The VISTA Telescope<sup>1</sup> is obtaining superb survey images. The M1 support system is essential to image quality and uses
astatic pneumatic supports to balance the M1 against the varying effects of gravity and wind, with four axes being
actively controlled via software and CANbus. The system also applies externally determined active optics force patterns.
The mechanical, electronic, software and control design and as-built operation of the system are described, with the
practical design points discussed.
Once it was decided that the VISTA infra-red survey telescope would be built on Paranal and operated by ESO it was
clear that there would be many long term advantages in basing the control system on that of the VLTs. Benefits over
developing a new system such as lower development costs or disadvantages such as constraints on the design were not
the most important factors in deciding how to implement the TCS, but now that the telescope is complete the pros and
cons of re-using an existing system can be evaluated.
This paper reviews the lessons learned during construction and commissioning and attempts to show where reusing an
existing system was a help and where it was a hindrance. It highlights those things that could have been done differently
to better exploit the fact the we were using a system that was already proven to work and where, with hindsight, we
would have been better to re-implement components from scratch rather than modifying an existing one.
VISTA is a 4-m wide field survey telescope with a near infra-red camera and a demanding f/1 primary design now well into its manufacturing phase. We contracted out major items, and generated a coordinated approach to the management of engineering budgets through systems engineering, risks through risk management, and safety through the generation of safety cases. Control of the interfaces and science requirements has been maintained and developed through the current phase. The project is developing the commissioning plan to deliver an effective and safe facility. The current status of VISTA is presented as we move towards the on site integration phase.
Data from the two IR survey cameras WFCAM (at UKIRT in the northern hemisphere) and VISTA (at ESO in the southern hemisphere) can arrive at rates approaching 1.4 TB/night for of order 10 years. Handling the data rates on a nightly basis, and the volumes of survey data accumulated over time each present new challenges. The approach adopted by the UK's VISTA Data Flow System (for WFCAM & VISTA data) is outlined, emphasizing how the design will meet the end-to-end requirements of the system, from on-site monitoring of the quality of the data acquired, removal of instrumental artefacts, astrometric and photometric calibration, to accessibility of curated and user-specified data products in the context of the Virtual Observatory. Accompanying papers by Irwin et al and Hambly et al detail the design of the pipeline and science archive aspects of the project.
The UKIRT Wide Field Camera (WFCAM) on Mauna Kea and the VISTA IR mosaic camera at ESO, Paranal, with respectively 4 Rockwell 2kx2k and 16 Raytheon 2kx2k IR arrays on 4m-class telescopes, represent an enormous leap in deep IR survey capability. With combined nightly data-rates of typically 1TB, automated pipeline processing and data management requirements are paramount. Pipeline processing of IR data is far more technically challenging than for optical data. IR detectors are inherently more unstable, while the sky emission is over 100 times brighter than most objects of interest, and varies in a complex spatial and temporal manner. In this presentation we describe the pipeline architecture being developed to deal with the IR imaging data from WFCAM and VISTA, and discuss the primary issues involved in an end-to-end system capable of: robustly removing instrument and night sky signatures; monitoring data quality and system integrity; providing astrometric and photometric calibration; and generating photon noise-limited images and astronomical catalogues. Accompanying papers by Emerson etal and Hambly etal provide an overview of the project and a detailed description of the science archive aspects.
VISTA is a wide-field survey telescope with a 1.6° field of view, sampled with a camera containing a 4 x 4 array of 2K x 2K pixel infrared detectors. The detectors are spaced so an image of the sky can be constructed without gaps by combining 6 overlapping observations, each part of the sky being covered at least twice, except at the tile edges. Unlike a typical ESO-VLT instrument, the camera also has a set of on-board wavefront sensors. The camera has a filter wheel, a collection of pressure and temperature sensors, and a thermal control system for the detectors and the cryostat window, but the most challenging aspect of the camera design is the need to maintain a sustained data rate of 26.8 Mb/second from the infrared detectors. The camera software needs to meet the requirements for VISTA, to fit into the ESO-VLT software architecture, and to interface with an upgraded IRACE system being developed by ESO-VLT. This paper describes the design for the VISTA camera software and discusses the software development process. It describes the solutions we have adopted to achieve the desired data rate, maximise survey speed, meet ESO-VLT standards, interface to the IRACE software and interface the on-board wavefront sensors to the VISTA telescope software.
The VISTA wide field survey telescope will use the ESO Telescope Control System as used on the VLT and NTT. However the sensors for both auto-guiding and active optics are quite different and so the ESO TCS will require some significant modifications. VISTA will use large format CCDs at fixed locations in the focal plane for auto-guiding and a pair of curvature sensors, also fixed in the focal plane, for wave-front sensing. As a consequence, three reference stars are required for each science observation in contrast to the VLT which uses a single star for both auto-guiding and active optics. This paper will outline the reasons for adopting this design, review how it differs from the VLT/NTT and describe the modifications that are being made to the ESO TCS to enable it to be used for VISTA. It will describe the software that implements auto-guiding and active optics in the VLT TCS and how the design has been adapted to the different requirements of VISTA. This will show how the modular and distributed design of the ESO TCS has enabled it to be adapted to a new telescope with radically different design choices whilst maintaining the existing architecture and the bulk of the existing implementation.
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 telescope's 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.
This paper describes the conceptual design for a near infrared camera for the Visible and Infrared Survey Telescope for Astronomy (VISTA). VISTA is a 4m class survey telescope that is being designed to perform pre-planned, ground-based astronomical surveys of the Southern sky from ESO's Cerro Paranal Observatory in Chile. The IR Surveys will be carried out in the J, H and K<sub>short</sub> wave-bands at fainter magnitudes than those produced by the current generation of survey telescopes. To maximise throughput and survey efficiency, the camera has been completely integrated with the overall optical design with the telescope mirrors providing the power and the camera optics the wavefront correction. The camera design employs a non-traditional approach to control stray light by using cryogenic baffles rather than the more traditional cold-stop approach. The very large optical field available, 1.6° diameter with a plate scale of approximately 57μm/arcsec, means that the focal plane can accommodate sixteen 2k×2k IR detectors thus forming the largest IR focal plane used in ground based astronomy to date. The 67 Mpixel focal plane will generate a significant data rate. Each exposure will comprise 270 MB and a typical night will generate 400 GB.