Telescope Enclosures

Abstract

The large cm-wavelength telescopes at Jodrell Bank, Effelsberg, Parkes, Green Bank and others are open-air telescopes. The smaller telescopes, and in particular those for short wavelengths, are either closed or placed in an enclosure. A closed telescope is one in which the BUS is covered by the front panels and the rear cladding to prevent direct interaction with the thermal environment, and in some cases to allow ventilation. Several telescopes are placed in an astrodome with a slit that can be opened for observation, or which is more or less permanently covered by a radio transparent membrane. The sides and the rear of an astrodome are usually metal plate walls. The astrodome follows the motion of the telescope. This limits the size to manageable structures, at reasonable costs. The over-hemispherical radome, on the other hand, has a radiowave transparent skin, is fully closed, and is stationary. The telescope inside the radome can move and observe in all directions through the radome, with blockage by the supporting space frame. The astrodome and radome are part of the telescope’s concept of thermal and wind protection. The earlier mmwavelength telescopes were built from aluminium to reduce mass and placed in a ventilated radome to cope with the larger thermal expansion of aluminium. The HHT, CSO, and JCMT telescopes with astrodome protection are listed in Table 3.1 and are shown in Figs. 3.1–3.3, and the radome of the Onsala 20–m telescope is shown in Fig. 3.4.