References of "Stockman, Yvan"
     in
Bookmark and Share    
Full Text
See detailDevelopment of digital holography in the long wave infrared range for assessment of space reflectors
Thizy, Cédric ULg; Vandenrijt, Jean-François ULg; Georges, Marc ULg et al

in Proceedings of ICSO 2010 - International Conference on Space Optics (2010, October)

Detailed reference viewed: 49 (10 ULg)
Full Text
See detailThermo-elastic distortion measurements by holographic interferometry and correlation with finite element models for SiC connections/junctions on spacecraft
Thizy, Cédric ULg; Stockman, Yvan ULg; Eliot, Fabienne et al

Conference (2010, September)

Scientific, earth observation and telecommunication spacecrafts are submitted to severe thermal environments while their mission performance requires more and more high stable structures. Due to on-ground ... [more ▼]

Scientific, earth observation and telecommunication spacecrafts are submitted to severe thermal environments while their mission performance requires more and more high stable structures. Due to on-ground constraints, the verification by test of the performances of these stable structures is usually limited. However accurate prediction methodology and verification capability of thermal distortions becomes mandatory for ensuring the in-orbit performance objectives of future programs. The main thermo-elastic contributors of the final stability performances are: - Material and assembly physical properties knowledge (Coefficient of Thermal Expansion, Young modulus, Poisson ratio…) - Modeling and simulation capabilities: temperature mapping, accurate thermo-elastic finite element models… - Verification test performances: advanced measurement techniques are required to characterize and determine the different main contributors to the final end to end performance and to perform accurate correlation. In this study, material characteristics are assumed to be well known. The objective was to improve and develop analytical predictions and verification of thermo elastic distortions using sample testing for modeling correlation. The samples have been chosen to be representative of the connections/junctions that can be encountered in stable structures on spacecraft and can have a dominant impact on the instrument stability. The results presented in this paper concern SiC/SiC and SiC/TA6V bonded and bolted samples. For the tests, temperature variations between -20°C and +15°C from ambient have been applied to the samples. Thermo-elastic distortions have been measured with a holographic camera. This holographic camera can measure displacements in the range of 20 nm to 20 m without physical contact with the samples. The tests results have been compared to the predictions obtained by Finite Element Modelling. From this comparison modelling guidelines have been issued with the aim of improving the accuracy of computed thermo elastic distortions: the FEM predictions lead to quite good correlation with the test data, with most of the time less than 10% discrepancies. A second phase to this study is planned. The objective is to implement all the benefits on improvement of thermo-elastic distortions predictions and verification achieved during the first phase on real spacecraft hardware. [less ▲]

Detailed reference viewed: 106 (3 ULg)
Full Text
See detailFirst steps in the development of a piston sensor for large aperture space telescopes
Guerri, Géraldine ULg; Roose, Stéphane ULg; Stockman, Yvan ULg et al

in Oschmann, J.; Clampin, M.; MacEwen, H. (Eds.) Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave (2010, July 01)

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes ... [more ▼]

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes or large segmented telescopes. One of the major issues is the phasing of the sub-apertures or the segments of such telescopes. A cophasing sensor is therefore mandatory to achieve the ultimate resolution of these telescopes. In this framework, Liège Space Center (CSL) concern is the development of a compact cophasing sensor to phase new large lightweight segmented mirrors for future space telescopes. The sensor concept has its origins in new phase retrieval algorithms which have been recently developed. In this paper, we outline the concept and the experimental validation results of our piston sensor breadboard which is currently under development in our laboratory. Finally, future prospects and further developments of our experiment are presented. [less ▲]

Detailed reference viewed: 62 (18 ULg)
Full Text
See detailBaffles design of the PROBA-V wide FOV TMA
Mazzoli, Alexandra ULg; Holbrouck, Piet; Houbrechts, Yvette ULg et al

in Proceedings of ICSO 2010 - International Conference on Space Optics (Rhodes 2010, October) (2010)

Proba-V payload is a successor of the Vegetation instrument, a multispectral imager flown on Spot-4 and subsequently on Spot-5, French satellites for Earth Observation and defence. The instrument, with ... [more ▼]

Proba-V payload is a successor of the Vegetation instrument, a multispectral imager flown on Spot-4 and subsequently on Spot-5, French satellites for Earth Observation and defence. The instrument, with its wide field of view, is capable of covering a swath of 2200 km, which, in combination with a polar low Earth orbit, guarantees a daily revisit. The lifetime of Spot-5 expires in early 2013, and to ensure the continuity of vegetation data, BELSPO, the Belgian Federal Science Policy Office, supported the development of an instrument that could be flown on a Proba type satellite, a small satellite developed by the Belgian QinetiQ Space (previously known as Verhaert Space). The challenge of this development is to produce an instrument responding to the same user requirements as Vegetation, but with an overall mass of about 30 kg, while the Vegetation instrument mass is 130 kg. This development had become feasible thanks to a number of new technologies that have been developed since the nineties, when Vegetation was first conceived, namely Single Point Diamond Turning fabrication of aspherical mirrors and efficient VNIR and SWIR detectors. The Proba-V payload is based on three identical reflective telescopes using highly aspherical mirrors in a TMA (Three Mirrors Anastigmat) configuration. Each telescope covers a field of view of 34o to reach the required swath. One of the challenges in the development of the PROBA-V instrument is the efficient reduction of stray light. Due to the mass and volume constraints it was not possible to implement a design with an intermediate focus to reduce the stray light. The analysis and minimization of the in-field stray light is an important element of the design because of the large FOV and the surface roughness currently achievable with the Single Point Diamond Turning. This document presents the preliminary baffle layout designed for the Three Mirrors Anastigmatic (TMA) telescope developed for the Proba-V mission. This baffling is used to avoid 1st order stray light i.e. direct stray light or through reflections on the mirrors. The stray light from the SWIR folding mirror is also studied. After these preliminary analyses the mechanical structure of the TMA is designed then verified in term of vignetting and stray light. [less ▲]

Detailed reference viewed: 115 (2 ULg)
Full Text
Peer Reviewed
See detailPre-flight calibration of LYRA, the solar VUV radiometer on board PROBA2
Benmoussa, Ali; Dammasch, Ingolf; Hochedez, Jean-François et al

in Astronomy and Astrophysics (2009), 508(2), 1085-1094

Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy ... [more ▼]

Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft. Methods: The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard.<BR /> Results: A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1 and 11 was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance. [less ▲]

Detailed reference viewed: 157 (10 ULg)
Full Text
See detailAlignement et optimisation d'un simulateur solaire d'une configuration de 1SC à une configuration à 10SC.
De Rauw, Dominique ULg; Mazy, Emmanuel ULg; Stockman, Yvan ULg et al

Conference (2009, November 18)

Ce papier décrit les tâches réalisées dans le cadre d’un projet de modification du simulateur solaire de l’ESA afin de l’adapter et le faire passer d’une configuration où le flux est de une constante ... [more ▼]

Ce papier décrit les tâches réalisées dans le cadre d’un projet de modification du simulateur solaire de l’ESA afin de l’adapter et le faire passer d’une configuration où le flux est de une constante solaire vers une configuration à 10 constantes solaires. Nous exposons les tâches réalisées par le Centre Spatial de Liège en ce qui concerne la modélisation et la simulation des configurations ainsi que les éléments mis au point pour l’alignement des miroirs du simulateur solaire et pour la mesure d’uniformité de flux. [less ▲]

Detailed reference viewed: 48 (9 ULg)
See detailDynamic holographic interferometry for dilatation measurements in vacuum-thermal conditions
Thizy, Cédric ULg; Barbier, Christian ULg; Barzin, Pascal ULg et al

in Lehmann, Peter (Ed.) Proc. SPIE Vol 7398 on Optical Measurement Systems for Industrial Inspection VI (2009, June)

Detailed reference viewed: 48 (16 ULg)
Full Text
Peer Reviewed
See detailModular bimorph mirrors for adaptive optics
Rodrigues, Goncalo; Bastaits, Renaud; Roose, Stéphane ULg et al

in Optical Engineering : The Journal of the Society of Photo-Optical Instrumentation Engineers (2009), 3(48),

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror ... [more ▼]

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100to200mm ; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5mm , and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics. [less ▲]

Detailed reference viewed: 14 (0 ULg)
Full Text
Peer Reviewed
See detailOptical methods for non-contact measurements of membranes
Roose, Stéphane ULg; Stockman, Yvan ULg; Rochus, Pierre ULg et al

in Acta Astronautica (2009), 65(9-10), 1317-1329

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film ... [more ▼]

Structures for space applications very often suffer stringent mass constraints. Lightweight structures are developed for this purpose, through the use of deployable and/or inflatable beams, and thin-film membranes. Their inherent properties (low mass and small thickness) preclude the use of conventional measurement methods (accelerometers and displacement transducers for example) during on-ground testing. In this context, innovative non-contact measurement methods need to be investigated for these stretched membranes. The object of the present project is to review existing measurement systems capable of measuring characteristics of membrane space-structures such as: dot-projection videogrammetry (static measurements), stereo-correlation (dynamic and static measurements), fringe projection (wrinkles) and 3D laser scanning vibrometry (dynamic measurements). Therefore, minimum requirements were given for the study in order to have representative test articles covering a wide range of applications. We present test results obtained with the different methods on our test articles. [less ▲]

Detailed reference viewed: 63 (6 ULg)
Full Text
See detailPhase control strategies for stabilization of photorefractive holographic interferometer
Thizy, Cédric ULg; Georges, Marc ULg; Lemaire, Philippe ULg et al

in Slangen, P.; Cerruti, C. (Eds.) Speckle06 : Speckles, From Grains to Flowers (2006, September)

A current problem encountered in holographic interferometry systems is the phase variations that arise from vibrations, from the use of optical fiber in one arm, by air convection or by unwanted movement ... [more ▼]

A current problem encountered in holographic interferometry systems is the phase variations that arise from vibrations, from the use of optical fiber in one arm, by air convection or by unwanted movement between the object and the measurement device. The holographic device developed by CSL based on photorefractive BSO crystals has the advantage of high resolution fringes with the capability of self-processing and indefinite reusability. The weakness of the technique is a response time that is often slow compared to external perturbations. For applications outside the laboratory, we decided to find solutions adapted to the holographic camera and which tend to limit or to eliminate the effect of such phase variations. An error signal is measured from one or another technique which measure the phase variations and which counteracts on an active element in the interferometer to stabilize the phase during recording. Different solutions have been analysed and are presented here. Interferograms were obtained with and without implementation of the phase control system that show the interest of such approach. Some of the system presented are only adapted to photorefractive holographic interferometry, making use of some crystal diffraction properties. Other systems can be used with other kind of interferometers. [less ▲]

Detailed reference viewed: 21 (3 ULg)
Full Text
Peer Reviewed
See detailPerformance of diamond detectors for VUV applications
BenMoussa, A.; Theissen, A.; Scholze, F. et al

in Nuclear Instruments & Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment (2006), 568(1), 398-405

We report on experimental results with photodetectors made of diamond. the Large Yield Radiometer (LYRA), will use such detectors for the first time for a solar physics space instrument. A (LYRA) set of ... [more ▼]

We report on experimental results with photodetectors made of diamond. the Large Yield Radiometer (LYRA), will use such detectors for the first time for a solar physics space instrument. A (LYRA) set of measurement campaigns was carried out to obtain their XUV-to-VIS characterization (responsivity, linearity, stability, homogeneity). The responsivity has been measured from the XUV to the NIR, in the wavelength range 1-1127 nm (i.e. 1240-1.1 eV). The diamond detectors exhibit a photoresponse varying in the 40-75 mA/W range at 7 nm and demonstrate a visible rejection ratio (200 versus 500 nm) larger than four orders of magnitude. We show that diamond photodetectors are sensitive sensors for VUV photons, stable within a few percent, with a good linearity and moderate homogeneity. © 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 14 (2 ULg)
Full Text
Peer Reviewed
See detailLYRA, a solar UV radiometer on PROBA2
Hochedez; Schmutz, W.; Stockman, Yvan ULg et al

in Advances in Space Research (2006), 37

LYRA is the solar UV radiometer that will embark in 2006 onboard Proba2, a technologically oriented ESA micro-mission. LYRA is designed and manufactured by a Belgian–Swiss–German consortium (ROB, PMOD/WRC ... [more ▼]

LYRA is the solar UV radiometer that will embark in 2006 onboard Proba2, a technologically oriented ESA micro-mission. LYRA is designed and manufactured by a Belgian–Swiss–German consortium (ROB, PMOD/WRC, IMOMEC, CSL, MPS and BISA) with additional international collaborations. It will monitor the solar irradiance in four UV passbands. They have been chosen for their relevance to Solar Physics, Aeronomy and Space Weather: (1) the 115–125 nm Lyman-a channel, (2) the 200–220 nm Herzberg continuum range, (3) the Aluminium filter channel (17–70 nm) including He II at 30.4 nm and (4) the Zirconium filter channel (1–20 nm). The radiometric calibration will be traceable to synchrotron source standards (PTB and NIST). The stability will be monitored by onboard calibration sources (LEDs), which allow to distinguish between potential degradations of the detectors and filters. Additionally, a redundancy strategy maximizes the accuracy and the stability of the measurements. LYRA will benefit from wide bandgap detectors based on diamond: it will be the first space assessment of a pioneering UV detectors program. Diamond sensors make the instruments radiation-hard and solar-blind: their high bandgap energy makes them insensitive to visible light and, therefore, make dispensable visible light blocking filters, which seriously attenuate the desired ultraviolet signal. Their elimination augments the effective area and hence the signal-to-noise, therefore increasing the precision and the cadence. The SWAP EUV imaging telescope will operate next to LYRA on Proba2. Together, they will establish a high performance solar monitor for operational space weather nowcasting and research. LYRA demonstrates technologies important for future missions such as the ESA Solar Orbiter [less ▲]

Detailed reference viewed: 7 (0 ULg)
See detailDynamic holography for the space qualification of large reflectors
Thizy, Cédric ULg; Stockman, Yvan ULg; Doyle, D. et al

in Optical Fabrication, Testing, and Metrology II (2005, October)

The next generation of infrared - sub mm space telescopes requires reflectors with large dimensions, high quality and, according to weight issues, are based on composite or new materials technology. The ... [more ▼]

The next generation of infrared - sub mm space telescopes requires reflectors with large dimensions, high quality and, according to weight issues, are based on composite or new materials technology. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of these reflectors shape and antenna structures and to verify their performance under simulated space conditions (vacuum, low-high temperatures). A holographic camera for the verification and validation of this type of reflector in a space environment is presented. A diffuser is implemented to measure the deformations of reflective surfaces in a more flexible way. The system has been made compatible with the vacuum conditions. Some elements of the holographic camera (camera lenses, CCD, crystal, optical fibre) have been adapted and tested under vacuum. The metrological certification of the whole system is realised by the measurement of a parabolic CFRP reflector with a 1.1 meter diameter. The results are compared to the one achieved with a high spatial resolution IR interferometer on the same reflector in laboratory conditions and under thermal vacuum conditions. This later test consists in measuring the deformations of the reflector between an initial state at a selected temperature and a final state at another temperature. The comparison between the high spatial resolution IR interferometer and this dynamic holographic method showed very good qualitative and quantitative agreement between the techniques, thus verifying the potential of this new Holographic approach. [less ▲]

Detailed reference viewed: 72 (3 ULg)
Full Text
See detailCryo-optical testing of large aspheric reflectors operating in the sub mm range
Roose, Stéphane ULg; Houbrechts, Yvette ULg; Mazzoli, Alexandra ULg et al

in Zhang, Y.; Jiang, W.; Cho, M. (Eds.) Proceedings of the 2nd SPIE symposium on Advanced Optical Manufacturing and Testing Technologies (2005, August)

The cryo-optical testing of the PLANCK primary reflector (elliptical off-axis CFRP reflector of 1550 mm x 1890 mm) is one of the major issue in the payload development program. It is requested to measure ... [more ▼]

The cryo-optical testing of the PLANCK primary reflector (elliptical off-axis CFRP reflector of 1550 mm x 1890 mm) is one of the major issue in the payload development program. It is requested to measure the changes of the Surface Figure Error (SFE) with respect to the best ellipsoid, between 293 K and 50 K, with a 1 μm RMS accuracy. To achieve this, Infra Red interferometry has been used and a dedicated thermo mechanical set-up has been constructed. This paper summarises the test activities, the test methods and results on the PLANCK Primary Reflector - Flight Model (PRFM) achieved in FOCAL 6.5 at Centre Spatial de Liege (CSL). Here, the Wave Front Error (WFE) will be considered, the SFE can be derived from the WFE measurement. After a brief introduction, the first part deals with the general test description. The thermo-elastic deformations will be addressed: the surface deformation in the medium frequency range (spatial wavelength down to 60 mm) and core-cell dimpling. [less ▲]

Detailed reference viewed: 34 (3 ULg)
Full Text
Peer Reviewed
See detailQualification of large reflectors in space environment with a holographic camera based on a BSO crystal
Thizy, Cédric ULg; Stockman, Yvan ULg; Lemaire, Philippe ULg et al

in Zhang, G.; Kip, D.; Nolte, D. (Eds.) et al Photorefractive Effects, Materials, and Devices (2005, July)

The next generation of infrared - sub mm space telescopes requires some reflectors with large dimensions and high quality. These ones, according to weight issues, are based on composite materials for ... [more ▼]

The next generation of infrared - sub mm space telescopes requires some reflectors with large dimensions and high quality. These ones, according to weight issues, are based on composite materials for which the behaviors at low temperatures are badly known. A holographic interferometry method for the verification and validation of this type of reflectors in a space environment is presented. It is based on a dynamic holographic camera observing a diffuser illuminated by the object beam coming from the reflecting surface. Photorefractive crystals being self-processing and reusable mediums, the measuring range of the holographic camera is increased with respect to other optical interferometric methods. The metrological certification of the whole system was realised by the measurement of a parabolic antenna with a 1.1 meter diameter, a known behavior and placed in a simulated space environment [less ▲]

Detailed reference viewed: 47 (2 ULg)
Full Text
See detailSWAP and LYRA: space weather from a small spacecraft
Defise, Jean-Marc ULg; Lecat, Jean-Hervé ULg; Stockman, Yvan ULg et al

in Recent Advances in Space Technologies, 2005. RAST 2005. Proceedings of 2nd International Conference on (2005)

Two scientific instruments for Sun observations are being developed to be part of the payload of the ESA's second microsatellite, Proba-II (Project for On-board Autonomy). PROBA-2 is scheduled for launch ... [more ▼]

Two scientific instruments for Sun observations are being developed to be part of the payload of the ESA's second microsatellite, Proba-II (Project for On-board Autonomy). PROBA-2 is scheduled for launch in early 2007, on a low earth orbit. Like Proba-1, in orbit since October 2001, Proba-2 is a 100-kilogram class spacecraft. PROBA-II will demonstrate new advanced technologies on its scientific payload but also on new platform subsystems such as star tracker, digital Sun sensor, cool gas generator, solar array concentrator, Li-Ion Battery, new central processor, ... This paper is dedicated to the solar payload, comprising the Sun Watcher using Active Pixel System detector and image Processing (SWAP) and the Lyman alpha Radiometer (LYRA), both aiming at Sun observations. SWAP, the Belgian-led main instrument, will continuously provide detailed images of the solar atmosphere, by the light of extreme ultraviolet rays, at 17.4 nm, completely absorbed by the terrestrial atmosphere. SWAP will perform as an operational solar monitoring tool for space weather forecasting while it will also demonstrate new technological solutions: CMOS-APS detector, new off-axis telescope design, athermal structure, ... LYRA (Lyman-alpha Radiometer) is a small compact solar VUV radiometer. This instrument is designed, manufactured and calibrated by a Belgian-Swiss-German consortium. It will monitor the solar flux in four UV passbands. The spectral channels have been carefutly selected for their relevance io space weather, solar physics and aeronomy, ranging from 1 nm to 220 nm. On the technological side, LYRA will benefit from the pioneering UV detectors program using diamond technology. The LYRA data will produce valuable solar monitoring information, for operational space westher nowcasting and research. This paper will detail the instrument concepts and their preparation for delivery to the platform. [less ▲]

Detailed reference viewed: 10 (2 ULg)
Full Text
See detailQualification de grands réflecteurs en environnement spatial
Thizy, Cédric ULg; Stockman, Yvan ULg; Doyle, Dominic et al

in Smigielski, P. (Ed.) Actes du Cinquième colloque francophone Méthodes et Techniques Optiques pour l'Industrie (2004, November)

Les nouvelles générations de télescopes spatiaux dans le domaine infrarouge nécessitent des réflecteurs de grandes dimensions et de haute qualité. Ceux-ci, pour des raisons de poids, sont basés sur les ... [more ▼]

Les nouvelles générations de télescopes spatiaux dans le domaine infrarouge nécessitent des réflecteurs de grandes dimensions et de haute qualité. Ceux-ci, pour des raisons de poids, sont basés sur les technologies des matériaux composites dont les comportements aux basses températures sont mal connus. Une méthode par interférométrie holographique de vérification et de validation en environnement spatial de ce type de réflecteurs est présentée. Elle est basée sur l'utilisation d'une caméra holographique dynamique observant un dépoli sur lequel est projeté le faisceau objet venant de la surface réfléchissante. Outre une augmentation de la dynamique de mesure, cette méthode offre l’avantage principal, par rapport aux techniques d’interférométrie optique, de ne pas nécessiter de système optique d’adaptation du front d’onde au réflecteur à mesurer et donc un gain de flexibilité majeur pour des formes exotiques de réflecteurs (types asphériques). Le système de mesure a été calibré avec un interféromètre ponctuel à effet Doppler. L'influence des différentes sources d’erreur du système sur la mesure a été évaluée. Cette évaluation a porté principalement sur des aspects vibratoires et thermiques. Ces réflecteurs devant être testés sous vide et à basses températures, le système de mesure a été rendu compatible à ces conditions. Des éléments de la caméra holographique (objectifs, CCD, cristal, fibre optique) ont été adaptés et testés sous vide. La certification métrologique de l’ensemble du système sera réalisée par la mesure d'une antenne parabolique, de 1.1 m de diamètre de comportement connu et placée dans un environnement spatial simulé. Le test consistera à mesurer les déplacements et déformations de l'antenne entre un état initial à la température ambiante, et un état final à une température d'environ 130K. [less ▲]

Detailed reference viewed: 57 (7 ULg)
Full Text
See detailFocii determination of an off axis ellipsoid : Theory to practice
Houbrechts, Yvette ULg; Roose, Stéphane ULg; Stockman, Yvan ULg

in Osten, W.; Novak, E. (Eds.) Proceedings of the Eighth International Conference on Laser and Laser Information Technologies (2004, August 02)

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was ... [more ▼]

In the frame of cryogenic test on an off axis ellipsoid, it has been required to set-up an unambiguous method to determine and track the foci position during temperature transitions. This procedure was mandatory to avoid: (1) impact of the operator skills working on triple shift scheme to assure continuously monitoring of the ellipsoid shape during cool down. (2) correctly dissociate the impact of the thermal deformation on the mirror shape with respect to alignment errors. This paper will demonstrate the process, starting from ideal ellipsoid shape, then introducing 3D metrology data in a model, and finally presents the results in a practical situation. [less ▲]

Detailed reference viewed: 28 (1 ULg)
See detailDevelopment of optical ground verification method for mum to sub-mm reflectors
Stockman, Yvan ULg; Thizy, Cédric ULg; Lemaire, Philippe ULg et al

in 5th International Conference on Space Optics (2004, June 01)

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. Scientific ... [more ▼]

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. Scientific observatories require large telescopes with precisely shaped reflectors for collecting the electro-magnetic radiation from faint sources. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of the reflector shapes and antenna structures and to verify their performance under simulated space conditions (vacuum, low temperatures). Due to the specific surface characteristics of reflectors operating in these spectral regions, standard optical metrology methods employed in the visible spectrum do not provide useful measurement results. The current state-of-the-art commercial metrology systems are not able to measure these types of reflectors because they have to face the measurement of shape and waviness over relatively large areas with a large deformation dynamic range and encompassing a wide range of spatial frequencies. 3-D metrology (tactile coordinate measurement) machines are generally used during the manufacturing process. Unfortunately, these instruments cannot be used in the operational environmental conditions of the reflector. The application of standard visible wavelength interferometric methods is very limited or impossible due to the large relative surface roughnesses involved. A small number of infrared interferometers have been commercially developed over the last 10 years but their applications have also been limited due to poor dynamic range and the restricted spatial resolution of their detectors. These restrictions affect also the surface error slopes that can be captured and makes their application to surfaces manufactured using CRFP honeycomb technologies rather difficult or impossible. It has therefore been considered essential, from the viewpoint of supporting future ESA exploration missions, to develop and realise suitable verification tools based on infrared interferometry and other optical techniques for testing large reflector structures, telescope configurations and their performances under simulated space conditions. The first one is an IR-phase shifting interferometer with high spatial resolution. This interferometer shall be used specifically for the verification of high precision IR, FIR and sub-mm reflector surfaces and telescopes under both ambient and thermal vacuum conditions. The second one presented hereafter is a holographic method for relative shape measurement. The holographic solution proposed makes use of a home built vacuum compatible holographic camera that allows displacement measurements from typically 20 nanometres to 25 microns in one shot. An iterative process allows the measurement of a total of up to several mm of deformation. Uniquely the system is designed to measure both specular and diffuse surfaces. [less ▲]

Detailed reference viewed: 10 (3 ULg)