In order to make the most efficient use of the VLTI each night, four smaller, dedicated ‘Auxiliary Telescopes’ (ATs) are available. The ATs are mounted on tracks and can be moved between precisely defined observing positions. From these positions, their light beams are combined in the VLTI.
The ATs are very unusual telescopes. In their ultra-compact protective domes, these 33-ton machines carry their own electronics, ventilation, hydraulics and cooling systems. Each AT has a transporter that lifts the telescope and moves it from one position to the other. Almost like a snail, it moves around with its own housing.
The Auxiliary Telescopes have rather unusual characteristics:
    - they are relocatable,
    - they are totally self-sufficient with only electrical connections to the site,
    - they carry their own dome and cooling and ventilation systems and do not need additional environmental protection,
    - they must fulfil the very stringent mechanical stability requirements imposed by interferometry at the level of a few tens of nanometres.
Since the new ATs are moveable, the entire configuration of telescopes can be changed according to the observational requirements.
Control Room
Unit Telescopes