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October 2, 2023



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The last piece...


As you will see, it looks like a spider with six or twelve legs (depending on how you look at it) supported by a hexagon. This hexagon is the ring, which is made up of six pairs of supports with a space in the middle for the secondary mirror and its control system.

It is the last piece in the structure of the Gran Telescopio CANARIAS (GTC): the secondary mirror spider.

It is connected to the upper part of the tube by the ring and will carry the weight of the entire secondary mirror structure, which is made up of the mirror and its control systems. The secondary mirror structure weighs 12 tonnes: the spider itself weighs some 10,000 kg and will hold up a mass of 2,500 kg 20 metres high. Yet the stress caused by all this weight will compress the spider by just 300 microns or less.

To reduce the shadow cast by the spider, its supports will be narrow and positioned over the gaps between the segments of the primary mirror.

This is the last piece in the mechanical structure of the telescope: first, the azimuth ring was installed, then the mount, and finally the tube – crowned by the spider. Three hundred tonnes of carbon steel which will now undergo a process of adjustment and alignment.

Natalia R. Zelman

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