Understanding HWO's Field of Regard and Characterization Requirement Trade Space with a Dynamic Observation Scheduling Algorithm

Original Abstract

The Habitable Worlds Observatory (HWO) aims to image and characterize at least 25 ExoEarth candidates (EECs). Achieving this goal requires a detailed understanding of the observatory's design trade space, including the operational efficiency of the EEC survey. This study quantifies the impact of two critical parameters: the instantaneous field of regard (FoR) and the number of characterization observations required per EEC ($N_\text{char}$). We introduce a novel dynamic scheduling algorithm implemented within the EXOSIMS framework that models information gain during the mission. The scheduler models the orbital information known about each planet and forecasts detection probabilities to make scheduling decisions. We explore a multi-dimensional trade space, varying aperture size (6.5 m and 8.0 m), dedicated EEC survey time (2.5, 5.0, 7.5 years), $N_\text{char}$ (1 to 4), and FoR ($15^\circ$ to $135^\circ$). Our results demonstrate that the FoR is a major driver of the mission yield, with the yield decreasing significantly when the FoR is less than $90^\circ$. We find that increasing $N_\text{char}$ imposes a significant cost to mission yield, as each additional characterization required reduces yield by approximately 22%. The cumulative impact of requiring four characterizations instead of one lowers the yield by approximately 52%. This harsh penalty can be partially mitigated by increasing the survey duration. The relative yield loss when increasing $N_\text{char}$ from 1 to 2 is 38% for a 2.5 year survey and 14% for a 7.5 year survey. Our results highlight the complex interactions between HWO's engineering constraints and science requirements, and emphasize that the EEC survey efficiency is a critical component of HWO's design space.