Consider the most fundamental difference between a solar sail and conventional spacecraft: propellant. In order to effect propulsion, solar sails receive a constant supply of massless photons to reflect while conventional spacecraft must carry a limited supply of fuel. At first glance, solar sails are infinitely more efficient than conventional spacecraft simply because of this fact. However, while certainly an advantage to solar sailing, propellant consumption is not the proper metric for spacecraft comparison or the only appealing facet of the solar sail.
It can be shown by a reasonable and straightforward analysis that solar sails have the potential to out-perform conventional spacecraft on the basis of effective specific impulse, a parameter that incorporates launch and payload masses as well as total mission duration via an adaptation of the illustrious rocket equation. Pair an aggressive specific impulse with the orbital possibilities that arise when solar sail performance is at a level capable of producing spacecraft accelerations the same order of magnitude as local solar or planetary gravitational acceleration, and the engineer finds significantly fewer constraints limiting the design of future space missions. Imagine a spacecraft for which a Lagrange equilibrium point becomes a large surface, rather than a singular location, on which it is able to remain at rest. Picture a space vehicle hovering high above an ecliptic plane or perhaps racing along some other non-Keplerian orbit taking measurements and relaying signals from positions previously untenable. Solar sails can do all of these things, and it is the intent of this body of work to generate a proof of concept for one of the most attainable and pertinent capabilities unique to solar sails mentioned thus far.
In the pages that follow it will be shown that a solar sail is inherently stable for some of the optimal non-Keplerian family of planet-centered orbits, and can be stabilized by straightforward control schemes for the rest. Beginning from scratch with a radiation pressure model, gain parameters were developed for low-impact and damped state feedback control via sail pitch attitude variation. Optimal orbits are attainable, as these trajectories were designed to minimize the required spacecraft acceleration and thus lower the solar sail performance requirement. Planet-centered orbits are pertinent, since a solar sail must inevitably begin its journey by escaping from the planet Earth and most of NASA’s recent efforts in space are geared towards the exploration of nearby planets and their moons. Uniqueness stems from the specification of the non-Keplerian family of orbits, since solar sails are capable of sustaining them whereas modern conventional spacecraft are not. In today’s day and age, with payload miniaturization and the ability to manufacture extremely light weight reflective materials, solar sailing has the potential to become reality within the next five to ten years. The concepts highlighted in this thesis have a significant probability of being among the first demonstrated capabilities of solar sail spacecraft once they take flight.