Final tests of the VLT main telescope structure (1997)

The main structure of the VLT was designed, produced and assembled by an Italian consortium composed of Ansaldo Energia (Genova), European Industrial Engineering (Venice) and SOIMI (Milan). A total of four identical structures were built, one for each of the four VLT 8.2-m Unit Telescopes.

Here, the VLT mechanical structure for Unit Telescope 4 (UT4) is seen during the tests at the Ansaldo Factory in November 1997.

The movable part of the telescope structure weighs 430 tonnes. It is composed of an azimuthal structure (the telescope fork) which moves on two concentric tracks on oil pads, and of an altitude structure (the telescope tube), also moving on oil pads.

Despite its enormous size and weight, the dimensions of the telescope structure must be extremely accurate and stable. For instance, the stability of the oil film was measured to be better than 100 nm (0.0001 millimetre) over 1 minute. This excellent value was well within the specifications and has contributed to the subsequent near-perfect optimization of the telescope's tracking performance.

The first of the four telescope structures (for UT1) was transported to Paranal already in early 1997.