The telescope structure is designed as an altitude over azimuth (alt-az) mount. This allows the telescope to be very compact (relatively speaking) and provides direct load paths from the telescope down through the structure to the pier and foundations.
The Nasmyth platforms are located 7 meters (23 feet) below the elevation axis, to accommodate the largest instruments that will be mounted on TMT. The telescope elevation axis is located above the primary mirror. This enables the articulated tertiary mirror to direct the science light to the instruments, and the structure has been designed to provide the necessary clearance for the light path from M3 to the Nasmyth instrument stations, as shown in the following figure.
The drive motors used to move the telescope in azimuth and elevation will be direct drive “linear” motors, curved to match the large radii of the drive arcs. Position feedback will be provided by linear tape encoders.
Because TMT is a large structure, elevators, stairs and walkways will be included to provide access to all subsystems on the telescope. All the utility lines (power, cooling water, compressed, air, refrigerants, data, etc.) required by the telescope subsystems will be built into the telescope structure. The entire telescope is composed of many subsystems. The Telescope Structure Subsystem design is preparing for the final design review and design work is progressing on the Refrigeration System, the Cryogenic Cooling System and the Telescope Control System. Of note is the impressive design for the Segment Handling System that has received industry awards. A video describing the Segment Handling System shows the prototype segment handling robot in action.