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September 24, 2023



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Round and round and round


David and Goliath in one. The precision, ingenuity and carefulness of the most advanced engineering face to face with enormous components, so heavy you would think that moving them at these levels would be impossible. The task is to work with precision and in minute detail on colossal objects, to move 850 tonnes with the ability to point at a vehicle 1000 kilometres away and without a single vibration.

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Once built, anyone confronted with the sheer size of the telescope (41 metres high) might think that the Gran Telescopio Canarias (GTC) looks like a clumsy giant, but nothing could be further from the truth. Every component has been designed for perfect operation to ensure that everything turns with microscopic precision. This is why, like trains, the dome will rotate on rails.

If you wanted to find out how a railway track is built you would need to visit a rail construction site, or watch a Western showing railway building in the wild frontier! However, to find out how the GTC’s rails were installed you just need to read on…: the rails look the same as the ones used by trains, but, as you would expect, making and installing them will call for more accurate technology.

Precision is not exactly compatible with size: screws half a metre long and several centimeters in diameter join the girder to the concrete base, whilst huge clamps will hold the girder to the rail…these are rails for a “train” that will journey through time, amongst the stars.

The rail girder

The rail girder will support the complex framework on which the dome will rotate; it will be made up of 12 parts, each with an angle of 30 degrees, around 19 centimetres tall and 37cm wide. The girder will be held in place by means of holes, called ‘pockets,’ in the concrete wall. These holes will be over half a metre (58cm) deep, with a diameter of 15cm at the top and 12cm at the bottom (they will be shaped like an upside-down cone).

The sections of rail girder will be joined together by 8 screws, each 1.6cm in diameter and 7cm long. To attach the girder to the concrete wall, screws or pins will be sunk into the ‘pockets’ which will then be filled with mortar to the level of the regulating nuts.

Careful planning will ensure that these nuts can be used to correct any unevenness in the rail girder after installation. After correcting for any deviations, the holes will be filled to the top with mortar.

Clamps are then attached to the girder to hold the rail in place in a special way: they are designed not to pin the rail down, but to allow it to travel freely upwards, up to a certain point, and then to “grab” it if it continues. This will aid the distribution of weight over pieces rubber called interspersers, which will be fitted between the girder and the rail and are designed to reduce vibration and spread the weight of the dome.

This is how the GTC’s rails will be installed. We will tell you more about it in future editions of the Bulletin.

Natalia R. Zelman

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