Communiqué de presse
Le miroir secondaire de l’ELT a été moulé avec succès
L’ébauche du plus grand miroir convexe jamais conçu
22 mai 2017
L’ébauche du miroir secondaire de l’ELT (télescope géant) a été réalisée par la société SCHOTT basée à Mayence en Allemagne. Lorsque finalisé, ce miroir sera caractérisé par un diamètre de 4,2 mètres et une masse de 3,5 tonnes. Il sera alors le plus grand miroir secondaire jamais installé sur un télescope ainsi que le plus grand miroir convexe réalisé à ce jour.
Avec ses 39 mètres de diamètre, le Télescope géant (ELT pour Extremely Large Telescope) de l’ESO sera le plus grand télescope de son genre jamais conçu lorsqu’il captera sa première lumière en 2024. Le moulage du miroir secondaire du télescope (M2), dont les dimensions excèdent celles de la plupart des miroirs primaires équipant les télescopes scientifiques actuels, constitue une nouvelle étape de sa réalisation.
L’ébauche du miroir consiste en un moulage du matériau – du vitrocéramique Zerodur® [1] – destiné à être taillé puis poli afin de donner naissance au miroir final. En janvier 2017, l’ESO a attribué à l’entreprise SCHOTT le contrat de fabrication de l’ébauche du miroir M2 (eso1704). L’ESO s’est réjoui d’une collaboration fructueuse avec SCHOTT, choisie par le passé pour produire les miroirs principaux du ménisque de 8,2 mètres de diamètre du Very Large Telescope à l’Observatoire de Paranal de l’ESO (ann12015). En tant que fabricant de produits astronomiques d’exception et de qualité supérieure, SCHOTT a déjà livré les ébauches des miroirs déformables de faible épaisseur qui constitueront le miroir quaternaire de l’ELT, M4 (ann15055), et fournira l’ébauche du miroir tertiaire M3.
L’ébauche du miroir secondaire doit à présent subir un lent refroidissement, faire l’objet d’un usinage puis d’un traitement thermique au cours de l’année à venir. Il sera prêt alors à être taillé puis poli. Telles seront les missions de la société française Safran Reosc. En outre, cette dernière procèdera à des tests complémentaires (ann16045). Le moulage sera taillé et poli à la précision de 15 nanomètres (15 millionièmes de millimètre) sur la totalité de la surface optique.
Une fois achevé et installé, le miroir M2 sera suspendu au-dessus du vaste miroir primaire du télescope et constituera le second élément du système optique novateur à cinq miroirs de l’ELT. Le miroir est fortement courbé et asphérique. Sa réalisation ainsi que l’accomplissement de divers tests constituent donc de réels défis techniques.
Notes
[1] Développé à l’origine pour les télescopes astronomiques conçus à la fin des années 1960, le Zerodur® ne présente quasiment aucune dilatation thermique lorsqu’il est soumis à d’importantes fluctuations de température, il est hautement résistant chimiquement parlant, et peut être poli avec une précision élevée. De nombreux télescopes dotés de miroirs Zerodur® ont parfaitement fonctionné des dizaines d’années durant, au premier rang desquels le Very Large Telescope de l’ESO au Chili.
Liens
Contacts
Marc Cayrel
ESO
Garching bei München, Germany
Tél: +49 89 3200 6685
Courriel: mcayrel@eso.org
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tél: +49 89 3200 6655
Mobile: +49 151 1537 3591
Courriel: rhook@eso.org
Joerg Gasser (contact presse pour la Suisse)
Réseau de diffusion scientifique de l'ESO
Courriel: eson-switzerland@eso.org
A propos du communiqué de presse
| Communiqué de presse N°: | eso1715fr-ch |
| Nom: | Extremely Large Telescope |
| Type: | Unspecified : Technology |
| Facility: | Extremely Large Telescope |
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