RAPID SPACE TRAJECTORY GENERATION USING A FOURIER SERIES SHAPE-BASED APPROACH

With the insatiable curiosity of human beings to explore the universe and our solar system, it is essential to benefit from larger propulsion capabilities to execute efficient transfers and carry more scientific equipment. In the field of space trajectory optimization the fundamental advances in using low-thrust propulsion and exploiting the multi-body dynamics has played pivotal role in designing efficient space mission trajectories. The former provides larger cumulative momentum change in comparison with the conventional chemical propulsion whereas the latter results in almost ballistic trajectories with negligible amount of propellant. However, the problem of space trajectory design translates into an optimal control problem which is, in general, time-consuming and very difficult to solve. Therefore, the goal of the thesis is to address the above problem by developing a methodology to simplify and facilitate the process of finding initial low-thrust trajectories in both two-body and multi-body environments. This initial solution will not only provide mission designers with a better understanding of the problem and solution but also serves as a good initial guess for high-fidelity optimal control solvers and increases their convergence rate. Almost all of the high-fidelity solvers enjoy the existence of an initial guess that already satisfies the equations of motion and some of the most important constraints. Despite the nonlinear nature of the problem, it is sought to find a robust technique for a wide range of typical low-thrust transfers with reduced computational intensity. Another important aspect of our developed methodology is the representation of low-thrust trajectories by Fourier series with which the number of design variables reduces significantly. Emphasis is given on simplifying the equations of motion to the possible extent and avoid approximating the controls. These facts contribute to speeding up the solution finding procedure. Several example applications of two and three-dimensional two-body low-thrust transfers are considered. In addition, in the multi-body dynamic, and in particular the restricted-three-body dynamic, several Earth-to-Moon low-thrust transfers are investigated.

A MARKET-BASED APPROACH TO 3D PRINTING FOR ECONOMIC DEVELOPMENT IN GHANA

The purpose of this report is to create the foundation for further study of a market-based approach to 3D printing as an instrument for economic development in Ghana. The delivery of improved products and services to the most underserved markets is needed to spur economic activity and improve standards of living. The relationship between economic development and the advancement of technology is considered within the context of Ghana. An opportunity for market entry exists within both the bottom of the economic pyramid and the mid-segment market. 3D printing (additive manufacturing) has proven to be a disruptive technology that has demonstrated an ability to expedite the speed of innovations and create products that were previously not possible. An investigation of how 3D printers can be used to create improved products for the most underserved markets within Ghana is presented. Questions are asked to elucidate how and when adoption of 3D printers and 3D printed products may occur in the future. Based upon the existing barriers to adoption, 3D printing technology must improve before widespread adoption will occur in Ghana.