Deformation analysis of ATHENA test filters made of plastic thin films supported by a mesh under differential static pressure

Within ESA Cosmic Vision 2015-2025 Science Program, ATHENA was selected to be a Large-class high energy astrophysics space mission. The observatory will be equipped with two interchangeable focal plane detectors named X-Ray Integral Field Unit (X-IFU) and Wide Field Imager (WFI). In order to optimally exploit the detector sensitivity, X-ray transparent filters are required. Such filters need to be extremely thin to maximize the X-ray transparency, that is, no more than a few tens of nm, still they must be able to sustain the severe stresses experienced during launch. Partially representative test filters were made with a thin polypropylene film, coated with Ti, and supported by a thin highly transparent mesh either in stainless steel or niobium. Differential static pressure experiments were carried out on two filter samples. In addition, the roles of the mesh on the mechanical deformation is studied, adopting a finite element model (FEM). The numerical analysis is compared with experimental results and found in good agreement. The FEM is a promising tool that allows to characterize materials and thicknesses in order to optimize the design

X-IFU Filter Wheel Optical Blocking Filters Technology Demonstration Plan

The main purpose of the present plan is to provide a clear path to demonstrate the TRL5 by the Mission Adoption for the three OBFs on the X-IFU Filter Wheel (FW). An effort has been performed in trying to identify what shall be considered technology, for which the maturity has to be demonstrated, and what is design that can still contribute to improve the performances of the FW filters along phases B and C of development. The X-IFU FW filters conceptual design is similar to that defined (during phase A) and described in the "X-IFU Filter Wheel Mechanism and Electronics Design Description", and the "X-IFU Thermal Filters (THFs) Description" documents presented at the I-PRR. The preliminary design of the X-IFU FW Filters rely on heritage from previous missions and characterization tests performed in phase-A on breadboards manufactured by LUXEL Corporation (Friday Harbor, WA, USA). The adoption of a design similar to that of the X-IFU THFs for frame shape and materials, and to that of the WFI FW filters for film and coating thicknesses, as well as for overall dimensions, allow migrating part of the achievements reached by the X-IFU THFs and WFI FW filters to the X-IFU FW filters. For this reason, the TDP for the X-IFU FW filters will be mainly focused on the vibro-acoustic performances. With this respect, minor effort will be dedicated to the thick and very robust meshless filter (25 μm PI + 100 nm Al) designed to observe very bright x-ray sources. The goal of this activity is to demonstrate TRL5 before MAR for the baseline technology of filters manufactured by LUXEL (PI/Al on BeCu mesh). However, in parallel to verify also the maturity of other filter technologies and to mitigate the risks of having only one manufacturer, we will procure and test filter samples and bare meshes of other European manufacturers (OXFORD instruments, XRNanotech). The identified TECHNOLOGY development elements that we consider critical in the X-IFU FW OBFs are described in this document. In section 7 we list the breadboards (BBs) we have identified to perform the necessary characterization tests aimed at demonstrating their maturity

Coronal energy release by MHD avalanches II. EUV line emission from a multi-threaded coronal loop

Funding: GC, PP, and FR acknowledge support from ASI/INAF agreement n. 2022-29-HH.0. This work made use of the HPC system MEUSA, part of the Sistema Computazionale per l’Astrofisica Numerica (SCAN) of INAF-Osservatorio Astronomico di Palermo. JR and AWH acknowledge the financial support of Science and Technology Facilities Council through Consolidated Grant ST/W001195/1 to the University of St Andrews. PT was supported by contract 4105785828 (MUSE) to the Smithsonian Astrophysical Observatory, and by NASA grant 80NSSC20K1272x.Context. Magnetohydrodynamic (MHD) instabilities, such as the kink instability, can trigger the chaotic fragmentation of a twisted magnetic flux tube into small-scale current sheets that dissipate as aperiodic impulsive heating events. In turn, the instability could propagate as an avalanche to nearby flux tubes and lead to a nanoflare storm. Our previous work was devoted to related 3D MHD numerical modeling, which included a stratified atmosphere from the solar chromosphere to the corona, tapering magnetic field, and solar gravity for curved loops with the thermal structure modelled by plasma thermal conduction, along with optically thin radiation and anomalous resistivity for 50 Mm flux tubes. Aims. Using 3D MHD modeling, this work addresses predictions for the extreme-ultraviolet (EUV) imaging spectroscopy of such structure and evolution of a loop, with an average temperature of 2–2.5MK in the solar corona. We set a particular focus on the forthcoming MUSE mission, as derived from the 3D MHD modeling. Methods. From the output of the numerical simulations, we synthesized the intensities, Doppler shifts, and non-thermal line broadening in 3 EUV spectral lines in the MUSE passbands: Fe ix 171 Å, Fe xv 284 Å, and Fe xix 108 Å, emitted by ~1MK, ~2MK, and ~10MK plasma, respectively. These data were detectable by MUSE, according to the MUSE expected pixel size, temporal resolution, and temperature response functions. We provide maps showing dierent view angles (front and top) and realistic spectra. Finally, we discuss the relevant evolutionary processes from the perspective of possible observations. Results. We find that the MUSE observations might be able to detect the fine structure determined by tube fragmentation. In particular, the Fe ix line is mostly emitted at the loop footpoints, where we might be able to track the motions that drive the magnetic stressing and detect the upward motion of evaporating plasma from the chromosphere. In Fe xv, we might see the bulk of the loop with increasing intensity, with alternating filamentary Doppler and non-thermal components in the front view, along with more defined spots in the topward view. The Fe xix line is very faint within the chosen simulation parameters; thus, any transient brightening around the loop apex may possibly be emphasized by the folding of sheet-like structures, mainly at the boundary of unstable tubes. Conclusions. In conclusion, we show that coronal loop observations with MUSE can pinpoint some crucial features of MHD-modeled ignition processes, such as the related dynamics, helping to identify the heating processes.Peer reviewe

Technical Note 10 – Filter Characterization Report

This document describes the main results obtained from characterization measurements performed on different filter samples designed and manufactured within this contract. Thin films of silicon nitride and polyimide of different sizes (ranging from 10 to 100 mm), shape (circular or square) and mechanical design (e.g. meshless or supported by Si or polyimide meshes) have been manufactured within this contract to investigate new solutions to build optical blocking filters for X-ray detectors in future space applications. In addition, preliminary measurements have been performed on a new material based on CNT which will be further investigated in a CCN of this contract. The characterization measurements, obtained with a suite of different techniques, provide very useful results for future developments of the investigated materials

Development of processes and tests for the creation of the Primary Mirror and the Flexure Hinges for the Ariel Space Telescope

The ESA's Ariel space mission, scheduled for launch in 2029, aims to study the atmospheres of ~ 1000 exoplanets in the wavelengths between Visible and Infrared. Ariel's telescope, to the Cassegrain off-axis type, will employ an elliptical primary mirror with a parabolic surface measuring 1.2x0.7m, entirely made of Aluminum 6061T651 alloy. Notably, this marks the first instance of manufacturing a primary mirror of such dimensions in aluminum for Infrared applications, and this required a comprehensive study of production processes. Additionally, aluminum flexure hinges have been designed and tested to ensure an optimal connection between the primary mirror and the optical bench, minimize optical surface deformation due to its low density, maximize heat exchange, and maintain a high degree of structural robustness. This work describes all the development processes and tests to realize the primary mirror and flexure hinges. These activities will provide a solid foundation for future space missions.</p

Development, manufacturing, and testing of Ariel’s structural model prototype flexure hinges

The Atmospheric Remote-Sensing Infrared Exoplanet Large Survey (Ariel) is the M4 mission adopted by ESA's "Cosmic Vision" program. Its launch is scheduled for 2029. The mission aims to study exoplanetary atmospheres on a target of ∼ 1000 exoplanets. Ariel's scientific payload consists of an off-axis, unobscured Cassegrain telescope. The light is directed towards a set of photometers and spectrometers with wavebands between 0.5 and 7.8 μm and operating at cryogenic temperatures. The Ariel Space Telescope consists of a primary parabolic mirror with an elliptical aperture of 1.1· 0.7 m, all bare aluminum. To date, aluminum mirrors the size of Ariel's primary have never been made. In fact, a disadvantage of making mirrors in this material is its low density, which facilitates deformation under thermal and mechanical stress of the optical surface, reducing the performance of the telescope. For this reason, studying each connection component between the primary mirror and the payload is essential. This paper describes, in particular, the development, manufacturing, and testing of the Flexure Hinges to connect Ariel's primary Structural Model mirror and its optical bench. The Flexure Hinges are components already widely used for space telescopes, but redesigning from scratch was a must in the case of Ariel, where the entire mirror and structures are made of aluminum. In fact, these flexures, as well as reducing the stress due to the connecting elements and the launch vibrations and maintaining the alignment of all the parts preventing plastic deformations, amplified for aluminum, must also have resonance frequencies different from those usually used, and must guarantee maximum contact (tolerance in the order of a micron) for the thermal conduction of heat. The entire work required approximately a year of work by the Ariel mechanical team in collaboration with the industry

Analysis and characterization of mid-spatial frequency surface errors on the mirrors of the ariel space telescope

The Atmospheric Remote-Sensing Infrared Exoplanet Large Survey (Ariel) is ESA's M4 mission of the "Cosmic Vision" program, with the purpose of surveying the atmospheres of a large sample of known exoplanets through transit spectroscopy. Launch is scheduled for 2029. Ariel is based on a 1 m class telescope optimized for spectroscopy in the waveband between 1.95 and 7.8 μm, operating at cryogenic temperatures in the range 40-50 K. The Ariel Telescope is an off-axis, unobscured Cassegrain design, consisting of four mirrors and feeding a collimated optical beam to a set of spectrometers and photometers. The mirrors and all telescope supporting structures are realized in the aerospace-grade aluminum alloy T6061 to facilitate thermalization. Specific characteristics of the material, however, pose unique challenges to mirrors manufacturing. The softness and specific microscopic features of the aluminum alloy make it difficult to achieve an optimum balance between surface shape and low microroughness, while minimizing at the same time the presence of "waviness", that is surface shape errors in the middle range of spatial frequencies. This work describes the initial analyses and simulations performed during the first phases of development of the processes employed for the grinding and polishing of the mirror prototypes, with particular regard to the characterization of the mid-spatial frequency errors and a study of the effects of such errors on telescope performance.</p

Aluminum based large telescopes: the ARIEL mission case

Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large Survey) is the adopted M4 mission of ESA “Cosmic Vision” program. Its purpose is to conduct a survey of the atmospheres of known exoplanets through transit spectroscopy. Launch is scheduled for 2029. Ariel scientific payload consists of an off-axis, unobscured Cassegrain telescope feeding a set of photometers and spectrometers in the waveband between 0.5 and 7.8 µm, and operating at cryogenic temperatures. The Ariel Telescope consists of a primary parabolic mirror with an elliptical aperture of 1.1 m of major axis, followed by a hyperbolic secondary, a parabolic recollimating tertiary and a flat folding mirror. The Primary mirror is a very innovative device made of lightened aluminum. Aluminum mirrors for cryogenic instruments and for space application are already in use, but never before now it has been attempted the creation of such a large mirror made entirely of aluminum: this means that the production process must be completely revised and fine-tuned, finding new solutions, studying the thermal processes and paying a great care to the quality check. By the way, the advantages are many: thermal stabilization is simpler than with mirrors made of other materials based on glass or composite materials, the cost of the material is negligeable, the shape may be free and the possibility of making all parts of the telescope, from optical surfaces to the structural parts, of the same material guarantees a perfect alignment at whichever temperature. The results and expectations for the flight model are discussed in this paper