Design of the Discovery Channel Telescope mount

The Discovery Channel Telescope is a 4.2-meter clear aperture telescope undertaken by the Lowell Observatory in Flagstaff, Arizona. It will feature an interchangeable secondary assembly to allow the use of either a prime focus instrument or a secondary mirror. In addition, it will have an active optical system and provisions for a wide range of instruments. This paper describes the design of the telescope mount and drive systems. Particular challenges associated with the design include: consideration for the weight of the 3500 lb Prime Focus Assembly (PFA) instrument; interchangeable secondary assemblies; and providing thermal and mechanical stability in between updates to maintain alignment between optical elements.