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Stiffness analysis for a giant telescope (VLT)
ESO has developed the GALACSI adaptive optics module for the Very Large Telescope (VLT) in Chile. CADFEM used simulation to test the stiffness.

Stiffness analysis for testing the reliability of optical instruments

Sector: Machinery and plant engineeringSpecialist field: Structural mechanics

The GALACSI adaptive optics module, built by ESO engineers at the Garching headquarters, is part of the Very Large Telescope (VLT) on Cerro Paranal in Chile. Before its deployment, the stiffness of the optics was tested with simulation tools from Ansys and expertise from CADFEM.

Summary

Task

On a giant telescope (VLT), bending stresses can occur on the optical system (mirrors/lenses) due to environmental conditions (gravity, earthquakes, temperature fluctuations). These would significantly affect the performance of the system.

 

Solution

To ensure the reliability of the sensitive structures, the stiffness behavior of the GALACSI module was determined using ANSYS® Workbench™.

Customer benefits

By introducing the required optical coordinate systems into the FE environment, an efficient post-processing of the system behavior was achieved.

Project Details

Task

GALACSI is an adaptive optical module containing multiple wavefront sensor cameras, relay optics, electronics, and the necessary mechanical systems. The entire structure is mounted on one of the Very Large Telescopes (VLT) at the Paranal Observatory in Chile. On such a giant telescope, bending stresses can occur on the optical system (mirrors/lenses) due to environmental conditions (gravity, earthquakes, temperature variations). These would significantly affect the performance of the system. The reliability of the sensitive structures had to be tested in advance.


Customer Benefit

Based on these results and the sensitivity matrix provided, ESO was able to analyze and evaluate the image stability of the system. By introducing the required optical coordinate systems into the FE environment, efficient post-processing of the system behavior was achieved.


Solution

To ensure the reliability of the sensitive structure, the stiffness behavior of GALACSI was determined using ANSYS® Workbench™. For this purpose, a finite element model of the support structure was created based on solid elements. Optical components, or subsystems, were idealized at the position of their optical points with point masses attached to the respective attachment points. Third-party components (e.g., drives) were simplified using stiffness values from their data sheets. Bending stresses and frequencies were calculated for various possible configurations. The displacements and rotations of the optical points were exported with respect to the orientation of the optical paths.

Images: © ESO (European Southern Observatory)


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