Sentinel-5/UVNS instrument is an Earth atmospheric monitoring spectrometer developed within the Copernicus program. The mission objective is to monitor the chemical composition of the Earth’s atmosphere on a daily basis. Airbus Defense and Space GmbH acts as the prime contractor for the instrument under a European Space Agency contract. The current paper will focus on four themes. First it will provide a brief historical and technical overview of the Sentinel-5/UVNS instrument. Second, the key design drivers will be described. Third, the key optical technologies carried on board the instrument will be elaborated. Finally, the paper concludes with a short look at the current state of the instrument’s development cycle.

PROBA-3 is a mission devoted to the in-orbit demonstration (IOD) of precise formation flying (F²) techniques and technologies for future ESA missions. The mission includes two spacecraft. One of them will act as an external occulter for scientific observations of the solar corona from the other spacecraft, which will hold the ASPIICS coronagraph instrument, under CSL responsibility. The ASPIICS instrument on PROBA-3 looks at the solar corona through a refractive telescope, able to select 3 different spectral bands: Fe XIV line @ 530.4nm, He I D3 line @587.7nm, and the white-light spectral band [540;570nm]. The external occulter being located at ~ 150 meters from the instrument entrance, will allow ASPIICS to observe the corona really close to the solar limb, probably closer than any internally or externally occulted coronagraph ever observed. This paper will present the straylight model and analyses carried out by CSL. A first specificity of the analysis is that the scene on the useful Field of View (FOV) is the solar corona which has a brightness dynamic range as high as 103 between the close corona, close to 1 solar radius (Rsun), and the “distant” corona around 3RSun. The specifications are very stringent for this type of instrument. A consensus was found and will be presented regarding the expected straylight within the FOV. It will also be shown that to achieve realistic estimations it is required to take into account the exact location of the created straylight as well as the entrance field. The second specificity that had to be analyzed is that the diffraction from the solar disk by the external occulter enters the instrument un-obstructed until the internal occulter, and with a brightness 100 times higher than the close corona (~1RSun) brightness. The simulation of this diffraction as well as its propagation inside the ASPIICS telescope creating additional straylight, had to be carefully established in order to give realistic results of its impact on the performances while being actually possible to compute.

Sentinel-5/UVNS instrument is an Earth atmospheric monitoring spectrometer developed within the Copernicus program. The mission objective is to monitor the chemical composition of the Earth’s atmosphere on a daily basis. Airbus Defense and Space GmbH acts as the prime contractor for the instrument under a European Space Agency contract. The current paper will focus on four themes. First it will provide a brief historical and technical overview of the Sentinel-5/UVNS instrument. Second, the key design drivers will be described. Third, the key optical technologies carried on board the instrument will be elaborated. Finally, the paper concludes with a short look at the current state of the instrument’s development cycle.

Multi-spectral optical filters are essential parts of spaceborne optical imagers such as the Multispectral Instrument (MSI) for the Sentinel-2 satellite in the framework of ESA’s GMES programme for earth observation. In this development, Jena-Optronik is responsible for the design, manufacturing and test of the spectral filter assemblies. They are the key elements that define the spectral quality of the instrument. Besides the challenging spectral requirements straylight aspects are of crucial importance due to the close neighbourhood of the filter elements to the detector. Results will be presented of the extensive analyses and measurements that have been performed on component and assembly level to ensure the optical performance.

The presentation provides a synthesis of the alignment and the measured performance of the PFM telescope of the Multispectral Instrument.

Ingenio/SEOSAT is a high-spatial-resolution optical mission developed under the Spanish Earth Observation National Program for Satellites (PNOTS), and managed technically in the framework of an ESA contract. It features as Primary Payload (PP) a high-resolution optical payload with one 2.5 meter resolution panchromatic channel and four 10 meter resolution visible/near infrared spectral channels. It is based on a twin Korsch telescope concept, each telescope covering half of the instrument's swath width. In this communication is presented a detailed account of the work performed to accurately characterize and correct by post-processing an image ghost present in the multi-spectral channels of the primary payload. The work reported here includes the description and analysis of the results of three test campaigns, performed at Thales Alenia Space. Tests carried out include radiometric tests at focal plane level, generic stray-light tests and a novel test to characterize specifically the parameters of the studied cross-talk image ghost. Field-dependent point spread functions for the studied image ghost have been generated by optical analysis, and have been adjusted with the results of the performed tests. From these, image filters have been devised to reproduce, and remove by subtraction, the image ghost. Quantitative image ghost correction results on an actual test image are shown.

The Gaia all-sky astrometric survey is challenged by several issues affecting the spacecraft stability. Amongst them, we find the focus evolution, straylight and basic angle variationsContrary to pre-launch expectations, the image quality is continuously evolving, during commissioning and the nominal mission. Payload decontaminations and wavefront sensor assisted refocuses have been carried out to recover optimum performance. An ESA-Airbus DS working group analysed the straylight and basic angle issues and worked on a detailed root cause analysis. In parallel, the Gaia scientists have also analysed the data, most notably comparing the BAM signal to global astrometric solutions, with remarkable agreement.In this contribution, a status review of these issues will be provided, with emphasis on the mitigation schemes and the lessons learned for future space missions where extreme stability is a key requirement.

One of the technological challenges of direct observation of extra-solar planets by nulling interferometry is the development of a modal filter operating from 6 to 20 mu m. In the present paper a candidate technology for the fabrication of such modal filters is presented: Integrated Optics. A solution based on alltelluride buried channel waveguides is considered. In the proposed waveguides, vertical guiding of light is achieved by a 15 mu m-thick Te83Ge17 core film deposited onto a lower-index Te75Ge15Ga10 substrate, and covered by a 15 mu m-thick Te76Ge24 superstrate. Horizontal guiding of light is obtained by modifying the geometry of the core layer by ion beam etching.As this stage, all-telluride buried channel waveguide prototypes demonstrate light guiding and transmission from 2 to 20 mu m. The validity of the technology and the good quality of the fabrication process, in particular the input and output facets surface finish are thus confirmed. These results consolidate the potential of Te-based integrated optics components for nulling interferometry. (C) 2015 Elsevier B.V. All rights reserved.

In the framework of development of ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), the Centre Spatial de Liege is responsible of the optical design of the coronagraph and the optics will be manufactured by TOPTEC.The particularity of this coronagraph is to have an external occulter located 150 m ahead of the first imaging lens. This external occulter is re-imaged on an internal occulter which function is - as in a classical externally occulted Lyot coronagraph - to block the sun light diffracted by the external occulter and to reduce the straylight on the detector. The selection of this configuration is driven by the requirement to observe the corona as close as possible to the solar limb (i.e. 1 R-Sun) without imaging the limb itself. A requirement of 1.08 R-Sun is specified at optical design level to grant 1.2 R-sun at instrument level. The coronograph instrument is designed to have a field of view of 1.6 degrees x 1.6 degrees with a resolution of less than 6 arcsec. Its performances are limited by diffraction in a 530 - 590 nm wavelength range.This paper presents the optical design and demonstrates that by design the requirements are fulfilled within the misalignment, manufacturing and thermo-elastic error contributions.

The Sentinel 2 mission shall ensure the continuity and enhancement of Landsat and SPOT data and sustain operational land services in the frame of the Global Monitoring for Environment and Security (GMES) initiative. Sentinel-2 is designed to image the Earth’s landmasses from its orbit for at least 7.25 years. The Multi-Spectral Instrument (MSI), delivered by Astrium Toulouse, will provide high resolution imagery in 13 spectral channels extending from the Visible Near Infrared (VNIR, 400-1100 nm) to the Short Wave Infra-Red (SWIR, 1100-2500 nm) range, down to a resolution of 10 meters with an image width of 290 kilometers. A dichroic splitter device is located in back-focal path of the telescope. It allows splitting the incoming optical beam between VNIR and SWIR focal planes. It shall ensure an extremely high rejection, better than 1:1000, between both ranges while introducing negligible aberrations in reflected (VNIR) and transmitted (SWIR) paths. The splitter assembly consists of a wedged dichroic filter plate and a wedged compensator plate mounted in a common frame. Both plates are made of fused silica (Infrasil) and polished to lambda/40. The major challenges reside in the design complexity of the dichroic coating and in the deposition process control to ensure the required high uniformity of performances through the large aperture. The paper presents the final spectral and optical performances of this challenging sub-system. It also discusses the main difficulties that have been overpassed during the development and qualification phase.

In the framework of the “Integrated Optics” project, single-mode RIB waveguides for both [6–11µm] and [10–20µm] spectral bands were developed in order to manufacture modal filters for spatial interferometry. In this paper, the different steps of the fabrication of such components are described and the first results in term of light guiding and modal filtering are presented.

This paper summarises the work done over the last few years on the prediction of the RF performance of the Planck telescope, which was done initially to support the design phase, and later to assess compliance to specifications and to infer the in-flight performance of the telescope once in its operational orbit.

Nulling interferometry is a technique providing high angular resolution which is the core of the space missions Darwin and TPF. The first objective is to reach a deep degree of starlight cancelation in the range 6–20μm, in order to observe and to characterize the signal from an earth-like planet. Among the numerous technological challenges involved in these missions, the question of the beam combination and wavefront filtering has an important place. A single-mode integrated optics (IO) beam combiner could support both the functions of filtering and the interferometric combination, simplifying the instrumental design. Such a perspective has been explored in this work within the project Integrated Optics for Darwin (IODA), which aims at developing a first IO combiner in the mid-infrared. The solutions reviewed here to manufacture the combiner here are based on infrared dielectric materials on one side, and on metallic conductive waveguides on the other side. With this work, additional inputs are offered to pursue the investigation on mid-infrared photonics devices.

This paper addresses the interferometric measurements performed on PLANCK Secondary reflector-Flight Model (SRFM) during the cryo-optical test at the Centre Spatial de Liege in Belgium. It was 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 selected and a dedicated thermo mechanical set-up has been constructed. One emphasizes on the solutions adopted to cope with high surface slopes appearing at cryogenic temperature. Indeed, detector resolution has been exploited to resolve high density fringes at the expense of the aperture. A stitching procedure has been implemented to reconstruct the full aperture measurement with success. Test results are presented.

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 mu m 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.

This paper summarizes the results of an ESA feasibility study of a Wide-Field Optical Infrared Imager (WFI) that would search for Type Ia supernovae at low redshift with the aim to measure the changing rate of expansion of the universe. WFI multi-spectral images of the deep universe could also benefit to many other research area in astrophysics. The WFI payload includes a 2 m class telescope, a 1 square degree field of view imaging camera and a low-resolution integral field spectrometer. A mission concept was identified that consists of

Specular and diffuse reflectance (BRDF) of black absorbing coatings, meant to be used for the HIFI instrument aboard the FIRST satellite, has been studied in the sub-millimetre region (0.1<lambda<0.9mm). These coatings have to meet space qualification requirements and must be usable for at least the overall wavelength band (0.1-0.6mm) covered by the MFI spectrometer. Existing materials, coatings obtained from other research groups and home made samples have been studied. Optical characterisation of these coatings has been performed at wavelengths of 96.5 mu m, 118.8 mu m, 184.3 mu m, 496 mu m and 889 mu m, for a large range of directions of incident and reflected light and for different polarisation directions. A limited number of reflectance measurements at cryogenic temperatures have been carried out too. A simple experimental set up to study the effect of double scattering has been constructed to investigate the accuracy of numerical simulations based on experimental BRDF values. Data show that the best samples (home made) have BRDF values below about 2.10(-2) Sr-1 throughout the wavelength range of interest, quite independent of directions of incidence, reflection and polarisation. The Total Hemispherical Reflection of such a coating will then be 0.06.

Light scattering measurements are important tools for characterizing optical surfaces can basically be divided into two main groups: total scatter measurements (TS) and Angle Resolved Scattering (ARS). Since TS measurements are fairly straight forward and widely used, international standardization has formulated an international draft standard on it, ISO/DIS 13696. ARS is a more complex method and not as common as TS measurements. However ARS data in form of the Bi-directional Reflectance Distribution FUnction (BRDF) can be used to predict stray light in Laser and Industrial Optical Systems. Because of increasing importance of this topic the EC is sponsoring a project regarding 'Standard procedures for stray light specification, measurement and testing - SLIOS'. During the project two of the activities are: performing a round robin experiment of measuring BRDF data at 5 different sites including some complementary techniques; compiling of an open access data base of measured BRDF data, measured according to procedures agreed upon between the SLIOS partners and proposed for 'Standard Procedures'. Results of these two activities will be presented.