Research On Control Technology Of Precision Image Stabilization System In Space Telescope

With the development of astronomy, science and technology, it is necessary todevelop a high-resolution, large field of view, wide spectral band telescope. Becauseof the effects of atmospheric disturbances, dispersion effect, strong absorption ofultraviolet by ozone and atmospheric background noise, the observations ofGround-based telescopes subject to certain restrictions. Space astronomicalobservations can completely get rid of the atmosphere, receive a wide wavelengthrange and closely reach the diffraction limit of the telescope. All these favorableconditions make research on space telescopes become a hot topic in the field ofastronomical observations. However, as the spacecraft is the platform of spacetelescope, the attitude change of the spacecraft, orbital precession, slight vibration ofmoving parts, even the movement of astronauts can have an impact on spaceexploration. In the worst-case the space telescope cannot track and capture the target.Even it is possible to track and capture the target, within the exposure time of imagingsensor, the moving between spot and sensor coursed by random vibration of thespacecraft will result in blurred images. Seriously it can affect the detection accuracyof Space Telescope. In order to achieve the desired detection accuracy, measures mustbe taken to suppress the jitter of the platform to achieve high image quality.Vibration isolation systems and fine tracking systems with capability of gooddisturbance rejection capability are generally used to suppress the vibration incurrently space platforms. There are two aspects in the study of image stabilization.The first is the systematic study of feedback compensation method; the second is thestudy of motion detection.In this paper, research on precision image stabilization system of the domesticspace telescope are made first, then, the analysis of the sources which affect the boresight stability of space telescope are performed. According to the scope and intensityof the ISS vibration spectrum measured by ESA, the space telescope imagestabilization system is divided into: passive vibration isolation system, coarse imagestabilization system and precision stabilization system, then the bandwidth range ofeach system are divided. At last, we focus on the research on the precision controltechnology of two-dimensional image stabilization system, propose technicalsolutions and segment system metrics. Around large-aperture fast steering mirror optical compensation system and fineguidance sensor, which is the two major components of the two-dimensional precisionimage stabilization system, technical problems are tackled. The improved sub-pixelcentroid algorithm, which is used in fine guidance sensor, is raised. The electronicshardware and software of large-aperture fast steering mirror optical compensationsystem, which consist of DSP digital controller, PZT drive board andmicro-displacement detection circuit, are designed. System identification of large-aperture fast steering mirror is completed and high-precision control algorithm forlarge-caliber fast steering mirror is designed.This paper has three major innovations:On the basis of the study of image stabilization technology in abroad spacetelescope and the spectrum and intensity of the disturbance source in space platforms,the space telescope image stabilization scheme consisting of―vibration isolationsystem, pointing and tracking system and fine image stabilization system‖is proposed.Fine image stabilization control system, which is one of the core technologies ofspace telescope, is studied in detail. A solid foundation is laid for the realization ofengineering application of our large-aperture, large field of view and high imagequality space telescope in the future.A system identification of large-aperture (340mm×330mm) fast steering mirror isproposed based on the overall design of fine image stabilization system. A stableintestine and optical control loop, which makes the bandwidth of the optical closeloop superior than8Hz, is designed based on the analysis of the first order frequencyand mathematical model of fast steering mirror mechanism.Aim at fine guidance detection of fine image stabilization control system, varioussub-pixel centroid algorithms are studied. A sub-pixel centroid algorithm combiningprecision and efficency is designed. Experiments show that the algorithm can achievesub-pixel accuracuy of1/50pixels under the condition of SNR of20and frame rate of110fps. The technical challenge of high precision and high frame rate requirement isovercomed.Aim at the compensation link of the fine image stabilization control system, asimulating verification system is designed, and the hardware and softwareenvironment, integrating DSP digital controler, PZT driver and micro-displacementdetection technology, is build. The performance of the built system, with ripple noiselower than0.12mV under5KHz and voltage resolution of0.5mV, is better thansimilar products with one order of magnitude. Favorable conditions for the realization of fine driver control system with large-aperture fast steering mirror are produced.