Design, manufacturing, and quality control of the mechanical structures of the small size telescopes for CTAO

Abstract

The Cherenkov Telescope Array Observatory (CTAO) will be composed of two arrays of imaging atmospheric Cherenkov telescopes (one in each hemisphere): in the Northern array, located at the Roque de los Muchachos Observatory in the Canary island of La Palma, there will be 4 large-sized telescopes (LSTs) and 9 medium-sized telescopes (MSTs); the Southern array, at the Paranal Observatory in Chile, will include 2 LSTs, 14 MSTs, and 37 small-sized telescopes (SSTs). The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO: the mechanical and optical parts are derived from those of the ASTRI Mini-array, which is currently operating at the Teide observatory in the Canary island of Tenerife, while the Cherenkov focal-plane camera is an evolution of the CHEC-S SiPM (Silicon Photo-Multiplier) focal plane camera. In this contribution, we present the design and manufacturing phases of the mechanical structures of the SSTs. Since they are based on the heritage of the ASTRI telescopes, we describe how the original design of the ASTRI telescopes was modified, in order to improve the telescope performance, to host the SST Cherenkov camera, and to be compliant with the environmental, quality, interface, and safety requirements of CTAO. We also present the various phases of the manufacturing process, describing the details of each step (from the welding preparation up to the painting verification), and the formal inspections performed along it. Finally, we discuss the Quality Control Matrix used to perform the quality check of each manufacturing phase, and describe in detail the various types of test applied to verify the correct execution of the welding and painting phases.