Study On Control Methods Of Honeycomb Mirror Temperature And Mirror Seeing

Temperature is one of the key factors which affect the high resolution image quality oflarge aperture astronomical telescope. When ambient temperature varies quickly, heattransfer appears between primary mirror blank and the ambient air because oftemperature difference. Primary mirror seeing result from the air turbulence of heatconvection, may derange the atmosphere along the optical path, and lead to opticalaberrations and awful image quality. Minimum primary mirror seeing phenomenon’seffect on the high resolution image quality of large aperture astronomical telescope isthe main purpose of the dissertation.According to physical principle of primary mirror seeing, there are two commonmethods to control primary mirror seeing. One method is control the temperature ofprimary mirror, making the temperature difference between the reflecting surface ofprimary mirror and ambient air in a small range; another is using “air knife” alongreflecting surface of primary mirror to minimize the turbulence of primary mirrorseeing.In this paper, primary mirror seeing and its improvement effect of classical mirror andhoneycomb mirror are studied by thermal field calculation and empirical equationabout primary mirror seeing. Primary mirror seeing quantitative calculation and “airknife” effect of classical mirror are analyzed through temperature field analyticalsolution in detail. A flexible and easy operational thermal control method is presented.A single honeycomb cell model hypothesis is introduced for large aperturehoneycomb mirror thermal control system research. Taking the4m honeycomb mirrorfor example, computational fluid dynamics and finite element method are used tocalculate the honeycomb mirror temperature field and thermal deformation.4mhoneycomb mirror thermal control effect is analyzed in primary mirror seeing andthermal deformation two aspects. Some specific engineering problems in4mhoneycomb mirror thermal control system are discussed.“Air knife” flow model isintroduced to calculate the “air knife” flow field characteristics and the opticalaberrations result from air flow. Through this research, a whole set of technical method which is used to controlprimary mirror seeing and temperature has been worked out. These methods used inthis paper lay a strong foundation for the future development of larger aperture highresolution image telescope in the primary mirror temperature control aspect.