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Basic specifications of 30m telescope concept under consideration by the Ground Telescope Group are listed in Table 1. These specifications have been reviewed by the Science Group, and were designed so as to be technologically practical, providing a telescope with functionality required to carry out scientific observations. These specifications are subject to change as necessary based on further review to coordinate with international requirements.

Items presently under investigation and the groups responsible are listed in Table 2.

Table 1: Basic specifications of JELT concept

M1 F/1.5, 30 m primary mirror
(segmented type)
Segmented mirror material CFRP/ zero-expansion glass/ zero-expansion pore-free ceramic
Optical system 3 Aspherical mirror system
Focus Nasmyth foci × 2 or 4
Field of view Radius: 10 arcmin
Wavelength band Visible through medium infrared
Auxiliary observational equipment Optical spectrograph, infrared spectrograph, imaging camera
Dome Radius: 50 m

Table 2: R/D projects related to JELT

Development item Group conducting investigation
Carbon fiber-reinforced plastic (CFRP) mirror Mitsubishi Electric
Zero-expansion pore-free ceramic mirror Taiheiyo Cement Company and National Astronomical Observatory
Extremely high precision grinder Nagase Integrex
Adaptive optic system with laser guide star National Astronomical Observatory
Lightweight truss structure Nagoya University
Segment support adjustment mechanism Kyoto University and Mitsubishi Electric
Optical design Dr. Nariai and Dr. Iye
Direct-drive motor Mitsubishi Electric

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