6 July 2018 MELT: an optomechanical emulation testbench for ELT wavefront control and phasing strategy
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Abstract
We present an optomechanical test bench setup (MELT) for testing and validating key functionalities to be used on the Extremely Large Telescope (ELT) during the periods of system verification, wavefront control commissioning, through the handover to science, up to regular diagnostic, monitoring, and validation tasks during operations.

The main objectives of MELT are to deploy and validate the telescope control system, to deploy and validate wavefront control algorithms for commissioning and operations, as well as to produce and validate key requirements for the phasing and diagnostic station (PDS) of the ELT.

The purpose of MELT is to deploy optomechanical key components such as a segmented primary mirror, a secondary mirror on a hexapod, an adaptive fourth mirror, and a fast tip/tilt mirror together with their control interfaces that emulate the real telescope optomechanical conditions. The telescope control system, deployed on MELT can test control schemes with the active mounts emulating the real ELT optomechanical control interfaces.

The presented optomechanical setup uses the Active Segmented Mirror (ASM) with its piezo-driven 61 segments and a diameter of 15 cm. It was designed, built, and used on sky during the Active Phasing Experiment (APE).

Several beam paths after the telescope optical train on MELT are conditioned and guided to wavefront sensors and cameras, sensitive to wavelength bands in the visible and infrared to emulate wavefront commissioning and phasing tasks. This optical path resembles part of the phasing and diagnostics station (PDS) of the ELT, which is used to acquire the first star photons through the ELT and to learn the usage and control of all the ELT optomechanics. The PDS will be developed, designed, and built in-house at ESO. MELT helps its design by providing a detailed test setup for defining and deploying system engineering tasks, such as detailed functional analysis, definition of tasks to be carried out, and technical requirements, as well as operational commissioning aspects.

The bench test facility MELT will in the end help us to be as much as possible prepared when the telescope sends the first star light through the optical train to be able to tackle the unforeseeable problems and not be caught up with the foreseeable ones.
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
T. Pfrommer, T. Pfrommer, S. Lewis, S. Lewis, J. Kosmalski, J. Kosmalski, P. La Penna, P. La Penna, C. Frank, C. Frank, I. Guidolin, I. Guidolin, S. Leveque, S. Leveque, A.-L. Cheffot, A.-L. Cheffot, H. Bonnet, H. Bonnet, N. Kornweibel, N. Kornweibel, J. Spyromilio, J. Spyromilio, "MELT: an optomechanical emulation testbench for ELT wavefront control and phasing strategy", Proc. SPIE 10700, Ground-based and Airborne Telescopes VII, 107003F (6 July 2018); doi: 10.1117/12.2313537; https://doi.org/10.1117/12.2313537
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