Not coincidentally, most of the world’s best astronomical sites are in seismically active areas. As telescopes increase in aperture, they become increasingly sensitive to seismic loads. In this workshop, we want to collect the knowledge, experience, and lessons learned from the previous generations of observatories, to inform the design and construction of future observatories, including the ELTs (ELT, GMT, and TMT). Topics for the workshop include earthquake-induced damage to observatories (telescopes, instruments, enclosures), seismic protection systems and improvements in existing observatories, design of seismic protection systems for new and future observatories, processes and operational procedures for recovery and return to operations following seismic events, and lessons learned that can be applied to the design and operation of future observatories.
National Astronomical Observatory of Japan (NAOJ) has had the responsibility for the Telescope Structure System (STR) of Thirty Meter Telescope (TMT) and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary/final design and pre-production work since 2012. TMT defines that STR shall be designed to withstand earthquakes up to the levels of the 1000-years annual return period as keeping accelerations at the mirror/instrumental interface points below the specified thresholds. In this paper, we present the Seismic Isolation System (SIS) of TMT STR, as focusing on (1) the design to achieve compatibility of two conflicting performances that are the rigid connection to the ground during normal observations and flexible movement during seismic to suppress the seismic energy, (2) prototype results of the seismic isolation system, and (3) compliance status of the seismic requirements which is evaluated by time history analysis using the Finite Element Method (FEM) model of TMT STR.
The thermal behavior of the Thirty Meter Telescope (TMT) Telescope Structure (STR) and the STR mounted subsystems
depends on the heat load of the System, the thermal properties of component materials and the environment as
well as their interactions through convection, conduction and radiation.
In this paper the thermal environment is described and the latest three-dimensional Computational Solid Dynamics
(CSD) model is presented. The model tracks the diurnal temperature variation of the STR and the corresponding
deformations. The resulting displacements are fed into the TMT Merit Function Routine (MFR), which converts them
into translations and rotations of the optical surfaces. They, in turn, are multiplied by the TMT optical sensitivity matrix
that delivers the corresponding pointing error. Thus the thermal performance of the structure can be assessed for
requirement compliance, thermal drift correction strategies and look-up tables can be developed and design guidance can
be provided.
Results for a representative diurnal cycle based on measured temperature data from the TMT site on Mauna Kea and
CFD simulations are presented and conclusions are drawn.
KEYWORDS: Telescopes, Optical instrument design, Computer aided design, Mirrors, Electroluminescence, Control systems design, Control systems, Earthquakes, Safety, Thirty Meter Telescope
We present an overview of the preliminary design of the Telescope Structure System (STR) of Thirty Meter Telescope (TMT). NAOJ was given responsibility for the TMT STR in early 2012 and engaged Mitsubishi Electric Corporation (MELCO) to take over the preliminary design work. MELCO performed a comprehensive preliminary design study in 2012 and 2013 and the design successfully passed its Preliminary Design Review (PDR) in November 2013 and April 2014. Design optimizations were pursued to better meet the design requirements and improvements were made in the designs of many of the telescope subsystems as follows: 1. 6-legged Top End configuration to support secondary mirror (M2) in order to reduce deformation of the Top End and to keep the same 4% blockage of the full aperture as the previous STR design. 2. “Double Lower Tube” of the elevation (EL) structure to reduce the required stroke of the primary mirror (M1) actuators to compensate the primary mirror cell (M1 Cell) deformation caused during the EL angle change in accordance with the requirements. 3. M1 Segment Handling System (SHS) to be able to make removing and installing 10 Mirror Segment Assemblies per day safely and with ease over M1 area where access of personnel is extremely difficult. This requires semi-automatic sequence operation and a robotic Segment Lifting Fixture (SLF) designed based on the Compliance Control System, developed for controlling industrial robots, with a mechanism to enable precise control within the six degrees of freedom of position control. 4. CO2 snow cleaning system to clean M1 every few weeks that is similar to the mechanical system that has been used at Subaru Telescope. 5. Seismic isolation and restraint systems with respect to safety; the maximum acceleration allowed for M1, M2, tertiary mirror (M3), LGSF, and science instruments in 1,000 year return period earthquakes are defined in the requirements. The Seismic requirements apply to any EL angle, regardless of the operational status of Hydro Static Bearing (HSB) system and stow lock pins. In order to find a practical solution, design optimization study for seismic risk mitigation was carried out extensively, including the performing of dynamic response analyses of the STR system under the time dependent acceleration profile of seven major earthquakes. The work is now moving to the final design phase from April 2014 for two years.
Conference Committee Involvement (5)
Ground-based and Airborne Telescopes X
16 June 2024 | Yokohama, Japan
Ground-based and Airborne Telescopes IX
17 July 2022 | Montréal, Québec, Canada
Ground-based and Airborne Telescopes VIII
14 December 2020 | Online Only, California, United States
Ground-based and Airborne Telescopes VIII
13 December 2020 | San Diego, California, United States
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