Title
Dynamic testing of primary mirror segment supports for the Extremely Large Telescope
Author
Witvoet, G.
Nijenhuis, J.R.
Kramer, L.
Contributor
Marshall, H.K. (editor)
Spyromilio, J. (editor)
Publication year
2018
Abstract
The preparations for the design and construction of the Extremely Large Telescope (ELT) are in full swing. One of the most critical components of this enormous telescope is its segmented primary mirror (M1), for which Netherlands Organisation for Applied Scientific Research (TNO), in collaboration with VDL, has designed the mechanical segment support (M1SS) in the period 2015-2016.1 This new M1SS design is based on the previous M1SS prototypes developed in 2009-2010,2 but includes several enhancements to further improve its performance. Specific design drivers were, among others, the serviceability of the M1SS, the introduced surface form error at the segment, and the increased target values for the structural eigenfrequencies. The latter defines the dynamic performance of the structure (including the ∼178 kg segment), which needed to be validated experimentally. From the latest M1SS design one engineering model (EM) and six qualification models (QMs) have been manufactured recently, which have tested intensively to verify their performance. This work will present the test procedure employed to validate the dynamic behavior, describe these dynamic tests and present their results in detail. During these tests a QM, including a dummy segment, has been placed on a heavy rigid structure and three accelerometers have been mounted across the assembly. The structure has then been excited on several strategic locations using a roving hammer technique,3 resulting in a large collection of frequency responses. From these, the eigenfrequencies and accompanying mode shapes have been estimated, resulting in accurate determination of the clocking, lateral, piston and tip/tilt modes of the structure. This allows for correct assessment of the dynamic performance and comparison to the design objectives and finite element model (FEM) predictions. This procedure has been applied to two different QMs, but since each M1SS consists of a fixed frame (FF) and a removable segment assembly (SA), four different configurations have been tested. The results demonstrate compliance with the challenging design objectives for all QMs, and they show only small variations among the configurations, demonstrating that the dynamic performance of the M1SS design is very reproducible.
Subject
High Tech Systems & Materials
Industrial Innovation
ELT
Segment support
Airborne telescopes
Dynamic analysis
Frequency response
Machine design
Mechanisms
Optical telescopes
Optical testing
Rigid structures
Extremely Large Telescopes
Primary mirror segments
Qualification model
Scientific researches
Segmented primary mirrors
Strategic locations
Structural design
To reference this document use:
http://resolver.tudelft.nl/uuid:8a91dc1c-2fa8-4d43-b50b-bb5f35b4e386
TNO identifier
842190
Publisher
SPIE
ISBN
9781510619531
ISSN
0277-786X
Source
Ground-Based and Airborne Telescopes VII 2018, 10-15 June 2018, Austin, TX, USA, 10700
Series
Proceedings of SPIE - The International Society for Optical Engineering
Article number
107003J
Document type
conference paper