Creating optimal observing schedules for a starshade planet-finding mission

Missions designed to use a starshade (also known as an external occulter) in conjunction with a space telescope to find and characterize planets around nearby stars provide the capability to directly image terrestrial planets in the habitable zones of nearby stars.12 However, this architecture also creates some challenges in scheduling science observations. The starshade is a separate spacecraft from the telescope and they operate tens of thousands of kilometers apart. The two spacecraft must be realigned with each new target star in order for the starshade to block the starlight from entering the telescope. This means that large amounts of time and propellant are needed to slew the observatory from one target to the next. Therefore it is imperative that observations be scheduled efficiently to minimize time and propellant use while maximizing science return. In this paper we report on a method of optimizing the observation path for a starshade mission by weighing factors such as science return, architectural constraints, and mission costs. Because the mission constraints and costs are time variable and because the number of potential star paths is so large (>;1>;<;10²⁰⁰), typical optimization schemes (e.g., Traveling Salesman, Genetic Algorithms) are not applicable. Instead we conduct a smart-random search by weighting each star-to-star step by several factors that increase the likelihood of choosing a higher return / lower cost step. We then generate thousands of Monte Carlo paths and use this ensemble to evaluate the capabilities and constraints of this mission design. We find that a starshade mission can fulfill all the requirements of the Terrestrial Planet Finder program including searching at least 30 Habitable Zones (HZ), spectrally characterizing any discovered planets, and revisiting some planetary systems to establish orbital information. This can be done using less than 1/3 of the total telescope time, leaving the rest of the missi on time for other, general astrophysics observations with the highly capable space telescope. We also look at the robustness of the mission to different science assumptions such as the fraction of all stars that contain terrestrial planets and the level of dust around the target stars (exozodi). We find that this is a robust and capable mission design and that our method can find efficient paths for conducting the mission.