UltraSail is a next- generation ultra-large (km² class) sail system. Analysis of the launch, deployment, stabilization, and control of these sails shows that high-payload-mass fractions for interplanetary and deep-space missions are possible. UltraSail combines propulsion and control systems developed for formation- flying microsatellites with a solar sail architecture to achieve controllable sail areas approaching 1 km². Electrically conductive CP-1 polyimide film results in sail subsystem area densities as low as 5 g/m². UltraSail produces thrust levels many times those of ion thrusters used for comparable deepspace missions.