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The present paper reports on the results of the validation test campaign of the ELT M1 Position Actuators (M1 PACTs). The main function of these actuators is positioning the 798 segments composing the primary mirror (M1) of the ELT with nanometric tracking error over the relatively large stroke of ten millimetres. In order to achieve this challenging goal the PACTs feature an hybrid actuation concept including a spindle drive for large and coarse movements in series with a piezo actuator for fine position adjustments. Active damping techniques are used to ensure robustness and benign dynamic response to perturbations transmitted through the supporting back structure. The design and manufacturing project of the M1 PACTs has recently entered in the final design phase. In this phase extensive validation testing is planned to verify that the final product is fit for purpose throughout its lifecycle. To this end the M1 PACT is first tested in stand-alone mode, with the objective of verifying its performances in a controlled and stable environment and deriving a reliable model of its dynamic response to be exploited for M1 performance estimation. Then several M1 PACTs are integrated in the M1 Test Stand, a small-scale mock-up of the primary mirror of the ELT. In this configuration multiple actuators are driven together to demonstrate relative position control between two segments. On the basis of the obtained results the paper discusses the expected M1 performance and possible control tuning strategies to be used during the commissioning of the ELT in Chile.

MAORY is a post-focal adaptive optics module that forms part of the first light instrument suite for the ELT. The main function of MAORY is to relay the light beam from the ELT focal plane to the client instrument while compensating the effects of the atmospheric turbulence and other disturbances affecting the wavefront from the scientific sources of interest.

The present work provides analysis of the ELT M4 control system interaction with the deformable mirror supporting structure. The aim is the verification of the system robustness in terms of both stability and performance. The results of the analysis suggested the opportunity to improve the system dynamic behavior through the addition of damping on the system supporting structure. The solution adopted has been the introduction of active damping using six proof mass actuators (PMAs) placed on the ELT M4 reference body (RB). The effectiveness of this solution, which is now part of the ELT M4 final design, is proved through numerical simulations. Moreover, the PMA design together with some experimental tests performed on a pre-series device will be presented.

Following the arrival of MATISSE, the second-generation of VLTI instrumentation is now complete and was simultaneously enhanced by a major facility upgrade including the NAOMI Adaptive Optics on the Auxiliary Telescopes. On the Unit Telescopes, significant efforts were also made to improve the injection stability into VLTI instruments. On top of GRAVITY's own evolution, its fringe tracker is now being used to allow coherent integrations on MATISSE (the so-called GRA4MAT project). Meanwhile, operations also evolved to be more flexible and make the most of an extended observing parameter space. In this context, we present an overview of the current VLTI performances. Finally, we will report on on-going improvements such as the extension of the longest baselines.

Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the new Earths in the $\alpha$ Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to $0.015 \lambda/D$ rms over 4h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations., Comment: Published in JATIS. This version is the manuscript resubmitted before acceptance, 30 pages, 14 figures

The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the instruments, and enable robust fringe tracking even in degraded conditions. We deployed a new adaptive optics module for interferometry (NAOMI) on the Auxiliary Telescopes. We present its design, performance, and effect on the observations that are carried out with the interferometric instruments., Comment: 10 pages, 18 figures, 2 tables, A&A forthcoming

The long commissioning of the Adaptive Optics Facility (AOF) project has been completed shortly after this conference, providing AO correction to two Very Large Telescope (VLT) foci supported by an adaptive secondary mirror and four laser guide stars. Four AO modes are delivered: a Single Conjugate AO (SCAO) system for commissioning purpose, wide field and medium field Ground Layer AO (GLAO) for seeing improvement and narrow field Laser Tomography AO (LTAO) for ultimate performance. This paper intends to describe the implemented AO baseline and to highlight the most relevant results and lessons learned. In particular, it will address the control and reconstruction strategy, the wavefront sensing baseline and the online telemetry used to optimize the system online, estimate the turbulence profile and calibrate the misregistrations. Focusing on the LTAO mode, we will describe the tomography optimization, by exploring the reconstruction parameter space. Finally, on sky performance results will be presented both in terms of strehl ratio and limiting magnitude.

The construction of a diffraction limitable telescope as large as the ESO’s ELT is enabled by its embedded deformable quaternary mirror. Besides its essential function in the telescope control, M4 also contributes to compensating the free atmosphere aberrations for all post-focal AO applications. The paper presents how the telescope manages M4 to maintain its optical performance while offering to the instruments a clean wavefront interface, supporting the desired AO functionalities. The paper reviews the telescope strategy to derive its wavefront dynamic properties directly from the analysis of the control data collected in science mode, with the goal to minimize the observatory time spent on dedicated wavefront calibration tasks.

The near-infrared GRAVITY instrument has become a fully operational spectro-imager, while expanding its capability to support astrometry of the key Galactic Centre science. The mid-infrared MATISSE instrument has just arrived on Paranal and is starting its commissioning phase. NAOMI, the new adaptive optics for the Auxiliary Telescopes, is about to leave Europe for an installation in the fall of 2018. Meanwhile, the interferometer infrastructure has continuously improved in performance, in term of transmission and vibrations, when used with both the Unit Telescopes and Auxiliary Telescopes. These are the highlights of the last two years of the VLTI 2nd generation upgrade started in 2015.

The ELT is a project led by the European Southern Observatory (ESO) for a 40-m class optical, near- and mid-infrared, ground-based telescope. When it will enter into operation, the ESO ELT will be the largest and most powerful optical telescope ever built. It will not only offer unrivalled light collecting power, but also exceedingly sharp images, thanks to its ability to compensate for the adverse effect of atmospheric turbulence on image sharpness. The basic optical solution for the ESO ELT is a folded three-mirror anastigmat, using a 39-m segmented primary mirror (M1), a 4-m convex secondary mirror (M2), and a 4-m concave tertiary mirror (M3), all active. Folding is provided by two additional flat mirrors sending the beams to either Nasmyth foci along the elevation axis of the telescope. The folding arrangement (flat M4 and M5 mirrors) is conceived to provide conveniently located flat surfaces for an adaptive shell (M4) and field stabilization (M5). This paper provides an update of the specifications, design, and manufacturing of the ESO ELT optical systems

In the last years the ELT Program has entered construction phase. For the large 39 meter segmented primary mirror unit with thousands of components this means that the start of the series production is getting closer, where the final hardware will be built. The M1 Unit has been broken down in products and a procurement strategy has been developed. Most of the major design decisions have been frozen and component specifications have been settled. Most of the suppliers have already been selected and contracts have been kicked off. This paper describes the ELT M1 Unit product breakdown and the procurement baseline for each product and its status. The production contracts would not have been possible without intense prototyping and verification strategies independent of the component contracts. Therefore, the paper also takes a look back at the prototypes and de-risking strategies, which had been put in place to prepare for construction phase. Ramping up the construction contracts involves finishing design details for some products while setting up production lines for others. This requires controlling interfaces and cross-contract dependencies, a challenge described in this paper. For continuous de-risking similar verification strategies than during the design phase are planned in parallel with the production until telescope assembly, integration and verification. These measures will increase confidence in the design choices, allow early discovery of remaining design flaws and provide training means for assembly and integration long time before all components of the ELT M1 are complete and being installed on Cerro Armazones in Chile. The paper will also give an outlook on these running and planned activities.

The MACAO curvature wavefront sensors have been designed as a generic adaptive optics sensor for the Very Large Telescope. Six systems have been manufactured and implemented on sky: four installed in the UTs Coude train as an AO facility for the VLTI, and two in UT’s instruments, SINFONI and CRIRES. The MACAO-VLTI have now been in use for scientific operation for more than a decade and are planned to be operated for at least ten more years. As second generation instruments for the VLTI were planned to start implementation in end of 2015, accompanied with a major upgrade of the VLTI infrastructure, we saw it as a good time for a rejuvenation project of these systems, correcting the obsolete components. This obsolescence correction also gave us the opportunity to implement improved capabilities: the correction frequency was pushed from 420 Hz to 1050 Hz, and an automatic vibrations compensation algorithm was added. The implementation on the first MACAO was done in October 2014 and the first phase of obsolescence correction was completed in all four MACAO-VLTI systems in October 2015 with the systems delivered back to operation. The resuming of the scientific operation of the VLTI on the UTs in November 2015 allowed to gather statistics in order to evaluate the improvement of the performances through this upgrade. A second phase of obsolescence correction has now been started, together with a global reflection on possible further improvements to secure observations with the VLTI.

The E-ELT M4 adaptive unit is a fundamental part of the E-ELT: it provides the facility level adaptive optics correction that compensates the wavefront distortion induced by atmospheric turbulence and partially corrects the structural deformations caused by wind. The unit is based on the contactless, voice-coil technology already successfully deployed on several large adaptive mirrors, like the LBT, Magellan and VLT adaptive secondary mirrors. It features a 2.4m diameter flat mirror, controlled by 5316 actuators and divided in six segments. The reference structure is monolithic and the cophasing between the segments is guaranteed by the contactless embedded metrology. The mirror correction commands are usually transferred as modal amplitudes, that are checked by the M4 controller through a smart real-time algorithm that is capable to handle saturation effects. A large hexapod provides the fine positioning of the unit, while a rotational mechanism allows switching between the two Nasmyth foci. The unit has entered the final design and construction phase in July 2015, after an advanced preliminary design. The final design review is planned for fall 2017; thereafter, the unit will enter the construction and test phase. Acceptance in Europe after full optical calibration is planned for 2022, while the delivery to Cerro Armazones will occur in 2023. Even if the fundamental concept has remained unchanged with respect to the other contactless large deformable mirrors, the specific requirements of the E-ELT unit posed new design challenges that required very peculiar solutions. Therefore, a significant part of the design phase has been focused on the validation of the new aspects, based on analysis, numerical simulations and experimental tests. Several experimental tests have been executed on the Demonstration Prototype, which is the 222 actuators prototype developed in the frame of the advanced preliminary design. We present the main project phases, the current design status and the most relevant results achieved by the validation tests.

International audience; GRAVITY is a near-infrared interferometric instrument that allows astronomers to combine the light of the four unit or four auxiliary telescopes of the ESO Very Large Telescope in Paranal, Chile. GRAVITY will deliver extremely precise relative astrometry and spatially resolved spectra. In order to study objects in regions of high extinction (e.g. the Galactic Center, or star forming regions), GRAVITY will use infrared wavefront sensors. The suite of four wavefront sensors located in the Coudé room of each of the unit telescopes are known as the Coudé Integrated Adaptive Optics (CIAO). The CIAO wavefront sensors are being constructed by the Max Planck Institute for Astronomy (MPIA) and are being installed and commissioned at Paranal between February and September of 2016. This presentation will focus on system tests performed in the MPIA adaptive optics laboratory in Heidelberg, Germany in preparation for shipment to Paranal, as well as on-sky data from the commissioning of the first instrument. We will discuss the CIAO instruments, control strategy, optimizations, and performance at the telescope.

In this paper, we investigate the problem of synthesizing performance weights and a controller that maximize the level of robust performance for a plant subject to both complex and real uncertainties. In particular, in this work the formulation proposed in Lanzon (2005a) and Lanzon and Cantoni (2003) is manipulated in order to include the possibility to handle both real and complex uncertainties. Additionally, we introduce a novel solution algorithm that presents performance and computational advantages with respect to those described in Lanzon (2005a) and Lanzon and Cantoni (2003).

In this paper we investigate the problem of synthesizing a controller that maximizes the level of robust performance for a plant subject to both complex and real uncertainties. The technique here developed uses the mixed-µ synthesis approach but, unlike the classical D,G-K iteration, it maximizes the size of the performance weights that in the H ∞ framework capture desired closed loop performance. This optimization is restricted by the constraint that there exists an internally stabilizing controller that achieves robust performance with respect to the maximized weights. Thus, performance weights and a controller that achieves an optimized level of robust performance are synthesized together in a systematic way. The designer is only required to specify the plant uncertain set and some frequency dependent functions, dubbed optimization directionalities, that reflect, in a qualitative way, the desired performance requirements. It is pointed out that choosing this directionality function is much easier than choosing the performance weights directly so that the design of good performance weights is greatly simplified.

We present a satellite path-planning technique able to make a set of identical spacecraft acquire a given configuration. The technique exploits a behavior-based approach to achieve an autonomous and distributed control over the relative geometry, making use of limited sensorial information. A desired velocity is defined for each satellite as a sum of different contributions coming from generic high-level behaviors. The behaviors are further defined by an inverse-dynamic calculation dubbed equilibrium shaping. We show that by considering only three different kinds of behavior it is possible to acquire a number of interesting formations, and we describe the theoretical framework needed to find the entire set. We find that by allowing a limited amount of communication the technique may be used also to form complex lattice structures. Several control feedbacks able to track the desired velocities are introduced and discussed. Our results suggest that sliding-mode control is particularly appropriate in connection with the developed technique.

In this paper, modern subspace identification methods are applied to a Multi-conjugate Adaptive optics Demonstrator, MAD, developed at ESO. The identified multi-input multi-output systems mapping voltages into slopes can be obtained on data taken in open/closed loop on beacon and in both SCAO and GLAO configurations. The advantages of the proposed approach is twofold: on the one hand the experiment to collect the data takes only few minutes during day time, it can be done on beacon, and all the computational effort is moved off-line. On the other hand, subspace identification provides the mathematical model necessary to design modern model-based controllers (e.g. linear quadratic control).

The E-ELT is an active and adaptive 39-m telescope, with an anastigmat optical solution (5 mirrors including two flats), currently being developed by the European Southern Observatory (ESO). The convex 4-metre-class secondary mirror (M2) is a thin Zerodur meniscus passively supported by an 18 point axial whiffletree. A warping harness system allows to correct low order deformations of the M2 Mirror. Laterally the mirror is supported on 12 points along the periphery by pneumatic jacks. Due to its high optical sensitivity and the telescope gravity deflections, the M2 unit needs to allow repositioning the mirror during observation. Considering its exposed position 30m above the primary, the M2 unit has to provide good wind rejection. The M2 concept is described and major performance characteristics are presented.

Most of the real-time control systems at the existing ESO telescopes were developed with "traditional" methods, using general purpose VMEbus electronics, and running applications that were coded by hand, mostly using the C programming language under VxWorks. As we are moving towards more modern design methods, we have explored a model-based design approach for real-time applications in the telescope area, and used the control algorithm of a standard telescope main axis as a first example. We wanted to have a clear work-flow that follows the "correct-by-construction" paradigm, where the implementation is testable in simulation on the development host, and where the testing time spent by debugging on target is minimized. It should respect the domains of control, electronics, and software engineers in the choice of tools. It should be a targetindependent approach so that the result could be deployed on various platforms. We have selected the Mathworks tools Simulink, Stateflow, and Embedded Coder for design and implementation, and LabVIEW with NI hardware for hardware-in-the-loop testing, all of which are widely used in industry. We describe how these tools have been used in order to model, simulate, and test the application. We also evaluate the benefits of this approach compared to the traditional method with respect to testing effort and maintainability. For a specific axis controller application we have successfully integrated the result into the legacy platform of the existing VLT software, as well as demonstrated how to use the same design for a new development with a completely different environment.

GALACSI is one of the Adaptive Optics (AO) systems part of the ESO Adaptive Optics Facility (AOF). It will use the VLT 4-Laser Guide Stars system, high speed and low noise WaveFront Sensor cameras (

We present in this paper an analysis of several tip-tilt on-sky data registered on adaptive optics systems installed on different telescopes (Gemini South, William Herschel Telescope, Large Binocular Telescope, Very Large Telescope, Subaru). Vibration peaks can be detected, and it is shown that their presence and location may vary, and that their origin is not always easy to determine. Mechanical solution that have been realized to mitigate vibrations are presented. Nevertheless, residual vibrations may still affect the instruments' performance, ranging from narrow high frequency vibration peaks to wide low frequency windshake-type perturbations. Power Spectral Densities (PSDs) of on-sky data are presented to evidence these features. When possible, indications are given regarding the gain in performance that could be achieved with adequate controllers accounting for vibration mitigation. Two examples of controller identification and design illustrate their ability to compensate for various types of disturbances (turbulence, windshake, vibration peaks, ...), showing a significant gain in performance. © 2012 SPIE., Adaptive Optics Systems III, July 1-6, 2012, Amsterdam, the Netherlands, Series: Proceedings of SPIE; no. 8447

In modern adaptive optics systems, lightly damped sinusoidal oscillations resulting from telescope structural vibrations have a significant deleterious impact on the quality of the image collected at the detector plane. Such oscillations are often at frequencies beyond the bandwidth of the wave-front controller that therefore is either incapable of rejecting them or might even amplify their detrimental impact on the overall AO performance. A technique for the rejection of periodic disturbances acting at the output of unknown plants, which has been recently presented in literature, has been adapted to the problem of rejecting vibrations in AO loops. The proposed methodology aims at estimating phase and amplitude of the harmonic disturbance together with the response of the unknown plant at the frequency of vibration. On the basis of such estimates, a control signal is generated to cancel out the periodic perturbation. Additionally, the algorithm can be easily extended to cope with unexpected time variations of the vibrations frequency by adding a frequency tracking module based either on a simple PLL architecture or on a classical extended Kalman filter. Oversampling can be also easily introduced to efficiently correct for vibrations approaching the sampling frequency. The approach presented in this contribution is compared against a different algorithm for vibration rejection available in literature, in order to identify drawbacks and advantages. Finally, the performance of the proposed vibration cancellation technique has been tested in realistic scenarios defined exploiting tip/tilt measurements from MACAO and NACO © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

In this paper two case studies, highlighting the role of the integrated modeling in the performance prediction and requirement verification of the E-ELT are presented. First example discusses the effect of the local wind load on the secondary mirror and the global wavefront error. Analysis and simulations showed that such local effect is one of the main contributors to the telescope error budget. A detailed modeling and simulation approach with the possibility to modify some important mechanical and control parameters led to a better understanding of the problem and searching for appropriate mitigation strategies. In the second example the effect of friction devices of the lateral support of the azimuth structure is presented. Such devices were originally proposed by the telescope structure contractor to reduce the induced stresses and force due to the temperature variations. A detailed modeling of the friction devices and its inclusion into the telescope dynamical model revealed that some performance and interface requirements are violated.

This paper compares several algorithms for target maneuver detection. The algorithms are based on input estimation coupled with Kalman filter or IMM filtering. The performance of each method is analyzed computing a Pareto frontier, which is based on different quality criteria such as root mean square (rms) of state estimation error and time of maneuver detection. It is shown that computation of such Pareto frontiers allows to compare the performance of the different detectors in a systematic way.

In this paper the problem of designing a robust controller with given structure for a plant describing a drag-free satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set representative of many drag-free missions with nonspherical test masses. The design plant is uncertain and a performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The v-gap metric is first used to derive a simplified uncertain design plant. Then the main performance requirement is broken down into requirements on the uncertain closed loop behavior of the simplified system. The fulfillment of this new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input–singleoutput controllers are designed that robustly achieve the desired level of performance. The method proposed allows one to properly account for the uncertainties in the system retaining the decentralized structure of the controller suggested by the peculiar features of the design plant.

In this paper the problem of designing a decentralized robust controller for a plant describing a drag-free satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set representative of many drag-free missions with non spherical test masses. A performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The main performance requirement is first broken down into requirements on the uncertain closed loop behavior of the system. The fulfillment of this new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input-single-output controllers are designed that robustly achieve the desired level of performance. The method proposed allows to properly account for the uncertainties in the design plant retaining the decentralized structure of the controller suggested by the peculiar features of the design plant.

The upgrade of the VLTI infrastructure for the 2nd generation instruments is now complete with the transformation of the laboratory, and installation of star separators on both the 1.8-m Auxiliary Telescopes (ATs) and the 8-m Unit Telescopes (UTs). The Gravity fringe tracker has had a full semester of commissioning on the ATs, and a first look at the UTs. The CIAO infrared wavefront sensor is about to demonstrate its performance relative to the visible wavefront sensor MACAO. First astrometric measurements on the ATs and astrometric qualification of the UTs are on-going. Now is a good time to revisit the performance roadmap for VLTI that was initiated in 2014, which aimed at coherently driving the developments of the interferometer, and especially its performance, in support to the new generation of instruments: Gravity and MATISSE., 9 pages, 6 figures, 1 table, Proc. SPIE 2016

In this paper we consider the coupling between the flexibility of a spacecraft equipped with variable speed control moment Gyros and its attitude control system, in the framework of command shaping techniques. The analysis is performed on the set of equation of motion written in an explicit form describing a flexible platform and N wheels gimballed to it. The attitude control system is designed upon a Lyapunov based feedback relying upon a rigid body model. Whenever the structure is not stiff enough, flexibility degrades the performances of the controller that fails to track the desired history. We therefore study the possibility of altering the tracking signal fed to the controller trying to get rid of the relevant frequencies notch filtering them in order to reduce vibrations. The results obtained for a test case attitude acquisition maneuver are presented and the benefit deriving from the command shaping technique evaluated and discussed.