are designed to ensure asymptotic stability. The unique nature of these trajectories opens up new space science mission opportunities, impossible for conventional spacecraft. These missions are shown to offer the possibility of interesting new observations of many aspects of solar system physics. In chapter 1 the concept of solar sailing is introduced and the history of its development reviewed. The fundamental design parameters for solar sail spacecraft are investigated and the fabrication of potential sail materials discussed. Square and heliogyro type solar sails are then described and their relative merits discussed. Modern state-of-the-art sail design and performance is then considered. Previous studies of solar sail mission applications are reviewed and recent concepts for future advanced applications discussed. The fundamental physics of solar radiation pressure is considered in chapter 2 along with the modelling of the solar radiation pressure force exerted on a real solar sail. Heliocentric solar sail trajectories are investigated and in particular the logarithmic spiral trajectory is derived. The limitations of such trajectories and the necessity of time optimal trajectories satisfying the two point boundary conditions of an interplanetary transfer trajectory are then indicated. The dynamics of geocentric escape trajectories are investigated and the use of optimised trajectories is again discussed. The solar radiation pressure model used in chapter 2 is expanded in chapter 3 to include astrophysical effects which have implications for solar sail dynamics. By the use of the radiation pressure tensor the effect of the finite angular size of the solar disk on the functional form of the solar radiation pressure force is obtained. The resulting deviation of the solar radiation pressure force from an inverse square variation with heliocentric distance is shown to have a de-stabilising effect on solar sails in stationary and circular orbital configurations. The effect of small time variations in the solar luminosity is also considered. In chapter 4 the first family of advanced solar sail trajectories is investigated. By obtaining stationary solutions to the heliocentric dynamical equations in a co-rotating reference frame the conditions for heliocentric halo orbits are obtained. These orbits are circular heliocentric orbits displaced out of the ecliptic plane by a component of the solar radiation pressure force exerted on the sail. Using a linear perturbation analysis the stability characteristics of the system are investigated and unstable families of trajectories found. Simple feedback control schemes are then obtained to ensure asymptotic stability. Lastly, by patching individual halo orbits and Keplerian orbits together, elaborate new patched trajectories are shown to exist. A similar analysis is used in chapter 5 to investigate geocentric halo orbits, which are near polar circular orbits displaced along the Sun-line by the solar radiation pressure force. Unstable families are again found with feedback control schemes developed to ensure asymptotic stability. The fundamental family of geocentric halo orbits is enlarged by the patching of individual halo orbits and Keplerlan orbits. In chapter 6 artificial stationary solutions to the circular restricted three-body problem are considered. The addition of the solar radiation pressure force leads to extensions of the five classical stationary points to a family of extended stationary surfaces. For the Earth-Sun system these new solutions are truly time independent. However, for the Earth-Moon system small trims in the sail area are required to compensate for the rotation of the Sun-line during the synodic lunar month. Again, the stability and control of the system is investigated and the instability of the solutions demonstrated. An out-of-plane trajectory at the lunar L2 point is also developed. The application of these new trajectories for potential space science missions is discussed in chapter 7. The scientific benefit of out-of-plane observations for solar system physics is explored and potential missions investigated. A simple, twin solar sail mission utilising heliocentric halo orbits is described. Similarly, the utilisation of geocentric halo orbits for geomagnetic tail observations is also investigated. Several applications of the new three-body stationary solutions are considered, such as the use of payload transfer from Lagrange point stationary surfaces to eliminate lengthy planetary spiral trajectories. Lastly, the conclusions of chapter 8 outline further possible developments in the areas of dynamics, control and mission analysis. Recommendations for the progress of advanced solar sail missions are given