This work presents the latest results of new technological concepts for large aperture, lightweight telescopes using thin deployable active mirrors. The study is originally addressed to a spaceborne DIAL (Differential Absorption Lidar) at 935.5 nm for the measurement of water vapour profile in atmosphere, as an output of an ESA contract (whose preliminary results were presented at ICSO 2006).
The high versatility of these concepts allows to exploit the presented technology for any project willing to consider large aperture, segmented lightweight telescopes. A possible scientific application is for Ultra High Energy Cosmic Rays detection through the fluorescence traces in atmosphere and diffused Cerenkov signals observation via a Schmidt-like spaceborne LEO telescope with large aperture, wide Field of View (FOV) and low f/#.
A technology demonstrator has been manufactured and tested in order to investigate two project critical areas identified during the preliminary design: the performances of the long-stroke actuators used to implement the mirror active control and the mirror survivability to launch. In particular, this breadboard demonstrates at first that the mirror actuators are able to control with the adequate accuracy the surface shape and to recover a deployment error with their long stroke; secondly, the mirror survivability has been demonstrated using an electrostatic locking between mirror and backplane able to withstand without failure a vibration test representative of the launch environment.
This work presents a new technological concept for large aperture, lightweight, telescopes using thin deployable active mirrors, currently under a feasibility study for spaceborne Lidars.
The study is mainly addressed to a DIAL (Differential Absorption Lidar) at 935.5 nm for the measurement of water vapour profile in atmosphere, to be part of a typical small ESA Earth Observation satellite to be launched with ROCKOT vehicle. A detailed telescope optical design will be presented, including the results of angular and spatial resolution, effective optical aperture and radiometric transmission, optical alignment tolerances, stray-light and baffling. Also the results of a complete thermo-mechanical model will be shown, discussing temporal and thermal stability, deployment technology and performances, overall mass budget, technological and operational risk and system complexity.
The increasing interest on space telescopes for scientific applications leads to implement the manufacturing technology of the most critical element, i.e. the primary mirror: being more suitable a large aperture, it must be lightweight and deployable. The presented topic was originally addressed to a spaceborne DIAL (Differential Absorption LIDAR) mission operating at 935.5 nm for the measurement of water vapour profile in atmosphere, whose results were presented at ICSO 2006 and 2008.
Aim of this paper is to present the latest developments on the main issues related to the fabrication of a breadboard, covering two project critical areas identified during the preliminary studies: the design and performances of the long-stroke actuators used to implement the mirror active control and the mirror survivability to launch via Electrostatic Locking (EL) between mirror and backplane. The described work is developed under the ESA/ESTEC contract No. 22321/09/NL/RA.
The lightweight mirror is structured as a central sector surrounded by petals, all of them actively controlled to reach the specified shape after initial deployment and then maintained within specs for the entire mission duration. The presented study concerns: a) testing the Carbon Fiber Reinforced Plastic (CFRP) backplane manufacturing and EL techniques, with production of suitable specimens; b) actuator design optimisation; c) design of the deployment mechanism including a high precision latch; d) the fabrication of thin mirrors mock-ups to validate the fabrication procedure for the large shells.
The current activity aims to the construction of an optical breadboard capable of demonstrating the achievement of all these coupled critical aspects: optical quality of the thin shell mirror surface, actuators performances and back-plane - EL subsystem functionality.
The aim of this work is to describe the latest results of new technological concepts for Large Aperture Telescopes Technology (LATT) using thin deployable lightweight active mirrors. This technology is developed under the European Space Agency (ESA) Technology Research Program and can be exploited in all the applications based on the use of primary mirrors of space telescopes with large aperture, segmented lightweight telescopes with wide Field of View (FOV) and low f/#, and LIDAR telescopes. The reference mission application is a potential future ESA mission, related to a space borne DIAL (Differential Absorption Lidar) instrument operating around 935.5 nm with the goal to measure water vapor profiles in atmosphere. An Optical BreadBoard (OBB) for LATT has been designed for investigating and testing two critical aspects of the technology:
1) control accuracy in the mirror surface shaping. 2) mirror survivability to launch.
The aim is to evaluate the effective performances of the long stroke smart-actuators used for the mirror control and to demonstrate the effectiveness and the reliability of the electrostatic locking (EL) system to restraint the thin shell on the mirror backup structure during launch. The paper presents a comprehensive vision of the breadboard focusing on how the requirements have driven the design of the whole system and of the various subsystems. The manufacturing process of the thin shell is also presented.
The concept of a low areal density primary mirror, actively controlled by actuators, has been investigated through a demonstration prototype. A spherical mirror (400 mm diameter, 2.7 Kg mass) has been manufactured and tested in laboratory and on the optical bench, to verify performance, controllability and optical quality. In the present paper we will describe the prototype and the test results.
The design of large segmented mirrors, actively controlled both in shape and in differential piston, is one of the challenges space optics is facing, driven by the needs of the astronomical community.
The LATT project is an ESA contract under TRP programme to demonstrate the scalability of the technology from ground-based adaptive mirrors to space active primary mirrors. A prototype spherical mirror based on a 40 cm diameter 1 mm thin glass shell with 19 contactless, voice-coil actuators and co-located position sensors have been manufactured and integrated into a final unit with an areal density lower than 20 kg/m2. Laboratory tests demonstrated the controllability with very low power budget and the survival of the fragile glass shell exposed to launch accelerations, thanks to an electrostatic locking mechanism; such achievements pushes the technology readiness level toward 5. With this prototype, the LATT project explored the feasibility of using an active and lightweight primary for space telescopes. The concept is attractive for large segmented telescopes, with surface active control to shape and co-phase them once in flight. In this paper we will describe the findings of the technological advances and the results of the environmental and optical tests.
The Large Aperture Telescope Technology (LATT) goes beyond the current paradigm of future space telescopes, based on a deformable mirror in the pupil relay. Through the LATT project we demonstrated the concept of a low-weight active primary mirror, whose working principle and control strategy benefit from two decades of advances in adaptive optics for ground-based telescopes. We developed a forty centimeter spherical mirror prototype, with an areal density lower than 17 kg/m2, controlled through contactless voice coil actuators with co-located capacitive position sensors. The prototype was subjected to thermo-vacuum, vibration and optical tests, to push its technical readiness toward level 5. In this paper we present the background and the outcomes of the LATT activities under ESA contract (TRP programme), exploring the concept of a lightweight active primary mirror for space telescopes. Active primaries will open the way to very large segmented apertures, actively shaped, which can be lightweight, deployable and accurately phased once in flight.
SHARK-NIR channel is one of the two coronagraphic instruments proposed for the Large Binocular Telescope, in the framework of the call for second generation instruments, issued in 2014. Together with the SHARK-VIS channel, it will offer a few observing modes (direct imaging, coronagraphic imaging and coronagraphic low resolution spectroscopy) covering a wide wavelength domain, going from 0.5μm to 1.7μm.
Initially proposed as an instrument covering also the K-band, the current design foresees a camera working from Y to H bands, exploiting in this way the synergy with other LBT instruments such as LBTI, which is actually covering wavelengths greater than L' band, and it will be soon upgraded to work also in K band. SHARK-NIR has been undergoing the conceptual design review at the end of 2015 and it has been approved to proceed to the final design phase, receiving the green light for successive construction and installation at LBT.
The current design is significantly more flexible than the previous one, having an additional intermediate pupil plane that will allow the usage of coronagraphic techniques very efficient in term of contrast and vicinity to the star, increasing the instrument coronagraphic performance. The latter is necessary to properly exploit the search of giant exo-planets, which is the main science case and the driver for the technical choices of SHARK-NIR. We also emphasize that the LBT AO SOUL upgrade will further improve the AO performance, making possible to extend the exo-planet search to target fainter than normally achieved by other 8-m class telescopes, and opening in this way to other very interesting scientific scenarios, such as the characterization of AGN and Quasars (normally too faint to be observed) and increasing considerably the sample of disks and jets to be studied.
Finally, we emphasize that SHARK-NIR will offer XAO direct imaging capability on a FoV of about 15"x15", and a simple coronagraphic spectroscopic mode offering spectral resolution ranging from few hundreds to few thousands. This article presents the current instrument design, together with the milestones for its installation at LBT.
This article presents a proposal aimed at investigating the technical feasibility and the scientific capabilities of high
contrast cameras to be implemented at LBT. Such an instrument will fully exploit the unique LBT capabilities in
Adaptive Optics (AO) as demonstrated by the First Light Adaptive Optics (FLAO) system, which is obtaining excellent
results in terms of performance and reliability. The aim of this proposal is to show the scientific interest of such a
project, together with a conceptual opto-mechanical study which shows its technical feasibility, taking advantage of the
already existing AO systems, which are delivering the highest Strehl experienced in nowadays existing telescopes.
Two channels are foreseen for SHARK, a near infrared channel (2.5-0.9 um) and a visible one (0.9 – 0.6 um), both
providing imaging and coronagraphic modes. The visible channel is equipped with a very fast and low noise detector
running at 1.0 kfps and an IFU spectroscopic port to provide low and medium resolution spectra of 1.5 x 1.5 arcsec
fields.
The search of extra solar giant planets is the main science case and the driver for the technical choices of SHARK, but
leaving room for several other interesting scientific topics, which will be briefly depicted here.
This paper describes an innovative approach for a new generation of large aperture, deployable telescopes for advanced
space LIDAR applications, using the thin active mirror technology. The overall telescope design is presented with a
special attention to the optical performances analysis. The mechanical layout with details of the deployment and baffling
technique is shown; the complete satellite thermo-elastic analysis mapping the primary mirror deformation due to the
thermal loads is presented; the control system architecture is explained and the optical design including the angular and
spatial resolution, effective optical aperture and radiometric transmission, optical alignment tolerances, straylight and
baffling is deeply discussed. Finally an overview of different mission profiles that this technology can satisfy is
presented; the imaging performances can be achieved using the shown technology tuning the surface control to higher
performances.
This paper describes the design, manufacturing and test of a ground demonstrator of an innovative technology able to
realize lightweight active controlled space-borne telescope mirror. This analysis is particularly devoted to applications
for a large aperture space telescope for advanced LIDAR, but it can be used for any lightweight mirror. For a space-borne
telescope the mirror weight is a fundamental parameter to be minimized (less than 15 Kg/m2), while maximizing
the optical performances (optical quality better than &lgr;/3). In order to guarantee these results, the best selected solution is
a thin glass primary mirror coupled to a stiff CFRP (Carbon Fiber Reinforced Plastic) panel with a surface active control
system. A preliminary design of this lightweight structure highlighted the critical areas that were deeply analyzed by the
ground demonstrator: the 1 mm thick mirror survivability on launch and the actuator functional performances with low
power consumption. To preserve the mirror glass the Electrostatic Locking technique was developed and is here
described. The active optics technique, already widely used for ground based telescopes, consists of a metrology system
(wave front sensor, WFS), a control algorithm and a system of actuators to slightly deform the primary mirror and/or
displace the secondary, in a closed-loop control system that applies the computed corrections to the mirror's optical
errors via actuators. These actuators types are properly designed and tested in order to guarantee satisfactory
performances in terms of stroke, force and power consumption. The realized and tested ground demonstrator is a square
CFRP structure with a flat mirror on the upper face and an active actuator beneath it. The test campaign demonstrated the
technology feasibility and robustness, supporting the next step toward the large and flat surface with several actuators.
AMBER is the focal near-infrared instrument of the VLTI combining
2 or 3 telescopes in the J, H and K bands with 3 spectral resolution modes. It uses single-mode fibers to ensure modal filtering and high measurement accuracies. AMBER has been integrated and tested in Grenoble during 2003. We report in this paper the lab performances of the instrument in terms of instrumental contrast, measurement accuracy and stability, and throughput.
AMBER, Astronomical Multi BEam combineR, is the near-infrared focal instrument dedicated to the VLTI. It is designed to combine three of the VLTI Telescopes and to work simultaneously in the J, H and K spectral bands (1.0 to 2.4 μm).
The project successfully passed the Preliminary Acceptance in Europe in November 2003, resulting in the validation of the instrument laboratory performance1, of the compliance with the initial scientific specifications, and of the acceptance of ESO for AMBER to be part of the VLTI. After the transportation of the instrument to Paranal, Chile in January 2004, the Assembly Integration and Verification phase occurred mid-March to succeed with the first fringes observing bright stars with the VLTI siderostats.
This paper describes the different steps of the AIV and the first results in terms of instrumental stability, estimated visibility and differential phase.
The instrumentation for VLT/VLTI 1 facility of the European Southern Observatory at Paranal (Chile)includes the infrared beam-combiner called AMBER, that covers the near infrared bands up to 2.5 μm. The cold spectrograph we describe is the AMBER subsystem responsible of wavelength analysis and several other functions, all of them performed by means of optics, analyzers, and mechanisms working at the temperature of liquid nitrogen boiling at atmospheric pressure. The cryo-mechanical design of the spectrograph we describe here
used extensively the methods of finite element analysis and the laboratory tests validated this approach. The final optical quality we measured in the laboratory before shipping the instrument to Grenoble or integration (December 2002),is well inside the specification the AMBER staff assigned to the spectrograph. Simulations show that its total contribution to visibility loss of AMBER is less than 2%.
AMBER is the General User near infrared focal instrument of the Very Large Telescope Interferometer. Its a single mode, dispersed fringes, three telescopes instrument. A limiting magnitude of the order of H=13 will allow to tackle a fair sample of extra galactic targets. A very high accuracy, in particular in color differential phase and closure phase modes gives good hope for very high dynamic range observation, possibly including hot extra solar planets. The relatively high maximum spectral resolution, up to 10000, will allow some stellar activity observations. Between this extreme goals, AMBER should have a wide range of applications including Young Stellar Objects, Evolved Stars, circumstellar material and many others. This paper tries to introduce AMBER to its future users with
information on what it measures, how it is calibrated and hopes
to give the readers ideas for applications.
AMBER is a focal instrument for the Very Large Telescope Interferometer working in the near infrared from 1.1 to 2.4 micrometers . It has been designed having in mind the General User of interferometric observations and the full range of his possible astrophysical programs. However the three programs used to define the key specifications have been the study of Young Stellar Objects, the study of Active Galactic Nuclei dust tori and broad line regions and the measure of masses and spectra of hot Extra Solar Planets. AMBER combines up to three beams produced by the VLTI 8 m Unit Telescopes equipped with Adaptive Optics and/or by the 1.8 m Auxiliary Telescopes. The fringes are dispersed with resolutions ranging from 35 to 10000. It is optimized for high accuracy single mode measurements of the absolute visibility, of the variation of the visibility and phase with wavelength (differential interferometry) and of phase closure relations with three telescopes. The instrument and its software are designed to allow a highly automated user friendly operation and an easy maintenance.
AMBER, Astronomical Multi BEam combineR, is the near- infrared instrument dedicated to the VLTI. It is presently designed to work with three of either the 8 m or the 1.8 m telescopes from 1 to 2.5 micrometers . Given the expected scientific performance and requirements for AMBER, we derived the functional analysis leading to the present optical configuration using optical fibers to spatially filter the wavefront perturbations, and dispersed fringes. The expected performance is presented in terms of optical quality and sensitivity to misalignments.
We describe the general characteristics of the TIRGO infrared telescope, located on Gornergrat (Switzerland), and its most recent instrumentation. This telescope is specifically designed for infrared astronomical observations. Two newly designed instruments are presented: the imaging camera Arnica and the long-slit spectrometer LonGSp, both based on two-dimensional array detectors.
The near infrared camera/spectrometer (or NICS, for brevity), that we are currently designing for first-light operations of the Italian Telescope Galileo (TNG), makes use of a set of optics for achieving both good quality imaging on equivalent fields of view on the sky as large as 4' X 4', and moderate resolution spectroscopy at a resolving power of 400 - 2200, with the possibility to reach 7500 in the future, over the near infrared bands from 0.95 micrometers up to 2.50 micrometers . We describe the details of the optical design, with the overall requests we imposed on the project in terms of performance and total size.
ARNICA (ARcetri Near Infrared CAmera) is the imaging camera for the near infrared bands between 1.0 and 2.5 micrometers that Arcetri Observatory has designed and built as a general facility for the TIRGO telescope (1.5 m diameter, f/20) located at Gornergrat (Switzerland). The scale is 1' per pixel, with sky coverage of more than 4' X 4' on the NICMOS 3 (256 X 256 pixels, 40 micrometers side) detector array. The optical path is compact enough to be enclosed in a 25.4 cm diameter dewar; the working temperature is 76 K. The camera is remotely controlled by a 486 PC, connected to the array control electronics via a fiber-optics link. A C-language package, running under MS-DOS on the 486 PC, acquires and stores the frames, and controls the timing of the array. We give an estimate of performance, in terms of sensitivity with an assigned observing time, along with some details on the main parameters of the NICMOS 3 detector.
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