<title>Gemini primary mirror support system</title>

Active optics in modern large optical telescopes

“…For these, the development of active optics control systems, which can operate in closed loop at time intervals of the order of one minute, will be essential. Telescopes with somewhat different applications of active optics include the Chinese LAMOST project (Su, Cui, Wang and Yao [1998]) and the hexapod telescope of the University of Bochum (see the overview given by Wilson [1999]). LAMOST is a 4 m meridian type Schmidt telescope with a thin reflecting aspheric corrector plate, where the optimum shape of this plate depends on the zenith distance.…”

“…The generated high spatial frequency aberrations, the so-called print-through, depend clearly on the specific weight and the elasticity module of the mirror material, on the thickness of M1 and the density of supports. But it can also be influenced by the general type of the support system, for example if part of the weight of the mirror is supported by a continuous pressure field at the back surface as realised in the support of the primary mirrors of the Gemini telescopes (Stepp and Huang [1994]). The stiffness of M1, a central parameter for the active optics design, is a function of the diameter of M1, its thickness and its elasticity module.…”

<title>Thermal analysis on hex-placement patterns of the Gemini primary mirrors</title>

“…This holds only true in view of the residual surface errors after performing active optics corrections with the active optics system ofGEM1NI [5].…”

“…Aberrations of piston, tilts, and focus were removed from each of the raw optical surface, and then active optics corrections were performed. Listed in Table 1 were the selected results due to the thermal strains using equation (5) for the average temperature distributions. Table 1 is for a sine distribution with m1 and Mode 2 is for m=2.…”

“…This implementation gives much more flexibility to investigate the thermal effect in this parametric study because the nodal temperatures can be dealt by generic nodal loading terms. The following expression which is a combination of two trigonometric functions was employed for an average temperature loading distribution across the radius ofthe primary mirror: Ta(r)=Asn+Bcos (5) ,where Ta(r) is the temperature distribution based on CX and is a function ofa radial location ofr. A and B are constants, R0 is the radius ofthe primary mirror, and n and m are integers which vary from 0 to 4.…”