Adapting the 23m LST-North mechanical structure design for the strong Chile seismic environment

Abstract

The 23-meter-diameter Large-Sized Telescope (LST) is the largest size telescope of the next generation Cherenkov Telescope Array (CTA). The first telescope, LST-1, was installed at the Roque de los Muchachos Observatory (ORM) on La Palma at an altitude of 2,250 m in 2018 and has been in operation since 2019. Its ultra-lightweight structure (110 tons) enables extremely rapid repositioning (180° in 18 seconds) and has been designed to withstand extreme environmental conditions, including storms and winds exceeding speed up to 200 km/h. To deploy the same solid telescope design at the CTA Southern Observatory in Chile, the structure must be adapted to the significantly higher seismic demands of the site. To address this challenge, the Max Planck Institute for Physics (MPP) has proposed the integration of a seismic isolation system with the proven LST-1 structural design. This approach substantially reduces seismic loads and dynamic amplification, thereby avoiding extensive structural modifications and enabling the existing telescope design to be transferred to the Chilean site with only minor adaptations. In this contribution, we present the proposed seismic isolation concept and its feasibility studies. MPP is responsible for the mechanical structure of the LST and has validated the concept through detailed finite-element analyses and long-term structural lifetime assessments.