Kick-off meeting for the preliminary design of the EST secondary mirror

The EST Project Office and the Dutch engineering company TNO held a virtual meeting on April 16, 2021.

CAD render of the EST adaptive secondary mirror. Image credit: TNO/ R. Hazelebach

The EST Project Office and TNO held a meeting on April 16, 2021 to start the design works for the EST adaptive secondary mirror (M2).

The industrial contract was awarded to TNO. This company has long experience in developing state-of-the-art adaptive mirrors for telescopes, like the UH88 telescope in Hawaii and others owned by the European Space Agency and the University of California’s Center for Adaptive Optics. TNO will partner with the company VDL ETG, in charge of providing high-precision actuators. The total amount of the contract is 495.000 EUR.

This is the third contract awarded as a result of the call for tenders issued in August 2020. The other two contracts are devoted to the preliminary design of the telescope structure, pier and enclosure, and the primary mirror assembly. The next telescope sub-system to be tendered will be the heat rejecter.

Scope of the contract

During the next 78 weeks, TNO will design the adaptive secondary mirror according to the requirements set forth by the project. The objective is to consolidate the baseline solution identified for EST.

Specifically, the main tasks to be performed during the contract are:

• Design of the M2 assembly and the auxiliary equipment for handling, maintenance, calibration and operation.
• Validation of the design by modelling and analysis.
• Verification of the key components of the M2 assembly by a test campaign on breadboards and prototypes.
• Definition of a production plan and schedule for the M2 assembly, including detailed design, manufacturing and AIV.
• Definition of a production cost estimate for the M2 assembly, including detailed design, manufacturing and AIV.

TNO shall develop his own Front-End Engineering and Design of the M2 assembly assuming the requirements defined in the preliminary design.

The EST M2 assembly

The EST adaptive secondary mirror is a 800 mm diameter concave ellipsoid which defines the telescope pupil. It will be located after the field stop, so the amount of light reaching M2 is exactly that of the desired field of view: one and a half arc minutes.

M2 will be equipped with two correction mechanisms. The first one will compensate the vibrations produced by the wind. This will be achieved with fast, large amplitude tip-tilt motions of the mirror to make the image as still as possible.

The second mechanism is intended to correct the image distortions caused by atmospheric turbulence. To that end, the mirror will be deformed by hundreds of actuators placed at its base. These actuators exert forces, producing both longitudinal displacements and tilt-tip rotation of the mirror surface. This correction is an integral part of the EST multi-conjugated adaptive optics system, of which M2 will be the first mirror.

The use of an adaptive secondary mirror greatly simplifies the optical system, reducing the number of mirrors from 14 to only 6 plus a doublet lens. This, in turn, will result in a much larger photon throughput with 50% more light.

Participants in the virtual kick-off meeting.

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