ExoplanetSat is a 10 × 10 × 34-cm, 5-kg space telescope designed to detect exoplan-ets around the brightest Sun-like stars via the transit method. Achieving this objective while meeting strict mass, volume, and power constraints necessitates an innovative high-precision pointing and attitude determination and control subsystem (ADCS) design. This paper will present the overall ADCS hardware and software design of ExoplanetSat. The software description will focus on the payload operation during slews (efficient window generation for stars entering the field of view) as well as the guidance, navigation, and control algorithms for high-precision pointing with two-stage actuation. Analyses and results on the achievable pointing precision using a high-fidelity simulation will be presented. To demonstrate this two-stage control idea in hardware, a testbed on a spherical air bearing was designed, fabricated, and tested at the Massachusetts Institute of Technology (MIT) Space Systems Laboratory (SSL) in collaboration with Draper Laboratory. This hardware-in-the-loop testbed successfully demonstrated precision pointing, raising this subsystem to a technology readiness level (TRL) of 5. Furthermore, results from this testbed were used to validate the simulation results, thereby increasing the confidence in results produced by the simulation.
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