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Harness & Piping...Reaching every part!

13/12/2005

Harness and Piping are the names of two cartoon characters - soon you will be able to hear them! We have created them to tell you about the channels, cables and pipes that are needed in an instrument like the Gran Telescopio CANARIAS (GTC).

If we asked you about a system that transports nutrients, oxygen and blood around the body, you would immediately think of veins and arteries.

Well, the veins and arteries of the GTC are the cables, pipes and conduits that will connect up everything that needs to be connected. They will come from the different parts of the enclosure - the oil pumping room, water coolers, air compression system, helium compressors, control systems, electricity supply units and so on - that are spread throughout the GTC.

All of these conduits will be concentrated in the telescope pier, from where they will head out to terminal points - electronics cabinets - sited throughout the length and breadth of the telescope. The most important of these cabinets are at the two Nasmyth platforms, the rotating floor and the primary mirror cell.

A number of design problems have had to be overcome to make all of this possible: First, the difficult geometry of the telescope; second, the lack of space; and third, the need to connect moving parts to other moving parts. In other words, not only do we have to install the 'veins' at strategic points - we also have to avoid them becoming tangled, mixed up or twisted. To do this, the telescope has been designed with cable rotators. These will make sure that the cables stay in the right place and avoid them becoming tensed, which could affect the movement of the telescope.
The GTC will have three types of cable rotator, corresponding to the three degrees of freedom of the telescope's movement: one for the azimuth axis, another for each of the elevation axes, and a third for the instrument rotators.

The 'veins and arteries' will carry compressed air, electricity, water, fibre optics and helium. Let's take each one in turn.

Why do we need compressed air? It will basically be used to keep delicate surfaces clean and dry. The compressed air will pass through filters to clean it, driers to ensure it is very dry, and a compressor to make it come out under pressure. It will circulate through flexible hoses that will be joined to various connecting and binding devices, distribution collectors and measuring equipment like manometers to monitor pressure and thermometers to monitor temperature.

Water: This will be used to cool parts that could become hot. It will be carried in two different circuits, one at the ambient temperature and another at 5º C. Why is this? Well, the temperature difference between the water at 5 ºC and the exterior could cause condensation. For this reason the piping is insulated with elastomeric foam, a product that limits heat transfer. However in some places there will be no insulation and, to avoid condensation, the water will have to be at the ambient temperature. The maximum diameter of the interior of the hoses will be 3cm. The diameter of the exterior, including the insulation material, will be up to 9cm.

Electricity: We will have four electrical circuits. The first is the normal network (just like you find in a house). The second is called the 'group network'; when necessary, it can be supplied by the generator or the auxiliary generator. The third circuit is similar to the previous one, but will supply a 'cleaner' or more stable current. The fourth circuit is called the UPS (Uninterrupted Power Supply): It will provide an uninterrupted electricity supply from batteries if the other systems fail. The circuits will be made up of cables, protected distribution panels (with magnetothermic circuit-breakers and differentials which, like in a domestic system, will provide protection from electricity surges in the network). They will be earthed so that, should there be a power surge, the electricity will be directed to the base of the enclosure or "earth ring".

Helium: This will be needed to cool the science instruments. It will come out of the compressor and will expand when it reaches its destination, causing the temperature to drop. The conduits through which it will travel are similar to those used for the water, but they will be made using special materials and soldering to ensure cleanliness and prevent leaks in the circuit (helium gets everywhere!).

Fibre optics: These are delicate and sensitive and so must not be bent too much. They will be used to carry data throughout the system and will be like parts of a neuron network. Each hose will be able to carry 24 to 48 fibre 'hairs'.

In total we will have 2,000 metres of pipes or hoses and some 3,000 metres of cable. Metres and metres of veins to feed the telescope.

Natalia R. Zelman

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