Next-generation infrared astronomical instrumentation for ground-based and space telescopes could be based on MOEMS programmable slit masks for multi-object spectroscopy (MOS). MOS is used extensively to investigate astronomical objects optimizing the Signal-to-Noise Ratio (SNR): high precision spectra are obtained and the problem of spectral confusion and background level occurring in slitless spectroscopy is cancelled. Fainter limiting fluxes are reached and the scientific return is maximized both in cosmology, in galaxies formation and evolution, in stellar physics and in solar system small bodies characterization. We are developing a 2048 x 1080 Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the 3.6m Telescopio Nazionale Galileo (TNG) and called BATMAN. A two-arm instrument has been designed for providing in parallel imaging and spectroscopic capabilities. BATMAN will be mounted on the folded Nasmyth platform of TNG. Thanks to its compact design, high throughput is expected. The two arms with F/4 on the DMD are mounted on a common bench, and an upper bench supports the detectors thanks to two independent hexapods. The stiffness of the instrument is guaranteed thanks to a box architecture linking both benches. The volume of BATMAN is 1.4x1.2x0.75 m3, with a total mass of 400kg. Mounting of all sub-systems has been done and integration of the individual arms is under way. BATMAN on the sky is of prime importance for characterizing the actual performance of this new family of MOS instruments, as well as investigating the new operational procedures on astronomical objects (combining MOS and IFU modes, different spatial and spectral resolutions in the same FOV, absolute (spectro-) photometry by combining imaging and spectroscopy in the same instrument, automatic detection of transients …). This instrument will be placed at TNG by beginning-2019.
PROBA3 is the first high precision formation flying (FF) mission under responsibility of the European Space Agency (ESA). It is a technology mission devoted to in-orbit demonstration of the FF techniques, with two satellites kept at an average inter-satellite distance of 144m. The guiding scientific rationale is to realize a diluted coronagraph with the telescope (ASPIICS) on one satellite and the external occulter on the other satellite to observe the inner Solar corona at high spatial and temporal resolution, down to 1.08R⊙. The two spacecraft will be orbiting in a high eccentricity geocentric trajectory with perigee at 600km and the apogee at 60000Km and with an orbital period of 19hrs. The FF acquisition and operations will last about 6 hrs around the apogee and different metrology systems will be used for realizing and controlling the FF. The alignment active most critical sub-system is the Shadow Positioning Sensors (SPS), a series of Si-PM (Silicon Photomultiplier) disposed around the ASPIICS telescope's entrance aperture and measuring the proper positioning of the penumbra generated by the occulter at the center of the coronagraph’s optical reference frame. The FF alignment measurement accuracies required to the SPS are: 500μm for lateral movements and 50mm for longitudinal movements. This paper gives an overview of the opto-mechanical and electronic design and of the software algorithm for the FF intersatellite positioning. The expected performance of the SPS metrology system are reported.
In this paper we will review the ESPRESSO guiding algorithm for the Front End subsystem. ESPRESSO, the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, will be installed on ESO’s Very Large Telescope (VLT). The Front End Unit (FEU) is the ESPRESSO subsystem which collects the light coming from the Coudè Trains of all the Four Telescope Units (UTs), provides Field and Pupil stabilization better than 0.05’’ via piezoelectric tip tilt devices and inject the beams into the Spectrograph fibers. The field and pupil stabilization is obtained through a re-imaging system that collects the halo of the light out of the Injection Fiber and the image of the telescope pupil. In particular, we will focus on the software design of the system starting from class diagram to actual implementation. A review of the theoretical mathematical background required to understand the final design is also reported. We will show the performance of the algorithm on the actual Front End by adoption of telescope simulator exploring various scientific requirements.
Traditional techniques usually rely on optical feedback to align optical elements over all the degrees of freedom needed. This strongly iterative process implies the use of bulky and/or flexible adjustable mountings. Another solution under study consists in the characterization of every optomechanical elements and the integration of the parts without any optical feedback. The characterization can be performed using different 3D Coordinate Measuring Machines (like Laser Tracker, Articulated Arms and Cartesian ones) and referencing different parts like the optomechanical mounts or the optical surfaces. The alignment of the system is done adjusting the six degrees of freedom of every element with metallic shims. Those calibrated elements are used to correct the interfaces position of the semikinematic system composed by 3 screws and 3 pins. In this paper, the integration and alignment of the ESPRESSO Front End Units (FEUs) will be used as pathfinder to test different alignment methods and evaluate their performances.
In this paper we present an efficient tool developed to perform opto-mechanical tolerance and sensitivity analysis both for the preliminary and final design phases of a spectrograph. With this tool it will be possible to evaluate the effect of mechanical perturbation of each single spectrograph optical element in terms of image stability, i.e. the motion of the echellogram on the spectrograph focal plane, and of image quality, i.e. the spot size of the different echellogram wavelengths. We present the MATLAB-Zemax script architecture of the tool. In addition we present the detailed results concerning its application to the sensitivity analysis of the ESPRESSO spectrograph (the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations which will be soon installed on ESO’s Very Large Telescope) in the framework of the incoming assembly, alignment and integration phases.
slicer, is necessary to differently fold each field to correctly illuminate the echelle and this is made by cylindrical prisms glued onto a silica window. We present the integrated robotic system conceived to reach the required tolerances in term of alignment and integration. It consists in a tip/tilt stage to select the wedge angle, a rotational stage to select the right clock angle, coupled to an x-y stage to position the elements on the window and a z axis to perform the gluing.
ESPRESSO, Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, is now under the assembly, integration and verification phase and will be installed beginning next year at Paranal Observatory on ESO's Very Large Telescopes. The Front End is the modular system in the Combined Coudé Laboratory receiving the light from the four VLT Units, providing the needed connection between the input signal, i.e., object light, sky light, and calibration light, to feed the spectrograph through optical fibers. The modular concept of the FE Units drove the system design and the alignment workflow. We will show the integration method of the single FE modules adopted to guarantee the necessary repeatability between the different Units. The performances of the system in terms of image quality and encircled energy in the observed point spread function are reported. Finally, the strategy followed in the Paranal Combined Coudè Laboratory to define the convergence point of the four UTs is described, along with the procedure used to align the ground plates, the main structure, and the mode selector.
We present the details of a paraxial parametric model of a high resolution spectrograph which can be used as a tool, characterized by good approximation and reliability, at a system engineering level. This model can be exploited to perform a preliminary evaluation of the different parameters as long as different possible architectures of high resolution spectrograph like the one under design for the E-ELT (for the moment called E-ELT HIRES in order to avoid wrong association with the HIRES spectrograph at Keck telescope). The detailed equations flow concerning the first order effects of all the spectrograph components is described; in addition a comparison with the data of a complete physical ESPRESSO spectrograph model is presented as a model proof.
In this paper, we present the preliminary design of a smart telescope, i.e. an optomechanical device whose structure is able to monitor external loads (gravity, wind, thermal gradients, displacements caused by earthquake) and actively adapt to them in order to correct misalignments. To obtain that, the final solution will foresee the use of smart materials, or rather integrated smart structures containing sensors (such as fibre optics), and actuators (shape memory alloys or piezoelectric). Starting from the optical design, where the primary mirror is supposed to be in the class of 60cm diameter, with this work we illustrate the mechanical design philosophy. The basic idea is to conceive of a "low-performance" telescope from the stability point of view, in order to emphasize the environmental loads contributions, show that it is possible to correct them a posteriori, and generalize the results for more optimized structures (Serrurier-like). Therefore, it is shown the finite element model of a first naked version of the telescope (without smart structures), useful to know the displacements caused by predictable loads. In this first design phase, the secondary mirror re-centering is taken into account as a study case: to achieve the goal, Macro Fibre Composite piezoelectric actuators have been selected.
KEYWORDS: Actuators, Shape memory alloys, Microsoft Foundation Class Library, Smart structures, Image quality, Image processing, Deformable mirrors, Astronomy, Signal processing, Finite element methods
The astronomical instrumentation needs high level of image quality and stability. The quality of images processed by an optical instrument can be referred to the size of the spot and/or the point spread function (p.s.f.), while the stability is related to the displacement of the spot centroid during the observations. The importance of new design procedures for astronomical instruments through the direct design of the materials taking into account their functionalities integrating different approaches (FEM + raytracing) is then enhanced by the new upcoming requirement.
Different functional materials can be joined together exploiting each peculiar property in order to realize
an integrated structure better known as Smart Structure. They are capable of sensing and reacting to their environment in a predictable and desired manner, through the integration of various elements, such as sensors, actuators, power sources, signal processors, and communications network.
The Paper describes possible application related to two main functional materials: piezoelectric materials and Shape Memory Alloys.
The design of astronomical instrument is growing in dimension and complexity following ELT class telescopes.
The availability of new structural material like composite ones is asking for more robust and reliable designing
numerical tools. This paper wants to show a new opto-mechanical optimization approach developed starting
from a previously developed integrated design framework. The Idea is to reduce number of iteration in a multi-
variable structural optimization taking advantage of the embedded sensitivity routines that are available both
in FEA software and in raytracing ones. This approach provide reduced iteration number mainly in case of high
number of structural variable parameters.
The opto-mechanical conceptual design for the Front-End unit and the calibration unit of the ESPRESSO Spectrograph is
described in this paper. The front end system exploits a modular concept. Each FEU receive the beam directly from the
relative Telescope Coudé Train and the calibration light from the calibration unit. On the other side the FEU feeds the
fibers that carry the light to the spectrograph, corresponding in number and size to the scientific observing modes
conceived for Espresso. The selection is made through a Toggling Unit. Purpose of the Front/End is to provide the
needed connection between the input signal, i.e. Object light, Sky light, Calibration light, and the given output fiber in
any of the foreseen observing modes.
This paper presents the Espresso Anamorphic pupil Slicer (APSU) implementation. For ESPRESSO that will be installed
on ESO’s Very Large Telescope (VLT). In this work we will present the design and trade off for the pupil slicing system
introduced in order to increase the resolving power, effectively decreasing slit width. It’s based onto simplified optical
component that introduce large anamorphism while keeping low aberrations by means of cylindrical optics. We describe
here the trade off between slicing through two adjacent squared doublets and two achromatic prisms. Preliminary
integration and procurement is also discussed here.
Next-generation infrared astronomical instrumentation for ground-based and space telescopes could be based on
MOEMS programmable slit masks for multi-object spectroscopy (MOS). This astronomical technique is used
extensively to investigate the formation and evolution of galaxies.
We are developing a 2048x1080 Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the
Galileo telescope and called BATMAN. A two-arm instrument has been designed for providing in parallel imaging and
spectroscopic capabilities. The field of view (FOV) is 6.8 arcmin x 3.6 arcmin with a plate scale of 0.2 arcsec per
micromirror. The wavelength range is in the visible and the spectral resolution is R=560 for 1 arcsec object (typical slit
size). The two arms will have 2k x 4k CCD detectors.
ROBIN, a BATMAN demonstrator, has been designed, realized and integrated. It permits to determine the instrument
integration procedure, including optics and mechanics integration, alignment procedure and optical quality. First images
and spectra have been obtained and measured: typical spot diameters are within 1.5 detector pixels, and spectra generated
by one micro-mirror slits are displayed with this optical quality over the whole visible wavelength range. Observation
strategies are studied and demonstrated for the scientific optimization strategy over the whole FOV.
BATMAN on the sky is of prime importance for characterizing the actual performance of this new family of MOS
instruments, as well as investigating the operational procedures on astronomical objects. This instrument will be placed
on the Telescopio Nazionale Galileo mid-2015.
KEYWORDS: Prisms, Clocks, Tolerancing, Silica, Optics manufacturing, Assembly tolerances, Prototyping, Manufacturing, Control systems, Chemical elements
The multiprism device is a crucial component of the Espresso Anamorphic pupil Slicer (APSU). At the end of the slicer,
is necessary to differently fold each field to correctly illuminate the echelle. The solution is made by gluing cylindrical
prisms with proper bending low angle onto a support double plate silica window. We present here the integrated robotic
system conceived to reach the required tolerances in term of alignment and Integration. It consist in a tip tilt stage to
select the folding angle, coupled to an x-y stage to position the elements and a z axis to perform the gluing.
Keywords: Extra-solar Planet Atmospheres, High Resolution Spectroscopy, Espresso, front End
We designed the interferometric test of a 300 mm flat mirror, based onto a spherical mirror and a dedicated CGH. The spherical beam of the interferometer is quasi collimated to the desired diameter by the spherical mirror, used slightly off-axis, and the CGH performs the residual wavefront correction. We performed tests on a 200 mm and 300 mm flat mirrors, and compared the results to the ones obtained by stitching, showing an accuracy well within the designed value. The possibility to calibrate the cavity by subtracting out the figure errors of the spherical mirror has also been evaluated.
ESPRESSO is the next generation ground based European exoplanets hunter. It will combine the efficiency of modern
echelle spectrograph with extreme radial-velocity and spectroscopic precision. It will be installed at Paranal's VLT in
order to achieve two magnitudes gain with respect to its predecessor HARPS, and the instrumental radial-velocity
precision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes
to fund, design and build ESPRESSO on behalf of and in collaboration with ESO, the European Southern Observatory.
The spectrograph will be installed at the Combined Coudé Laboratory (CCL) of the VLT, it will be linked to the four 8.2
meters Unit Telescopes through four optical "Coudé trains" and will be operated either with a single telescope or with up
to four UTs, enabling an additional 1.5 magnitude gain. Thanks to its characteristics and ability of combining
incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in many fields of astronomy. Our
main scientific objectives are, however, the search and characterization of rocky exoplanets in the habitable zone of
quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. The project is, for
most of its workpackages, in the procurement or development phases, and the CCL infrastructure is presently under
adaptation work. In this paper, we present the scientific objectives, the capabilities of ESPRESSO, the technical solutions
for the system and its subsystems. The project aspects of this facility are also described, from the consortium and
partnership structure to the planning phases and milestones.
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