Design and attitude control of a spinning octaSail solar sailcraft

Abstract

Solar sailing has gained a huge interest in the area of spacecraft propulsion. The tradional propulsion techniques such as chemical propulsion are not suitable for long-term interplanetary mission applications. This is evident from the mankind’s success so far as it has still not reached the farthest possible edges of solar system. The primary limitation for such interplanetary missions is the capability to carry enough chemical fuel that may ensure the mission operation for a longer mission life. Solar sailing is being considered as a potential replacement to the existing propulsion techniques especially for the cases of interplanetary mission operations. This is due to the infinite delta-v provision of this technology that may enable a solar sailcraft to travel away from the Sun at an acceleration much faster compared to the chemical propulsion based spacecrafts. A solar sailcraft is a spacecraft that consists of a large membrane upon which the radiation of the sun acts as a propulsion force. The incident photons on the large membrane area get reflected from the membrane surface and produce a solar thrust that accelerates the sailcraft. The resultant acceleration depends upon a number of factors such as the incident solar radiation pressure, the area of the membrane, and the direction of the solar radiation incident on the membrane of the sailcraft. Almost a hundred years of theoretical and practical efforts by theorists, researchers and developers have led to a number of successes recently in the area of solar sailing. Most of these developments occurred in the last decade with the realization of actual solar sailcraft missions such as NanoSail-D, LightSail-1 and IKAROS. The success of IKAROS has proved to be a source of great momentum in the research related to solar sailcraft technology. This success has led to the consideration of in-depth research in the area of more solar sailcraft designs such as OctaSail, the subject of this thesis research. Based on the in-depth study of existing research literature, it is concluded that the performance of any sailcraft depends upon a number of factors that include the design configuration of the sailcraft, the material being used in the membrane, the method to deploy the sailcraft membrane, and the method to ensure the flatness of the membrane. These factors together lead to a baseline characteristic that can be used to evaluate the performance of any sailcraft and this baseline characteristic is known as Characteristic Acceleration. Based on the detailed qualitative and quantitative analysis, a spinning octagonal configuration consisting of eight tip masses is proposed and is termed as OctaSail. OctaSail is a spinning sailcraft that offers an extended area of the membrane while keeping the length of tip-mass attachment strings same as those in the case of IKAROS. Similarly, a membrane area equal to IKAROS is possible to be achieved with smaller lengths of tip mass attachment strings compared to those used in IKAROS. The detailed research has shown that the OctaSail design is capable of out-performing other sailcraft designs due to its better characteristic acceleration. In this research, the design of this OctaSail has been discussed and presented in detail. Moreover, the most challenging aspect of a spinning sailcraft is its attitude control. The attitude behavior of the OctaSail without using reflection control devices, and the attitude control of OctaSail by using reflection control devices is also discussed. Finally, feedback based attitude control logic is implemented to consider the uncertainties in system modeling.