Delphine Faye

The High Time Resolution Spectrometer (HTRS) aboard the International X-ray Observatory (IXO)

The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments of the International X-ray Observatory (IXO). The HTRS is the only instrument matching the top level mission requirement of handling a one Crab X-ray source with an efficiency greater than 10%. It will provide IXO with the capability of observing the brightest X-ray sources of the sky, with sub-millisecond time resolution, low deadtime, low pile-up (less than 2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6 keV). The HTRS is a non-imaging instrument, based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a circular envelope and a X-ray sensitive volume of 4.5 cm2 x 450 μm. As part of the assessment study carried out by ESA on IXO, the HTRS is currently undergoing a phase A study, led by CNES and CESR. In this paper, we present the current mechanical, thermal and electrical design of the HTRS, and describe the expected performance assessed through Monte Carlo simulations.

Syntheses of Zeolite Beta Films in Fluoride Media and Investigation of Their Sorption Properties

Zeolite beta films were synthesized on glass slides and silicon wafers using the secondary growth method. The hydrothermal synthesis was performed in fluoride media with a wide variation of synthesis parameters. The kinetics of crystal growth under different conditions was studied, and film thicknesses ranging between 0.7 and 40 microm were obtained. A synthesis at 160 degrees C for 9 days was found to be the best compromise between the duration and the temperature of crystallization, providing films with thickness of 40 microm. Grazing incidence X-ray diffraction (GID) combined with scanning electron microscopy (SEM) analysis revealed the formation of highly crystalline, randomly oriented films. Sorption capacities and kinetics of the films and corresponding powders were studied toward several organic adsorbents (cyclohexane, n-hexane, p-xylene, trimethylbenzene, tetramethoxysilane). It was found that the adsorbed quantity depends both on the kinetic diameter and on the shape of the molecule, while the sorption capacity of the zeolitic films was estimated to be 7.14 mmol g(-1) of zeolite by nitrogen sorption tests. Kinetics data showed that the adsorption was faster on zeolite powders compared to corresponding films, revealing the presence of additional diffusion barriers in the intergrown layers.

In Situ Real-Time Quantitative and Qualitative Monitoring of Molecular Contamination

The quantitative and qualitative monitoring of contamination is an important issue for the mitigation of the risks induced by contamination. In situ and real-time measurements of contamination levels are currently performed with good accuracy by using quartz microbalances. However, they have to be completed by chemical analyses to identify the nature of the contaminants. Unfortunately, in situ techniques are limited to a very rough characterization. A transfer of the samples is then required, which prohibits real-time monitoring and may lead to the partial degradation of the samples. To tackle this challenge, an experimental technique, coupling thermogravimetric analysis and mass spectrometry, has been developed at ONERA. This method takes advantage of a preseparation of the species through the thermogravimetric analysis. A numerical tool was moreover developed to process automatically experimental thermogravimetric analysis/mass spectrometry data. It enables determination of the contribution of each spec...

Mixture Effects in Contaminant Reemission

The deposit of a pure contaminant or of contaminant mixtures may exhibit complex behavior. This impacts the possible in-flight reemission of these deposits as well as the interpretation of thermogravimetric analyses. These effects were studied, first on theoretical grounds, and then experimentally on controlled mixtures of pure contaminants or uncontrolled mixtures stemming from a real material outgassing. Several effects were clearly identified, such as phase segregation and various mixture behaviors, corresponding to quick or slow diffusion of the contaminants within the mixture.

Aging of Thermal Coatings on Low Earth Orbit: In-Flight Measurements and Modeling

The aging of thermal coatings critically impacts spacecraft thermal balance. Because few in-flight data were available about the aging of materials after a long exposure on sun-synchronous orbit, Centre National d’Etudes Spatiales developed a low-cost experiment called THERME aiming to characterize the evolution of solar absorptivity through a temperature measurement. A data set covering 27 years has thus been generated. The objective of this work is to analyze this very large set of telemetry measurements, taking into account the available satellite parameters (orbit and orientation) and environmental parameters (ultraviolet and atomic oxygen) to identify the most likely causes for the solar absorptivity evolution. To this end, a quantitative model of the evolutions of solar absorptivity has been developed. This model includes the intrinsic degradation of the substrate under ultraviolet radiation, the degradation attributed to contamination, and the erosion of this contamination by atomic oxygen. Althoug...

Ultraviolet Fixation of Molecular Contamination: Physical Model Numerical Implementation and Validation

Physical contamination results from a competition between the deposition of incoming contaminants and their reemission, depending on the surface temperature. However, interaction with ultraviolet light greatly inhibits reemission. Ultraviolet light can lead to chemical reactions, bonding contaminants to the substrate or nearby molecules. This effect can have important consequences in flight. This is especially true for hot surfaces that show no contamination in the absence of ultraviolet light due to their high temperature and can nevertheless be significantly contaminated through photofixation. Previous studies conducted by ONERA–The French Aerospace Lab with Centre National d’Etudes Spatiales allowed identifying the physical mechanisms involved in photofixation and led to a sufficiently simple model to be implemented in engineering software. In this model, the substrate excitation is followed by the reaction of adsorbed contaminants with excited sites. Contaminant chemical photofixation thus results fro...

Zeolite adsorbers for molecular contamination control in spacecraft

Contamination control is an important driver in the success of most space missions with more and more stringent constraints of quality and reliability : indeed, most of spacecrafts having equipments sensitive to molecular contamination like optics or detectors, the risk of damage and performance loss of such sensitive surfaces has to be considered as a real concern and treated in the early phases of the development of an instrument. Since molecular contaminants result mainly from outgassing of polymers, bakeouts under vacuum are required at the lowest possible product level in order to reduce the contamination potential of selected materials. Nevertheless, this conventional method takes time and could be relatively expensive. Then the use of low cost porous materials has appeared as an interesting alternative to trap organic contaminants, taking advantage of their controlled adsorption characteristics in channels of molecular dimensions. A recent PhD study has showed that, compared to other materials, zeolites widely used in catalysis and separation processes have great potential in such applications. Theoretical and experimental investigations have demonstrated the feasibility with three types of highly efficient zeolites. This paper reports on further development related to the preparation of uniform, homogeneous thin films of pure zeolitic materials deposited on different substrates (glass, carbon fibers...). Kinetics and sorption capacities of several representative outgassed species on these films have been investigated by thermogravimetric analyses and the results compared with the efficiency of corresponding powder materials. A discussion on the potential locations of such molecular adsorbers inside optical instruments is proposed.

Prediction of the mechanical properties of zeolite pellets for aerospace molecular decontamination applications

Zeolite pellets containing 5 wt % of binder (methylcellulose or sodium metasilicate) were formed with a hydraulic press. This paper describes a mathematical model to predict the mechanical properties (uniaxial and diametric compression) of these pellets for arbitrary dimensions (height and diameter) using a design of experiments (DOE) methodology. A second-degree polynomial equation including interactions was used to approximate the experimental results. This leads to an empirical model for the estimation of the mechanical properties of zeolite pellets with 5 wt % of binder. The model was verified by additional experimental tests including pellets of different dimensions created with different applied pressures. The optimum dimensions were found to be a diameter of 10–23 mm, a height of 1–3.5 mm and an applied pressure higher than 200 MPa. These pellets are promising for technological uses in molecular decontamination for aerospace-based applications.

Progress in a physical approach to contamination in Europe

Contamination modeling in Europe has long been based on physical mechanisms, such as desorption. However other physical mechanisms, such as diffusion, evaporation or mixing effects exist. These alternative mechanisms were experimentally evaluated and modelled. It was yet observed that, without an experimental capability to reliably separate the (re)emitted chemical species, it is very difficult to determine whether the modeling and its underlying physical mechanisms are representative of reality, or simply a mathematical fit of reality. This is the reason why in the last years emphasis was put on the experimental separation of species, mostly through TGA/MS coupling. This paper presents a review of these efforts and promising results on species separation to reach a really physical modeling of outgassing, deposition/reemission and UV synergy.

Study of performance loss of Lyman alpha filters due to chemical contamination

Observations in the UV and EUV allow many diagnostics of the outer layers of the stars and the Sun so that more and more space telescopes are developed to operate in this fundamental spectral range. However, absorption by residual contaminants coming from polymers outgassing causes critical effects such as loss of signal, spectral shifts, stray light… Thus, a cleanliness and contamination control plan has to be defined to mitigate the risk of damage of sensitive surfaces. In order to specify acceptable cleanliness levels, it is paramount to improve our knowledge and understanding of contamination effects, especially in the UV/EUV range. Therefore, an experimental study has been carried out in collaboration between CNES and IAS, in the frame of the development of the Extreme UV Imager suite for the ESA Solar Orbiter mission; this instrument consists of two High Resolution Imagers and one Full Sun Imager designed for narrow pass-band EUV imaging of the solar corona, and thus very sensitive to contamination. Here, we describe recent results of performance loss measured on representative optical samples. Six narrow pass-band filters, with a multilayer coating designed to select the solar Lyman Alpha emission ray, were contaminated with different amounts of typical chemical species. The transmittance spectra were measured between 100 and 200 nm under high vacuum on the SOLEIL synchrotron beam line. They were compared before and after contamination, and also after a long exposure of the contaminated area to EUV-visible radiations.