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The Strategic Astrophysics Technology (SAT) program has recently identified several critical technology gaps related to future missions that have direct relevance to thermal control methods for optical payloads: (1) thermally stable telescopes, (2) sensing and control at the nanometer level or better, and (3) sensing and control at the picometer level [1]. Implementing very tight control stability on optical payloads in the space environment to achieve precise line of sight and wavefront control is more than just a thermal problem. It is a combination of system design challenges implementing thermal, electronics, and control methods. These challenges are further complicated by size, weight, and power (SWAP) constraints for large-scale optical platforms due to both quantity of sensors and physical separation between sensing and control electronics. For thermal hardware, control errors arise from sensors indirectly coupled to the controlling heat source that may result from installation constraints, sensor or heater attachment methods, or poor thermal diffusivity. For electronics, control errors arise due to system resolution limitations which are dependent on bit accuracy over the temperature range of interest, current and voltage source accuracy, sensor self-heating, noise sources, sampling rates, and circuit averaging methods. Errors arise from limitations in the control methods such as over- and under-shoot with bang-bang (on/off) or proportional-integral-derivative control (PID). Within the PID control method, there are many nuances to the implementation as well, such as the need to tune each control zone for optimal control. This paper presents a description of the challenges and opportunities that come with high precision space telescope thermal control for candidate future astrophysics missions like LUVOIR or HABEX and provides examples of thermal design and analysis methodologies underway for the WFIRST program.
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