SOLAR SAIL TRAJECTORY OPTIMIZATION USING COLLOCATION AND NSGA II

Open Access
Author:
Davis, Elizabeth
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 30, 2008
Committee Members:
  • Robert Graham Melton, Thesis Advisor
Keywords:
  • solar sail
  • collocation
  • evolutionary algorithm
  • trajectory optimization
  • NAGA II
Abstract:
Solar sail spacecraft rely solely on solar radiation pressure for propulsion. Since the acceleration received by radiation pressure increases as the spacecraft nears the Sun, missions to inner solar system planets are commonly proposed. Finding optimal trajectories for such missions can be difficult because the equations of motion must be solved numerically and the optimization problem includes many nonlinear constraints. One technique that has good shown good results is direct collocation with non-linear programming (DCLNP). The method sets up the problem as a non-linear programming problem which is traditionally solved with a method that requires gradient information. However, such solvers generally need a good initial guess to converge. This research found that the trajectory optimization problem formulated as a DCLNP and optimized with the evolutionary algorithm, NSGA II, can be used to create sub-optimal trajectories for the solar sail spacecraft. Although DCNLP includes a number of nonlinear algebraic constraints, these cannot be satisfied exactly with an evolutionary algorithm. Therefore, Pareto multi-objective optimization was used to minimize error in these constraints, while also minimizing the time-of-flight. The resulting trajectories could then be used as initial guesses for more traditional NLP solvers.