Large Space Optics Using System Identification

Temperature control of space optics is a relatively new field. The main components of a temperature control loop are spatially distributed temperature heaters, controllers, and spatially distributed temperature sensors (thermistors or thermocouples). Traditional Proportional Integral Derivative (PID) control approaches do not achieve optimal system performance when there are significant delays between the control inputs or disturbances and observed state variables, and when the system is of higher order. PID controllers often cannot achieve optimal energy consumption, as well as high control performance and accuracy. Besides these challenges, optimal tuning of PID controllers for systems with many inputs and outputs (such as the thermal control system for space telescopes) is a highly nontrivial and still active research problem. Recently, model-based control approaches developed using a lumped model of temperature dynamics were developed. These lumped model representations may be too simplistic to produce accurate results and do not include the coupling between the absorbed external flux and the system dynamics. System identification (SID) uses statistical methods to build mathematical models of dynamical systems from measured data. It is the basis for modern data-driven control systems, in which concepts of system identification are integrated into the controller design laying the foundations for formal controller optimality proofs. Our proposed innovation is an active thermal control using system identification (ATC-SID) method to enable a: Large mirror (>4-meter diameter – monolithic or segmented) with diffraction limited performance at wavelengths less than 500 nm (< 40 nm RMS wavefront error, WFE). Total cost of the primary mirror below $100M. Our ATC-SID innovation will enable thermal control (< 1 mK) to reduce wavefront stability to < 10 pm RMS per 10 min).

The key NASA applications are space flight missions with large telescopes, particularly operating in the ultraviolet or shorter wavelength-region. These include the Large UV/Optical (LUVOIR) and Habitable Exoplanet (HabEx) Missions. A potential exoplanet mission requires total telescope wavefront stability on order of 10 pico-meters RMS per 10 minutes. Our active thermal control using system identification (ATC-SID) is clearly an enabling technology for upcoming NASA large space telescope missions.

According to the "Photolithography Market 2019 Global Industry Analysis to 2025" research report published by Market Research Future, the global photolithography market is projected to grow at 4.26% annual rate and reach USD 7.34 billion during 2019 to 2025. Our ATC-SID method is a significant enabling technology for large ultra-violet optics for photolithography.

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