Abstract. Significant scientific and technical advances of recent times in the study of remote regions of the Universe, obtaining images of space and ground-based objects with high resolution became possible thanks to the use of new technologies for the development of large-size optical telescopes. A rise in the main telescope mirror diameter leads to an increase in mass and enhances the possibility of deforming the mirror surface and the telescope’s structural elements. This problem can be overcome by using segmented or flexible mirrors, the shape of which is maintained with the use of active optics. However, atmospheric turbulence degrades the quality of images of space objects obtained by ground-based telescopes. To compensate for the influence of the atmosphere, adaptive optics methods are used in most optical telescopes. An overview of the current state of optical telescopes development is presented. Consideration is given to large ground-based optical telescopes with composite and flexible mirrors with aperture diameter exceeding six meters, controlled by adaptive systems. The high resolving and penetrating capabilities achieved during the creation and modernization of large-sized ground-based optical telescopes allow to set and solve new and important scientific and applied problems in the study of space  objects of natural and artificial origin. One of these tasks, which has become particularly relevant in recent years, is the detection of small-sized fragments of space debris near spacecraft and orbital space stations. 

Keywords: optical telescopes, aperture diameter, flexible mirrors, segmented mirrors, active optics, adaptive optical systems

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