<title>Imaging planets about other stars with UMBRAS II</title>

Large space-based telescopes have specic design requirements which oer,challenges to the instrument designer. The optical design and detector fabrication are frozen years before the launch date. The Umbral Mission Blocking Radiating Astronomical Sources (UMBRAS) space mission design consists of a Solar-Powered Ion-Driven Eclipsing Rover (SPIDER) and possibly one or two metrology platforms. The ultimate goal of UMBRAS is to provide pseudo- coronagraphic capability for direct imaging of extrasolar Jovians and other brighter, distant substellar companions. In this paper we discuss operational considerations for the free-ying occulter. Operations consist of maneuvering the SPIDER between targets, alignment with the space-based telescope line of sight to the target, and stationkeeping. Target-to-target maneuvers need to be optimized to conserve propellant. A reasonable balance needs to be determined between target observation rate and the number of targets that are observable during mission lifetime. Velocity matching of the SPIDER with the telescope is essential to mission performance. An appropriate combination of solar electric and cold-gas thrusters provides the ability to match velocities using positional information derived from communication and ranging between telescope, occulter and any metrology stations. Desirable features of using an external coronagraphic vehicle include the ability to obtain coronagraphic data