project Extremely Large Telescope (ELT)

The Europe Extremely Large Telescope (E-ELT) is the largest ground optical telescope project currently under construction in the world. With its sheer 39m in diameter, it will dwarf the largest telescopes of today. Such monster telescope required a lot of studies to prepare the actual construction phases.

Comparison between ELT and VLT (Chili)

AMOS is contributing in multiple ways to this mammoth project by providing expertise and hardware to help build this giant telescope.

System Engineering for the telescope main structure

ACe, an Italian consortium led by the company Cimolai S.p.A., won the contract for the Design, Manufacture, Transport, Construction, On-Site Assembly and Verification of the main telescope structure and for the dome of the observatory. AMOS has been involved in the project to support ACe engineering teams in some specific areas of expertise, mainly related to mechatronic and system engineering. ACe decided to integrate the expertise of AMOS into its design work. AMOS’ contribution includes estimating the impact of some design choices on the telescope final optical performance and supporting the design of the telescope main axes control system to ensure proper telescope movement and tracking. In addition, AMOS contributed to defining testing and integration activities related to some telescope critical items.

This contract, the biggest in ESO history, achieved in 2022 another major milestone. After the Dome and Auxiliary Building, AMOS’ contribution helped  ACe to successfully pass the Final Design Review of the Main Structure of the telescope.

Hardware for ELT

AMOS is also in charge of:

  • Polishing the reference body supporting the M4 deformable mirror of the telescope. This hard Silicon Carbide shell of 2.7m diameter has to be polished with a precision better than 15 um. The challenge is that unlike a uniform mirror, this piece is full of holes for the 5.000+ actuators, which makes the polishing but also he measurement of the shape of this piece a unique challenge.

    Reference body during final inspection.

  • Polishing two large tests mirrors for the test of the M4 deforable mirror system.

ELT’s Design Studies

AMOS also performed numerous studies to help define the ELT concept and convert it into an actual project.
The Extremely Large Telescope (ELT / ESO) will be the future 39 m diameter explorer of new astronomical frontiers in the next decade. On behalf of ESO, AMOS conducted two design studies addressing telescope subsystems.

M3 Unit design

The Tertiary Mirror Unit consists in a 4m-class mirror supported by an active mount. The purpose of this device is to correct every minute the mirror shape during the telescope tracking. The correction is applied by means of force actuators and aims at keeping an optimized telescope imaging quality.

M3 cell and M3 subunit

M4 – design support to CILAS

AMOS also worked on the design of the M4 unit support, as a partner of CILAS.

Study ELT pre-focal station

AMOS was contracted by ESO for the conceptual design of the ELT Pre-Focal Station (PFS) and its handling and tests facilities. The PFS is located on the Nasmyth platforms of the ELT. The so-called Pre Focal Station is a giant opto-mechanical multi-purpose system, which shall redirect the light beam having entered the telescope to the various analysing instruments of the focal plane.

The pre-focal station has the following functions:

  • sending the optical beam to the various instrumentation
  • monitoring the quality of the optical beam
  • de-rotate the telescope field.

The study consisted in the preliminary design of the pre-focal station in order to determine its future performance and characteristics.
The resulting design was a common framework structure containing 6 main units:

  • The axial rotator and the two lateral ones where instruments with a weight up to 5 tons are attached.
  • The common adaptor for 4 natural guide star and 4 laser guide probes equipped with wavefront sensors
  • The M6G&N unit where 2 mirror modules move in the same hoistway from their parking to their working position.
  • The M6C unit moving the M6C up from its parking position down to its working one.

Due to budgetary constraints, ESO had to reduce the scope of the pre-focal station. The PFS-A concept design is however largely inspired from that PFS design.

Published on 29.09.2022
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