Two-Stage Attitude Control for Direct Imaging of Exoplanets with a CubeSat Telescope

摘要

This work outlines the design and development of a prototype CubeSat space telescope to directly image exoplanets and/or exozodiacal dust. This prototype represents the optical payload of the miniaturized distributed occulter/telescope (mDOT), a starshade technology demonstration mission combining a 2 meter scale microsatel-lit.e occulter and a 6U CubeSat telescope. Science requirements for the mDOT experiment are presented and translated into engineering requirements for the attitude determination and control subsystem (ADCS). The ADCS will utilize a triad of reaction wheels for coarse pointing and a tip tilt mirror for fine image stabilization down to the sub-arcsecond level. A two-stage attitude control architecture is presented to achieve precise pointing necessary for stable acquisition of diffraction limited imagery. A multiplicative extended Kalman filter is utilized to estimate the inertial attitude of the vehicle and provide input into the aforementioned controller. A hardware-in-the-loop optical stimulator is used to stimulate the payload with scenes highly representative of the space environment from a radiometric and geometric stand point. Scenes rendered to the optical stimulator are synthesized in closed-loop based off a high-fidelity numerical simulation of the underlying disturbances, orbital and attitude dynamics. Performance of the two-stage attitude control loop is quantified and demonstrates the ability to achieve sub-arcsecond pointing using a telescope payload prototype.