TMT programmatic requirements have been studied to specify the needed conventional facilities and construction sequence at the summit and at a nearby support location. Minimum excavation of the summit to support the required facility footprint and construction allowances has been defined.
The summit facility supports telescope operations, control room functions, staff summit support, mirror handling, stripping, cleaning, storage and recoating, basic engineering and technical activities and other elements of operation that must be carried out close to the telescope.
Support facilities, near the summit, include a construction camp, dormitories and dining facilities for operations staff, and workshops for maintenance and technical activities.
The TMT enclosure has several key functions. By day, it must protect observatory systems, facilitate a broad range of maintenance activities, and keep the telescope temperature near the expected night time temperature. By night, it must shield the telescope from wind buffeting while allowing enough airflow to keep the interior iso-thermal to limit seeing degradation due to air turbulence in the enclosure.
TMT has selected an innovative, structurally efficient calotte enclosure design that, by its spherical shape and circular “shutter” aperture, fulfills key functional requirements with lower mass (and hence lower cost) than possible for previous enclosure designs.
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, etc.) required by the telescope subsystems will be built into the telescope structure.