A systematic characterization of optical coatings for space application has been carried out to evaluate the performance drop upon low energy protons, ions exposure. This systematic investigation was supported by a project funded by the European Space Agency. Single layers and bi-layers for visible and near-infrared applications have been irradiated with different ions energies and fluences. Moreover, since the irradiation experiments have been performed in large-scale facilities also the flux has been used as a parameter, selecting some values that were a good compromise between the facility occupation time and the real irradiation conditions faced during a space mission. In this work, a summary of the obtained results is reported. Results show that the performance drop is highly dependent on the fluence and the implantation energy, while only for some materials the flux seems to have an effect.

The ESA/JAXA SPICA mission is a candidate for the ESA Cosmic Vision Medium Class M5 opportunity. Since 2019 an Airbus Defence and Space team has been performing a trade-off study (on behalf of ESA) to establish a baseline telescope optical configuration and design, which can meet the mission scientific performance requirements. This paper describes the telescope baseline design selected, with first estimates of the expected optical performance. The optical design wavelength is 20 microns for an operating temperature of 8 K covering a total bandwidth of 12 to 420 microns over a 30 arc minutes field of view, with a total required collecting area of at least 4.0 m². The fundamental mission science driver is to achieve a sky background (astrophysical sources) limited performance. The telescope is designed to illuminate three instruments namely; SMI (JAXA - Japan), SAFARI (SRON - Netherlands) and B-BOP (CEA - France).

Abstract Terrestrial accelerator facilities can generate ion beams which enable the testing of the resistance of materials and thin film coatings to be used in the space environment. In this work, a $$\hbox {TiO}_2$$ TiO 2 /Al bi-layer coating has been irradiated with a $$\hbox {He}^+$$ He + beam at three different energies. The same flux and dose have been used in order to investigate the damage dependence on the energy. The energies were selected to be in the range 4–100 keV, in order to consider those associated to the quiet solar wind and to the particles present in the near-Earth space environment. The optical, morphological and structural modifications have been investigated by using various techniques. Surprisingly, the most damaged sample is the one irradiated at the intermediate energy, which, on the other hand, corresponds to the case in which the interface between the two layers is more stressed. Results demonstrate that ion energies for irradiation tests must be carefully selected to properly qualify space components.

A systematic characterization of dielectric coatings for space application is carried out to evaluate the performance drop upon protons exposure. Different energy levels and fluence values are tested. Also, since the irradiation experiments are performed in large scale facilities, different flux rates are tested to establish the operational parameters that better mimic the real irradiation conditions. The induced damage associated with each irradiation session is characterized for a selection of single and bi-layer coatings. Results show that the performance drop is highly dependent on the fluence and the implantation energy.

Digital Holography (DH) in the Long-Wave InfraRed (LWIR) range shows an increased interest since its first demonstration in 2003 [1]. In particular it allows observing large objects due to the fact that at such wavelengths the ratio between the wavelength and the pixel size allows reconstructing objects 5 to 10 times larger than with DH in visible light [2,3]. We already presented various configurations of LWIR DH interferometry and electronic speckle pattern interferometry for deformation metrology and non destructive testing [3,4]. In this paper we present the application of LWIR DH in interferometric testing of large deformation of large aspheric mirrors in the frame of a European Space Agency project. Here the study focuses on the case of parabolas and ellipses which are usually tested through interferometric wavefront error measurements which require expensive null-lenses matching each of the reflectors considered. In the case of monitoring deformation a holographic technique can be considered where the wavefront is compared with itself at different instants. Therefore the optical set-up can be quite simple and easily reconfigurable from one reflector to another. The advantage of using long wavelength is that large deformations can be measured at once, in addition to being more immune against environmental perturbations. In this paper we review different optical configurations of DH interferometer that led to test a parabolic mirror under thermal-vacuum test [5], as well as an off-axis ellipse tested in laboratory conditions, which is a new result.

The fairing of the launcher selected for the Space Infrared telescope for Cosmology and Astrophysics (SPICA) mission is not compatible with a primary mirror of 3.5m in diameter. Thus three alternative optical designs of the SPICA Telescope Assembly (STA) with a primary mirror of reduced size were defined and their theoretical optical performances assessed. The impact of the size reduction on the STA optical performances was then quantified. Based on the results of the study, we defined a STA optical design optimum in terms of optical performances and of accommodation of instruments in the STA focal surface.

Deformation metrology of complex and large space reflectors is a recurrent problem addressed by ESA. The challenging tasks of on-ground qualification and verification testing are to achieve the required accuracy in the measurement of these reflectors deformation and to verify their performance under simulated space conditions (vacuum, low temperature). A long-wave infrared digital holographic interferometer for the verification and validation of this type of reflector in a space environment is presented. It has been developed to fill the gap between holography/interferometry techniques in the visible wavelengths and methods based on structured light illumination like videogrammetry, stereocorrelation, and fringe/pattern projection. The former provide a good measurement uncertainty but the displacements are often too large to be measured and they require a very stable environment, while the latter provide large measurement range but with higher measurement uncertainty. The new instrument is based on digital holography and uses a CO2 lasers emitting at 10.6μm combined with a commercial thermographic camera. A diffuser is illuminated by the laser beam, producing a speckle wavefront which is observed after reflection on the reflector surface. This reflected speckle wavefront behaves exactly as if the reflector was a diffusive surface, producing its own speckle, allowing the measurement of its deformation. The advantage of this configuration compared to a classical interferometer working at 10.6μm, is that it requires no specific optics such as a null lens (in the case of parabola) or expensive illumination/collection optics (in the case of ellipse). The metrological certification of the system was performed in the laboratory by measuring the tilts of a 1.1 meter diameter parabolic reflector. The displacements are measured in parallel with a Doppler effect interferometer and the measurement uncertainty is estimated. The technique has been certified during a thermal-vacuum test. The deformation of the parabolic reflector is measured for a temperature variation from 288 K down to 113 K. The results are compared to previous results obtained on the same reflector with a high spatial resolution infrared interferometer, also developed at CSL.

We present a portable traceability solution for the ground-based optical calibration of earth observation (EO) instruments. Currently, traceability for this type of calibration is typically based on spectral irradiance sources (e.g. FEL lamps) calibrated at a national metrology institute (NMI). Disadvantages of this source-based traceability are the inflexibility in operating conditions of the source, which are limited to the settings used during calibration at the NMI, and the susceptibility to aging, which requires frequent recalibrations, and which cannot be easily checked on-site. The detector-based traceability solution presented in this work uses a portable filter radiometer to calibrate light sources onsite, immediately before and after, or even during instrument calibration. The filter radiometer itself is traceable to the primary standard of radiometry in the Netherlands. We will discuss the design and realization, calibration and performance verification.

Long-wave infrared digital holographic interferometry with CO2 laser and microbolometer arrays has been developed for testing the large deformations of space reflectors. The setup considered is a Mach-Zehnder, associated to the digital holography reconstruction of the wavefront in the inline configuration with phase shifting. Two possibilities exist for illuminating the tested reflector: either with a point source (similarly to classical interferometry) or an extended source (with a diffuser). This paper presents the development of a modular setup which allows comparing both in the case of a parabolic mirror. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

Out-of-field stray-light spots of the Herschel telescope optics relative to the PACS and SPIRE instrument apertures were modeled by ray tracing simulations with the Advanced Systems Analysis Program (ASAP, by Breault Research Organization) prior to launch. The predicted stray-light behaviour was verified by dedicated stray-light calibration observations in-flight. This resulted in a special feature of the Herschel Science Mission Planning Software, marking the sky positions of stray-light spots by the very bright infrared planetary sources Venus, Mars, Jupiter, and Saturn, as well as the Moon, thus avoiding contamination of scientific photometric observations by out-of-field stray-light of these sources.

Digital holographic interferometry at long infrared wavelengths allows monitoring large deformations of space reflectors during vacuum-thermal testing. We present different optical schemes and an application to the complex case of elliptic reflector.

Digital holographic interferometry in the long-wave infrared domain has been developed by combining a CO(2) laser and a microbolometer array. The long wavelength allows large deformation measurements, which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer, we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test.

Holography and speckle techniques for various metrology and non destructive applications were developed in the 10 µm wavelength range allowing large displacements measurement. Other specific advantages are emphasized like combining temperature and displacement measurement.

Videogrammetry is a 3-dimensional co-ordinate measuring technique that (now) uses digital image capture as the recording method. Images are taken from at least two different locations and the light-rays from the camera to the measurement object are intersected by triangulation into 3D point coordinates. With a large number of images, the camera orientation and 3D point locations are accurately determined with the use of a full mathematical model (bundle adjustment). Adhesive targets are commonly used for point materialization. Those targets consist of a retro-reflective material, with an adhesive backing for sticking to the structure under investigation. A drawback of these types of targets is that they can lose their adhesion and shape during thermal vacuum cycling, especially when cryogenic temperatures are involved. In addition the operation of placing and removing targets is a critical procedure that can lead to undesirable contamination and damage to the test item. Because they require to be physically attached to the surface to be measured, this can also compromise the quality assurance of the test object. Such problems were encountered during cryogenic thermal vacuum qualification testing of the ESA Planck Surveyor mission telescope reflectors. In the development described here the aim was to replace the use of adhesive targets by projected dots. The idea is not fundamentally new. Indeed a US company, Geodetic Systems Inc. (GSI) [1] proposes already a commercial target projector for videogrammetry which uses a flashlamp and is adequate for workshop and laboratory applications. Dot projection videogrammetry is also suggested as a shape measurement method of Gossamer structures, membrane reflectors, etc... [2][3]. Note that there are fundamental differences in use and applications of retro-reflective targets and dot projection: • Retro-reflective targets are materialized on the test article. They appear as fiducials attached to the test article. Any relative distortion of the materialized point can be tracked with respect to the test article itself. • Projected dots are not materialized on the object. Practically a specific point cannot be tracked by this method. The dense cloud of projected dots allows sampling the surface or the shape in an arbitrary way. The Target Projector System (TPS), described here (Fig.1), was designed and manufactured to operate in the Large Space Simulator (LSS) of ESAof ESA under thermal vacuum conditions and to have a minimized temperature exchange with its environment. It is operational over a temperature range of 90K to 350 K, and has a wavelength of 808 nm. Qualification tests and results under vacuum, along with an assessment of the videogrammetric accuracy achievable for various configurations of this unique device are presented.

This presentation describes the challenges of design, fabrication and testing of the 3.5m diameter European Space Agency (ESA) Herschel Space Telescope orbiting since May 2009 around L2. Examples of its outstanding performance are also presented. Article not available.

Deformation metrology of complex space structures and reflectors is a recurrent problem addressed by ESA. Consequently suitable measurement techniques have to be developed and validated to support relevant on-ground qualification and verification testing. For that purpose a novel infrared digital holographic interferometer has been developed to measure the deformation of space reflectors without considering specific optical and expensive components such as null lenses. Laboratory investigations as well as thermal vacuum measurements have been performed to demonstrate the performances of this newly developed interferometer.

One of the aspects that the space and terrestrial terahertz imaging systems have in common is that they require state-of-the-art technology to achieve their ambitious goals. Although technology is advancing at a rapid pace in this frequency range, the requirements for these systems go well beyond what is currently available such that there are also no standards or calibration reference sources in this field. This paper describes the novel procedures that have been implemented to assess the "in-orbit" RF performance of two European Space Agency (ESA) satellites using on-ground verification procedures. These consisted of using several different measurement techniques at both ambient and cryo-temperatures and software model correlation to be able to predict the final performance. ESA's Herschel and Planck observatories are used as an example to highlight some of the hurdles that had to be overcome for the challenging task of flight-performance verification at (sub)millimeter-wave frequencies. Significant advances have been achieved despite the lack of internationally agreed procedures and practices pushing terahertz reflector and instrument technologies to new limits. This is a review paper and has been written on behalf of the large scientific, engineering, and management teams that were involved over many years in the development, production, testing, and operation of the two spacecraft

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory offering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55-671 {\mu}m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.