The Discovery Channel Telescope (DCT) is a project of Lowell Observatory in conjuction with the Discovery Channel to design and construct a 4.2-meter clear aperture telescope and support facility on a site approximately 40 miles southeast of Flagstaff, Arizona, USA. The site is an undisturbed mountain top at an altitude of 7800-feet. Design and construction of the telescope enclosure includes all of the site utilities, access road to the site along with the fixed base enclosure, telescope pier and rotating dome structure.
The details covered in this paper are the decisions and rationale of the DCT enclosure conceptual design completed by M3 Engineering & Technology Corporation (M3).
Aspects of the design and experience of the Hobby-Eberly Telescope (HET) were incorporated in the SALT facility design. The characteristics of the local environment were taken into account to ensure a building that is cost effective and functional. The effect of heat from the control room and other warm areas were studied and their locations changed to limit thermal effects. A steel false floor, incorporating forced ventilation and extending around the telescope azimuth pier, was installed. This prevents heat radiating from large concrete surfaces with temperatures potentially higher than ambient. Because site testing (i.e. micro thermal measurements) indicated high turbulence within ~5 m of the ground level, the telescope and pier were raised to improve dome seeing. The SALT site is significantly windy all year round (median velocity = 4.8 m/s), and this was utilized to design better ventilation of the facility using adjustable louvers for natural ventilation. Results of a computational fluid dynamic analysis (CFD) are presented which show an adequate temperature distribution at wind speeds as low as 0.5 m/s. The telescope chamber and dome are build out of insulation panels to ensure low thermal losses during the day when the chamber is air conditioned and thus limit electricity consumption and thermal gradients. Large equipment that emit heat or vibration are housed in a separate utility building 50 m from the telescope in the non-prevailing wind direction in order to limit their effect on the telescope. Vented air from the building is also released at this site.