The Telescope: Structure
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 structure consists of two major components: the azimuth and elevation structures. The elevation structure provides a mounting for the telescope optics and the laser guide star facility (LGSF). The azimuth structure supports the elevation structure and two large Nasmyth platforms where the observatory instruments and adaptive optics systems are located.
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.