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.
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. Control is carried out by the Telescope Control System (TCS). The TCS controls and/or coordinates the telescope structure, optics, science instruments and the adaptive optics systems.
Because TMT is a large structure, an elevator, an aerial service platform, stairs and walkways will be included to provide access to all subsystems mounted on the telescope. The infrastructure to route and support the utility lines (power, cooling water, compressed air, refrigerants, cryogen, data, etc.) required by the telescope mounted subsystems, the Telescope Utility Services, will be built into the telescope structure. The Telescope Utility Services Final Design was completed in October, 2020. The entire telescope is composed of many subsystems. The Telescope Structure Subsystem completed its final design closeout review in November, 2019 and the first of six production readiness reviews in April, 2021. 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. Design work is progressing on the Refrigeration System, the Cryogenic Cooling System and the Telescope Control System.
Rendering of the front view of the telescope structure showing the NFIRAOS instrument on the left and the WFOS instrument on the right. For perspective, the telescope is ~55 meters or 180 feet wide and ~50 meters or 160 feet tall. The segment handling platform is to the rear and the mirror cleaning arms can be seen at the front and rear edges of the primary mirror. Image credit to Mitsubishi Electric Corporation and National Astronomical Observatory of Japan
Segment Handling Robot that traverses beneath a mobile bridge to remove and replace mirror segments. Image credit to Mitsubishi Electric Corporation
