E-ELT MAIN STRUCTURE
The telescope structure is an alt-az mount (see Figure 1) and it is
divided into two main parts: the Azimuth Structure and the
Altitude Structure. The main structure, including the hosted units and the
items intended for operational use, weighs about 2800 t.
Two massive cradles provide the
rotation of the altitude axis while the azimuth tracks
allow the rotation of the telescope about the zenith. The
challenge in such a massive design is to provide a stiff enough
interface for the primary mirror segments, while at the same time not
dramatically increasing the weight of the structure or
overcomplicating the support. Scaling the size of M1 to the current dimensions has made it possible
to achieve a lighter, stiffer and more compact telescope structure.
The azimuth structure (see Figure 2) supports the scientific instruments. It
rides on three azimuth rings, of 51.5-m, 34-m and 4.5m diameter.
The two biggest rings
support the main vertical reactions during all operational modes. The radial loads
are supported by the intermediate ring, while the central ring supports part of the
The azimuth structure is made of hollow members and weighs about 1300 t.
The altitude structure (see Figure 3) hosts the telescope optics. It is made of hollow beams and is estimated to weigh approximately 1500 t with the hosted units. The major challenges that have been addressed in the design are the need to keep the primary mirror segments within a reasonable range from their prescribed locations and the need to minimize the deflections of the secondary mirror.
As shown in Figure 3, the large central obstruction of the optical design also provides ample room for the erection of a central tower (see also Figure 4). This tower supports M3, M4 and M5, together to the Atmospheric dispersion compensator (ADC) and the adaptive optics calibration unit (CU). The CU creates artificial sources at the side of the central tower and projects them on a small mirror positioned close to M4. An optomechanical relay system inserts the source light beam inside the telescope train when the CU is in operation.
Figure 1. Main structure
Figure 2. Azimuth structure
Figure 3. Altitude structure
Figure 4. Central tower