Integrated control scheme for a large membrane diffractive space telescope

Abstract

For higher resolution, next-generation space telescopes would be equipped with 10–20 m scale membrane diffractive primary lenses, and would have 100 m scale focal length. The large and flexible structure makes high-accuracy and high-stability control a great challenge. Specifically, both high-frequency and low-frequency disturbances must be attenuated, and the relative motion between the primary lens and the receiver (composed of the correcting optics and the imaging sensor) must be controlled. This paper presents a novel integrated control scheme to achieve the strict control goals. The dynamic model of a membrane diffractive space telescope is presented, where both high-frequency and low-frequency disturbances are considered. Nonlinear deformation of the flexible structure is also taken into account. The integrated control scheme consists of 3 parts: (1) an Agile Stable Precision platform (ASP), which can not only reduce the high-frequency vibrations for the receiver but also act as the actuator in the receiver control system; (2) a neural network controller for the spacecraft bus, which control the attitude of the spacecraft bus under uncertain low-frequency disturbances; (3) a finite-time neural network controller for the receiver to make the relative position and attitude of the receiver track on the expected state as fast as possible. Numerical simulations were carried out to verify the superiority of the integrated control scheme. Compared with traditional single stage spacecraft control (i.e., without the ASP), the accuracy and stability of the relative position and attitude are improved by at least one order of magnitude, and the settling time is greatly reduced.