Analysis of Light Sail Geometries and Stability for Directed Energy Interstellar Propulsion Author: Jacob Erlikhman, N/A, Researcher/Student, University of California, Santa Barbara Abstract Background: A 1 m2-class light sail has been proposed as a method of achieving speeds of appreciable fractions of the speed of light using a ground-based, kilometer-scale, GW to multi-GW phased laser array. Such a sail could accelerate a light (~10 g) spacecraft to 0.2 c over several minutes of continuous acceleration, enabling travel at the relativistic speeds necessary for interstellar missions. Abstract Objectives: Due to the enormous loads incident on the sail, rapid acceleration, and the inherent mass constraints of the spacecraft, the sail must be designed to passively remain trapped in the laser beam, which may be Gaussian or shaped with a central null. Abstract Methods: We have conducted fully analytic, as well as numerical simulation analyses in COMSOL, over different sail geometries, spacecraft mass distributions, and beam shapes. Abstract Results: A number of stable designs have been found in the regimes of a central-null beam and Gaussian beams profile; a parabolic and conic sail; and orientations of the sail towards and away from the direction of travel. TRL Assessment: Currently TRL 1, progress towards TRL 2. Abstract Development: Future simulations will include structural and environmental effects, including sail tearing, deformations, vaporization due to absorption, and impacts of interplanetary medium (IPM) particles, advancing the technology towards a TRL 3 prototype. Abstract Near-Term Technical Milestones: Sail system requirements will be derived from the analysis, including maximum absorption, minimum reflectivity, material strength and rigidity. This data will be used to drive sail structural design and identify materials for the construction of a prototype. Abstract Conclusions: Passive-spacecraft stability in the acceleration phase of directed energy interstellar propulsion is possible with the co-design of the space and ground segments. Sail geometry and spacecraft center of gravity are primary stability parameters.