Development of space-based diffractive telescopes

Membrane diffractive optical elements formed by fabricating microstructures on the substrates have two important characteristics,ultra-light mass(surface mass density<0.1 kg/m2)and loose surface shape tolerances(surface accuracy requirements are on the order of magnitude of centimeter).Large-aperture telescopes using a membrane diffractive optical element as the primary lens have super large aperture,light weight,and low cost at launch.In this paper,the research and development on space-based diffractive telescopes are classified and summarized.First,the imaging theory and the configuration of diffractive-optics telescopes are discussed.Then,the developments in diffractive telescopes are introduced.Finally,the development prospects for this technology used as a high-resolution space reconnaissance system in the future are summarized,and the critical and relevant work that China should carry out is put forward.

Active vibration control of a large space telescope truss based on unilateral saturated cable actuators

Due to obvious advantages,such as light weight,easy folding and deployment and high accuracy of optical imaging,the membrane diffraction large space telescope has currently been one of the hot research topics.Because of the influence of external disturbance and attitude adjustment,the large space telescope will occur a certain degree of vibration inevitably,affecting the imaging accuracy of the space telescope for Earth.Thus,to satisfy the requirement of imaging accuracy,it is necessary for the space telescope to adopt appropriate vibration control methods.In this paper,the active vibration control of the large space telescope is studied using cables as active actuators.Considering that cables can work under tension but not under pression and the tensile capacity is limited,the unilateral and saturated characteristics of cable actuators are taken into account during control design in this paper.Firstly,the dynamic model of the membrane diffraction space telescope is established using the finite element method(FEM).Secondly,in combination with the linear quadratic regulator(LQR)and the bang-bang regulator,a piecewise cost function is used to design the active vibration control law.Next,the controllability criterion and the genetic algorithm(GA)are adopted to determine the optimal positions of cable actuators.Finally,the validity of the proposed control method is verified by numerical simulations.Simulation results indicate that the vibration of the space telescope can be suppressed effectively using the proposed control method,and the imaging requirements of the telescope may be realized using the least cable actuators,whose minimum quantity and position distribution are determined in this paper.