Krister Wirenstrand

VLT telescope control software: an overview

The design of the VLT Telescope control software is driven by requirements of different nature and origin: technical/astronomical requirements, operational requirements, test and maintenance requirements, and general system engineering requirements. A driving factor is also the multitude of devices to be controlled and coordinated, which in itself leads to complications due to the large number of cases to be handled. The VLT Telescope control software will control and coordinate a large number of devices for each of the four 8 m telescopes, each with four individual foci, and additionally two combined foci. It is a requirement to support a large variety of observing instruments and procedures, some developed in-house, some by outside institutes and companies, and some still to be defined. The VLT control system is a highly distributed system; the control of devices is implemented in one VME unit for each device. All VMEs requiring accurate timing are also connected to the central time distribution system, which is of course a vital component in the tracking system. They are also connected to multiple LANs, to cope with different performance requirements. The use of a real-time database is an important design concept. A commercially available product is used (HP/Rtap), on which ESO has developed an additional layer of software that is used for all VLT application software. ESO has also developed a similar standard package for the VMEs that is compatible with the equivalent workstation layer. The paper describes different requirements and involved equipment, and it presents the main parts and characteristics of the software that should meet these requirements. The first part of the paper is an introduction to the telescope control part of the total VLT control system. Then there is a description of the environment and infrastructure on which the telescope control system is based, and finally a presentation of the telescope control software itself.

Applying VLT software to a new telescope: methods and observations

The VISTA wide field survey telescope will be operated and maintained from 2006 by ESO at their Cerro Paranal Observatory. To minimise both development costs and operational costs, the telescopes software will reuse software from the VLT wherever feasible. Some software modules will be reused without modification, others will include modifications or enhancements and yet others will be complete rewrites or completely new. This paper examines the methods used in the software development process to integrate existing and new software in a transparent and maintainable manner. On the basis of the work so far performed, some lessons are presented for the reuse of VLT software for a new telescope by an organisation without previous knowledge of VLT software.

Commissioning VLT unit telescopes: methods and results

The first VLT unit telescope, Antu, saw first light in May 1998 and started science operation in April 1999, roughly at the same time as first light of unit telescope 2, Kueyen, was achieved. The time between first light and science operation is used to verify, quantify, qualify and optimize the functionality and performance of the telescopes and their instruments.

The VLTI auxiliary telescopes: measured performances

The Very Large Telescope Interferometer (VLTI)1 that coherently combines the four VLT 8.2-m Unit Telescopes (UTs) is on the point to be fully equipped with its dedicated array of Auxiliary Telescopes (ATs). This array includes four 1.8-m telescopes which can be relocated on thirty observing stations distributed on the top of the Paranal Observatory. This array, albeit less sensitive than the array of UTs, is a key element for the scientific operation of the VLTI. Indeed, it will provide the best imaging capability thanks to the many possible baselines (up to 200m), it will be used for the Narrow Angle Astrometry mode which requires long term monitoring and the longest baselines not accessible with the UTs, and it will enable full-time use of the VLTI facilities even when the UTs are used for stand-alone observation. The Auxiliary Telescopes have been designed, manufactured and tested in Europe by the company AMOS (Belgium) under ESO contract. After acceptance in Europe, ESO takes over the responsibility for the transport to Paranal, reassembly and final commissioning. Currently the first three ATs have been put into operation on Paranal while the fourth one is scheduled to arrive at the observatory in August 2006. This paper presents the actual performances of the Auxiliary Telescopes, as measured during the commissioning of the first three ATs. An emphasis is given to the requirements dictated by the interferometer needs, including the ease and accuracy with which the telescopes can be relocated, the excellent image quality, and the nanometer-level stability for Optical Path Length.

VLT control software in its final test phase

The ESO VLT control software consists of all the software, which will be used to directly control the VLT Observatory and associated instrumentation. This is now in the implementation phase, performed to a large extent by ESO staff in the VLT software group. Consortia of Institutes responsible for some ESO instruments and contractors, who implement some of the telescope subsystems, are also involved. The main foundation body of the VLT control software, called VLT common software, is basically complete in its main functions. It has a size of about 500 K lines of code. This software is used in all the developments for the VLT telescopes and instruments and is distributed by ESO to all the collaborating consortia and contractors. The key components of the telescopes control software (TCS) have also been implemented. They make use of the VLT common software and have been field-tested in a first version in December 1995 at the ESO New Technology Telescope (NTT) in Chile. The NTT is being upgraded in parallel to the VLT development, using the same software. At the end of this conference a scheduled period of 6 months of site tests with the VLT main structure is going to start in Milan, Italy. This will allow us to perform hardware specific tests on this software. The Alt/Az axes control and hydraulics bearing subsystems are also part of the tests, which involve a set-up of two workstations and three VME/VxWorks based controllers. In parallel the first enclosure, including its software, is going to be accepted at the VLT site in Chile. This will mark the beginning of the control system implementation at the Paranal site. This paper gives an overview of the VLT control software, and describes its main components and characteristics.

Integration tests of the VLT telescope control system

The installation of the complete VLT telescope control system on the observatory is a complex task. It is important that the various components of the system have been carefully tested and integrated before. This paper presents the ESO strategy to pre-installation testing. In particular, results and experiences from pre-erection tests of the telescope structure are presented. In these tests, the complete telescope structure, including both axes with encoders and drives, has been built up at the premises of the European manufacturer (in Milan, Italy). These tests provide valuable input for the erection on Paranal. To this system, ESO added control electronics and software, which was tested with the telescope. The complete positioning of both main axes is under test, including slewing and tracking performance tests, as far as this is possible without using the sky. The VLT control software and most parts of the VLT control electronics have also been tested on the NTT on La Silla. Since the NTT upgrade software is practically a subset of the VLT software, the NTT tests have provided invaluable feedback for the VLT. The NTT tests are described in a separate paper presented at this conference. The paper also briefly discusses subsystem tests, and presents results from some of the subsystem tests performed in Europe.

VLT telescope control software installation and commissioning

This paper presents the actual status of the Telescope Control Software on the VLTs and on the other telescopes. The main focus is in the characteristics that make the TCS architecture portable on very different mechanical and optical configurations. Then the paper concentrates on the strategy used throughout the projects of integration and testing of the modular components. Particular attention is given to the installation and commissioning phases for the VLT telescopes.

Field stabilization on the ESO VLT telescopes

The Field Stabilization functionality compensates for image motions, mainly due to wind gusts, with a frequency of up to 50 Hz. Position errors are detected with a CCD mounted in the guide probe, and the correction vectors are passed to the secondary mirror, which can perform tip/tilt corrections with a frequency up to 100 Hz. This functionality is in regular use on the first two VLT telescopes, Antu and Kueyen; on Antu in operational use since 1st of April 1999 and on Kueyen for commissioning tests. In fact, Field Stabilization is ALWAYS used during observations. It is started as an integral part of the setting of the telescope. This paper describes the software and hardware that performs the Field Stabilization functionality. The architecture of the system, both software and hardware, is presented, with a discussion about problems and special solutions. The actual status, including some results from the commissioning and operational phases of the two first telescopes, is described. Finally, we present a short discussion about possible future extensions and improvements.

NTT control/acquisition system as a prototype for the VLT

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 ESOs 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.