NTT control/acquisition system as a prototype for the VLT

Abstract

The New Technology Telescope (NTT) installed at the Observatory of ESO, La Silla, Chile, employs a 3.5m active primary mirror and foresees that two instruments are mounted all the time at the Nasmyth foci. Remote observations from Germany will also be possible. The NTT is in many ways a prototype for ESO's Very Large Telescope (VLT), an array of four 8m telescopes now in the construction phase. This applies also to the control/acquisition system software, developed for the NTT, i.e. the software environment where specific control programs for telescope, adapters and instruments are running. Characteristic aspects of this system, which allows simultaneous multi instrument and multi-user operation, are described in this paper. The system is intrinsecally distributed both in hardware (several microprocessors on Ethernet) and in software (CPU independent program communication). System-wide information and complete decoupling of control programs from the user-end are obtained via a central parameters database (Pool) which supports data both on disc and memory, for time critical operations. This allows local and remote users to access in real-time all information on telescope and instruments without directly interfering with control programs. It permits also to have a truly open system with coherent expansion as soon as new modules are added. The distribution of the Pool on many CPUs and remote access methods will allow to develop a portable user-end for the remote use of the NTT and the VLT. This will be implemented on a workstation accomodating the user-end both for image processing and control and will be software configurable to act as a local control console of one or several telescopes and instruments or a remote observing tool useable from several astronomical Institutes in Europe.