The VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at
Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The
VST is a wide-field imaging facility planned to supply databases for the ESO
Very Large Telescope (VLT) science and carry out stand-alone observations in
the UV to I spectral range. This paper will focus mainly on control software
aspects, describing the VST software architecture in the context of the whole
ESO VLT control concept. The general architecture and the main components of
the control software will be described.Comment: 3 pages, 2 figures, ICALEPCS 2001 Conference, PSN#THAP05

Brescia, M.

Mancini, D.

Marty, L.

Schipani, P.

Spirito, G.

English

arXiv

The VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus mainly on control software aspects, describing the VST software architecture in the context of the whole ESO VLT control concept. The general architecture and the main components of the control software will be described...

Schipani, Pietro

Brescia, Massimo

Mancini, Dario

Marty, Laurent

Spirito, Gianfranco

Archivio della ricerca - Università degli studi di Napoli Federico II

THAP051THE VST TELESCOPE CONTROL SOFTWARE IN THE ESO VLTENVIRONMENTP. Schipani, M. Brescia, D. Mancini, L. Marty, G. SpiritoOsservatorio Astronomico di Capodimonte, Napoli, ItalyAbstractThe VST (VLT Survey Telescope) is a 2.6 m Alt-Aztelescope to be installed at Mount Paranal in Chile, inthe European Southern Observatory (ESO) site. TheVST is a wide-field imaging facility planned to supplydatabases for the ESO Very Large Telescope (VLT)science and carry out stand-alone observations in theUV to I spectral range. This paper will focus mainly oncontrol software aspects, describing the VST softwarearchitecture in the context of the whole ESO VLTcontrol concept. The general architecture and the maincomponents of the control software will be described.1 ARCHITECTURE1.1 Maintenance requirementsThe VST telescope will be installed at Cerro Paranalin the Atacama desert, Northern Chile, as a powerfulsurvey instrument for the largest ground-basedtelescope of the world, the ESO VLT. It is a jointproject between the Osservatorio Astronomico diCapodimonte (OAC) and ESO. OAC has beencommitted to design and install the telescope, softwareincluded, but after the installation and commissioningVST will be managed by ESO staff. Therefore in orderto simplify the future maintenance of the software byESO staff, the easiest way is to develop the VSTsoftware in the most “VLT-compliant” way.Figure 1: VST in the Paranal observatory  (ESOcourtesy, http://www.eso.org)1.2 General architectureAs the VLT is a large project involving many staffpeople for many years, strong standardization has beenintroduced by ESO in the software development andhardware platforms.The VST software is based on the same standardarchitecture: distributed workstations running HP-UXand VME-bus-based Local Control Units (LCU)running the VxWorks real time multitasking operatingsystem, connected together via Local Area Networks. LCUs interface with field electronics and electro-mechanics, driving encoders, axis controllers, limitswitches, etc.; the application software they run is a lowlevel software program, used to control and monitor thehardware devices.The workstations coordinate LCUs and run thegraphical user interfaces (GUI), running high levelapplication software; this kind of software has timeexecution requirements less urgent than the LCU’s one,and is the one the operators usually interface with.The basic ideas in the architecture are modularityand standardization. Each LCU is devoted to a specifictask, so the hardware devices are driven independentlyby different LCUs, but they use whenever possible thesame VME boards and the same software.The programming languages on HP-UX platform areC++ for the core control modules, and Tcl/Tk forgraphical user interface development. The Tcl languageis interpreted, so Tcl applications normally do not runas fast as equivalent C programs. However, for a largeclass of applications, this is not a disadvantage sincethe processing speed of modern computer systems ismore than adequate. The LCU modules are developedin C.A key role in both workstation and LCU softwarearchitecture is played by an On Line Data Base, whichon-line allows sharing information between modules,monitoring the status of the system and the execution ofcommands. The database is built using HP RTAP (RealTime Application Platform), available on HP-UXworkstations. RTAP is a modular, Unix based softwareplatform for real-time data acquisition and control ofcontinuous processes. It is a Supervisory Control andData Acquisition (SCADA) system.Between the operating system and the applicationlayer there is a software layer developed by ESO forVLT which is reused for VST, the VLT CommonSoftware, providing a lot of utilities, tools and commonservices to the application programmer.2 TELESCOPE CONTROLSOFTWARE2.1 IntroductionThe VST Telescope Control Software (TCS) is thesoftware package responsible for:• Control and monitoring of the telescope• Interface to users and other VST softwarepackages• Interface  to star catalogues2.2 Module structureEach TCS module is provided with a CommandDefinition Table (CDT) which is normally used for allinter-module communications and is also used by theTCS user interface panels.In the TCS general module architecture all themodules are implemented through one or moreindependent processes. If a module is made up of morethan one process only one of them is the “control”process which provides the public interface, receivescommands from other modules and sends back thecorresponding replies. In order to respect theserequirements every process is designed in an event-driven way and the implementation is based on theevent-handler design. The TCS package is composedby several modules associated to the telescopesubsystems to be handled. Each module is organized in processes and functionsdedicated to the LCU and/or WS resident applications.The applications use specific commands to perform allthe actions foreseen for the control and management ofthe associated subsystem.2.3 TCS: VST vs VLTDue to the maintenance requirements, there is acommitment to the VST team in agreement with ESO,to re-use as much as possible the existing VLTTelescope Control Software.Since VLT and VST have many similarities in thecoordination and control but are very different in manyhardware solutions (they have very different size andscientific purposes), this is usually much more possiblein the workstation part than in the LCU one, whichhighly depend on the hardware used in the controlleddevices.The main physical devices to be controlled actuallyare:• azimuth• altitude• Cassegrain instrument rotator• hydrostatic bearing support system• motor cooling system• adapter• probe• focusing device• pick-up mirror• atmospheric dispersion corrector• two-lens corrector• guiding camera• Shack-Hartmann device• M1 support system• M2 support systemComparing the VST mechanical and hardwaresolutions with the VLT ones device by device (andconsidering there are some new devices in VST notpresent in VLT) it becomes clear that in the LCUsoftware the percentage of the VLT TCS  that can bereused is very low, because the differences are often solarge that it is convenient to re-write the relatedsoftware modules from scratch. The leading concept isthat wherever possible the interface (i.e. the CommandDefinition Table, see 2.2) with the outside world of thenew LCU modules is structured in order to becompatible with the existing and reusable (when this isthe case) workstation modules. A couple of examplesare briefly described in the following.2.4 The case of M1 pad controlOne of the VST subsystems whose hardware iscompletely different from the VLT one is the M1 padcontrol system. The primary mirror is supported by 84axial and 24 radial pads. The mirror sag can bemodified applying a set of forces to the astatic levers inorder to correct 3rd and 4th order aberrations as in theactive optics scheme usual in  the new generation oftelescopes.The control system used in VST to implement thepad control is based on a CAN bus network of customdeveloped microcontroller boards. The introduction ofCAN bus is a new feature for the Paranal observatory,so there were no standards to follow either forhardware or software. Consequently the softwaremodule to exchange information with the astatic levercontrollers, following an established communicationprotocol, is completely new, even if developedfollowing the same structure and general rules of all theother modules.TCSWorkstationLCUAzimuthLCUAltitudeLCUM1, M2LCURotator/Adapter/ADCLCUHBSInternal RouterGuide/AcquisitionWorkstationLCUGuiding ControlLCUImage AnalysisFigure 2: Telescope Control Architecture2.5 The case of Atmospheric DispersionCorrector controlThe atmospheric dispersion correction in VST isobtained actually using two different optical correctors,user selectable depending on the altitude angle: they arenamed “ADC” and “2-lens corrector”. The ADC iscomposed by two rotating pairs of prisms, while the 2-lens corrector optics positions are fixed.Here the difference with VLT basically in the usageof two different correctors, in the kind of  motion(circular and not linear) of the optics, in the algorithmto calculate the prism positions, and in the kind of theselected motors. Therefore even if at first glance thereare many similarities in the two systems, the LCUmodules must be completely different, and theworkstation module needs some modifications. Again,the old interface between modules (CDT) can belargely saved, and extended with new features whereneeded.3 REFERENCES[1] D. Mancini, G. Sedmak, M. Brescia, F. Cortecchia,D. Fierro, V. Fiume Garelli, G. Marra, F. Perrotta,P. Schipani, : 2000, “VST project: technicaloverview”, in “Telescope Structures, Enclosures,Controls, Assembly / Integration / Validation, andCommissioning”, eds. Sebring, T., Andersen, T.,SPIE, 4004, pp. 79-90[2] D. Mancini, G. Sedmak, M. Brescia, F. Cortecchia,D. Fierro, V. Fiume Garelli, G. Marra, F. Perrotta,P. Schipani, : 2000, “VST Final Design Review”,http://vst.na.astro.it

The VST Telescope Control Software in the ESO VLT Environment

The VST telescope control software in the ESO VLT environment

The VST telescope control software in the ESO VLT environment

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