C. Molfese

Active optics primary mirror support system for the 2.6 m VST telescope.

The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The 2.6 m primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.

The VST active primary mirror support system

The 2.6-m primary mirror of the VST telescope is equipped with an active optics system in order to correct low-order aberrations, constantly monitoring the optical quality of the image and controlling the relative position and the shape of the optical elements. Periodically an image analyser calculates the deviation of the image from the best quality. VST is equipped with both a Shack-Hartmann in the probe system and a curvature sensor embedded in the OmegaCAM instrument. The telescope control software decomposes the deviation into single optical contributions and calculates the force correction that each active element has to perform to achieve the optimal quality. The set of correction forces, one for each axial actuator, is computed by the telescope central computer and transmitted to the local control unit of the primary mirror system for execution. The most important element of the VST active optics is the primary mirror, with its active support system located within the primary mirror cell structure. The primary mirror support system is composed by an axial and a lateral independent systems and includes an earthquake safety system. The system is described and the results of the qualification test campaign are discussed.

VST telescope primary mirror active optics actuators firmware implementation

The VST (VLT Survey Telescope) is a 2.6 m class Alt-Az telescope in installation phase at Cerro Paranal in Northern Chile, at the European Southern Observatory (ESO) site. The VST is a wide-field imaging telescope dedicated to supply databases for the ESO Very Large Telescope (VLT) science and to carry out stand-alone observations in the Ultraviolet to Infrared spectral range. The VST is provided with an active optics control system to actively compensate the optical aberrations; it is based on 84 actuators controlling the shape of the primary mirror and a hexapode for secondary mirror positioning. The present paper focuses on the implementation of the microcontroller programming firmware for the Primary Mirror Actuators Electronic Control Board. The most relevant problems encountered during the implementation of this real time multitasking distributed control application are described; optimization problems due to low performing hardware platform, not provided with operating system, are also reported. Several described topics are applicable to other distributed control systems, requiring closed loop control system and communication capability with a higher level computer.

VST telescope azimuth and altitude axes control hardware

In a modern telescope the Azimuth (AZ) and Altitude (ALT) Axes have to perform a very accurate pointing and tracking. The tracking of celestial objects is a critical operation, during which the telescope axes have to compensate the earth rotation, allowing a stable image integration on the scientific instrument CCD. To accomplish this goal, the two axes control system is provided with state of the art encoders and tachometers, for position and speed feedback, together with motors controlled in torque preload, to avoid backlash effect. The closed loop control system is based on an axes Local Control Unit (LCU), based on VME Computer. In this paper the AZ and ALT Axes Control System of the VST (VLT Survey Telescope) is described. The VST is a 2.6 m class Alt-Azimuthal Survey Telescope in installation phase at Cerro Paranal in Northern Chile, at the European Southern Observatory (ESO) observation site. The VST Telescope was designed and implemented by I.N.A.F., Osservatorio Astronomico di Capodimonte. Nowadays the AZ and ALT axes mechanics and the related control system have already been accepted by ESO, shipped to Chile and integrated in Paranal.

Mechatronic distributed control system for telescope primary mirror active optics

The last generation optical telescopes use the active optics technology to actively compensate the errors of the optical system due to mirrors imperfections, thermal and gravity reasons; e.g. when the altitude angle changes the mirror shape slightly modifies depending on its aspect ratio (thinner mirrors have lower deformations) and on the mirror supporting system. The primary mirror shape is controlled by 84 force actuators disposed along concentric rings. The number of actuators along both radial and azimuthal directions depends on the maximum symmetry and order of the optical aberrations to be corrected. A distributed control system well suites to the problem of the primary mirror actuators control. The present paper is mainly focused on the control electronics and is referred to the experience related to the VLT Survey Telescope (VST), a telescope with a 2.6 m. primary mirror designed and developed by I.N.A.F., Osservatorio Astronomico di Capodimonte (OAC) in cooperation with the European Southern Observatory (ESO).

Survey Telescope control electronics

A last generation Survey Telescope requires a large amount of electromechanical actuators and sensors, completed with control electronics to make functioning not only the main axes to point and track the observed object, but a lot of subsystems as well, such as the Active Optics, the Probe, the Atmospheric Dispersion Corrector and the Hydraulic Bearings System. Each of them is based on different kinds of motors and transducers and related electronics, fulfilling the different subsystems requirements. Here the VST (VLT Survey Telescope) case is reported, giving a general overview of the main control electronics. The VST is a 2.6 m class Alt-Azimuthal Survey Telescope to be installed at Cerro Paranal in Northern Chile, at the European Southern Observatory (ESO) premises, one of the best observation sites worldwide. The VST Telescope was designed and realized by the I.N.A.F., Osservatorio Astronomico di Capodimonte. Nowadays its main structure has been already shipped to Chile, together with the Altitude and Azimuth axes control systems, meanwhile the subsystems controlling the two mirrors are still under completion in Naples.

VST primary mirror active optics electronics

The VLT Survey Telescope (VST), a telescope with a 2.6 m. primary mirror designed and implemented by I.N.A.F. in cooperation with the European Southern Observatory (ESO), is provided with an active optics system to correct the optical aberrations due to polishing imperfections, misalignments, thermal and gravity reasons. For the primary mirror, a distributed control system is required to impose the desired force values in a sufficient number of points to maintain the optimal shape in different positions of the altitude axis. The forces are applied by means of 84 electro-mechanical actuators, provided with an electronic Primary Mirror Actuator Control Boards (M1ACB). This paper focuses mainly on the hardware electronics and is referred to the control system new version, designed in 2007, whose implementation is in progress. The new design has taken into account all the experience done on the system previous version, solving all the encountered problems of functionality and reliability.

The VST telescope optomechatronic control system

The VST (VLT Survey Telescope) is a 2.6m optical ground-based telescope to be installed in the Cerro Paranal (Chile) observational station of the European Southern Observatory (ESO). It is a joint project of INAF-Osservatorio Astronomico di Capodimonte, responsible of the telescope design and realization, and ESO, responsible for the civil infrastructures and the daily operation of the instrument. The control system of the telescope is by definition an opto-mechatronic system. It combines mechatronic and optical disciplines together with the final aim to produce sharp images of star objects. Feedback control systems are partially based on mechatronic conventional sensors like position transducers, but also optical feedbacks coming from two separate technical CCD sensors are used to implement outer control loops for the compensation of optical aberrations e.g. introduced by the gravity, by shape imperfections or flexures in the mirrors, by thermal effects, by a not perfect alignment of the telescope axes.

The ExoMars DREAMS scientific data archive

DREAMS (Dust Characterisation, Risk Assessment, and Environment Analyser on the Martian Surface) is a payload accommodated on the Schiaparelli Entry and Descent Module (EDM) of ExoMars 2016, the ESA – Roscosmos mission to Mars successfully launched on 14 March 2016. The DREAMS data will be archived and distributed to the scientific community through the ESA’s Planetary Science Archive (PSA). All data shall be compliant with NASA’s Planetary Data System (PDS4) standards for formatting and labelling files. This paper summarizes the format and content of the DREAMS data products and associated metadata. The pipeline to convert the raw telemetries to the final products for the archive is sketched as well.

Active optics system of the VLT Survey Telescope.

This paper describes the active optics system of the VLT Survey Telescope, the 2.6-m survey telescope designed for visible wavelengths of the European Southern Observatory at Cerro Paranal, in the Atacama desert. The telescope is characterized by a wide field of view (1.42 deg diameter), leading to tighter active optics than in conventional telescopes, in particular for the alignment requirements. We discuss the effects of typical error sources on the image quality and present the specific solutions adopted for wavefront sensing and correction of the aberrations, which are based on the shaping of a monolithic primary mirror and the positioning of the secondary in five degrees of freedom.