The basic function of the pier is to support the telescope and the enclosure. It forms the connection between telescope/enclosure and ground. At the bottom of the pier the instrument (Coudé) room is located, which has dimensions of approximately 16 m x 10 m (diameter x height) and influences on the design of the pier. The pier is divided into two parts: a lower and an upper pier. The lower part houses the instrument room; the upper part accommodates the transfer optics.
The error budget specifies three values for the pier. The first is the budget for thermal aspects, and specified as a contribution to image blur of 0.038". The second is the budget for windshake, which is defined as: 1.0" pointing accuracy for wind and 0.2" tracking accuracy for wind (10 minute interval). Finally, the thermal stability should be better than 0.5" pointing accuracy for thermal effects and 0.1" tracking accuracy for thermal effects (10 minute interval).
The proposed design incorporates a cone-shaped pier top, which is the stiffest pier design. At the top, the diameter was derived from the size of the azimuth bearing of the telescope and transfer optics. Around the cone a steel framework is erected that supports the enclosure platform. Together they form a good alternative for reducing pier seeing.
The height of the pier is set at 38 m. It leads to a design where the instrument lab is above ground level, with only a service floor level underground. This height of 38 m is also the largest height that a local mobile crane can reach. The final design has a cylindrical base that surrounds the instrument lab. A cylindrical base fits better to the building, otherwise also a complete cone could be chosen. Around the top of the pier a ø33 m steel platform is located. The preference is to attach the building to the pier, with some of the facilities housed inside the pier. There is no indication from the CFD analysis that the building has a negative impact on the generated turbulence, since it is well below the telescope level.
The framework is bolted together on site, all elements dip zinc and TiO2 coated. After assembly the construction is maintenance free and does not need periodic repainting.