For several decades, the field of X-ray astronomy has been playing a major role in understanding the processes in our universe. From binary stars and black holes up to galaxy clusters and dark matter, high energetic events have been observed and analysed using powerful X-ray telescopes like e.g. Rosat, Chandra, and XMM-Newton [1,2,3], giving us detailed and unprecedented views of the high-energy universe.
In November 2013, the theme of “The Hot and Energetic Universe” was rated as of highest importance for future exploration and in June 2014 the ATHENA Advanced Telescope for High Energy Astrophysics was selected by ESA for the second large science mission (L2) in the ESA Cosmic Vision program, with launch foreseen in 2028 . By combining a large X-ray telescope with state-of-the-art scientific instruments, ATHENA will address key questions in astrophysics, including: How and why does ordinary matter assemble into the galaxies and galactic clusters that we see today? How do black holes grow and influence their surroundings?
In order to answer these questions, ATHENA needs a powerful mirror system which exceed the capabilities of current missions, especially in terms of collecting area. However, current technologies have reached the mass limits of the launching rocket, creating the need for more light-weight mirror systems in order to enhance the effective area without increasing the telescope mass. Hence new mirror technologies are being developed which aim for low-weight systems with large collecting areas. Light material like glass can be used, which are shaped to form an X-ray reflecting system via the method of thermal glass slumping.
The paper provides a description of recent progress in the development of lightweight, precision and highthroughput grazing-incidence mirrors for X-ray astronomy made of glass. In particular, the indirect slumping technology under investigation at the Max Planck Institute for Extraterrestrial Physics (MPE) is reviewed and recent activities are presented together with the research approach. The glass slumping technique foresees several steps: a thermal forming process using a suitable mould; a reflective layer application; the alignment and integration of mirror segments into a supporting structure; and the final verification of prototype modules using X-rays. Each step is considered at MPE, with the involvement of partner institutes and universities. The last year of activities was mainly dedicated to the procurement of new moulds and to the application of Iridium coating. The main results will be presented.
The Slumping Glass Optics technology for the fabrication of astronomical X-ray mirrors has been developed in recent years in USA and Europe. The process has been used for making the mirrors of the Nustar, mission. The process starts with very thin glass foils hot formed to copy the profile of replication moulds. At INAF - Osservatorio Astronomico di Brera a process based on cold shaping is being developed, based on an integration method involving the use of interconnecting ribs for making stacks. Each glass foil in the stack is shaped onto a very precise integration mould and the correct shape is frozen by means of glued ribs that act as spacers between one layer and the next one (the first layers being attached to a thick substrate). Therefore, the increasing availability of flexible glass foils with a thickness of a few tens of microns (driven by electronic market for ultra-thin displays) opens new possibilities for the fabrication of X-ray mirrors. This solution appears interesting especially for the fabrication of mirrors for hard X-rays (with energy > 10 keV) based on multilayer coatings, taking advantage from the intrinsic low roughness of the glass foils that should grant a low scattering level. The stress frozen on the glass due to the cold shaping is not negligible, but it is kept into account in the errors of the X-ray optics design. As an exercise, we have considered the requirements and specs of the FORCE hard Xray mission concept (being studied by JAXA) and we have designed the mirror modules assuming the cold slumping as a fabrication method. In the meantime, a prototype (representative of the FORCE mirror modules) is being design and integrated in order to demonstrate the feasibility and the capacity to reach good angular resolution.
Large X-ray telescopes for future observatories need to combine a big collecting area, meaning thin mirrors with large diameter, with good angular resolution. Structures have to be stiff enough to guarantee the correct profiles and positioning of such mirrors. Due to the mass limits of the launching rockets, lightweight materials and configurations are required.. The Slumped Glass Optic (SGO) group of the Max-Planck-Institute for Extraterrestrial physics (MPE) is developing the indirect slumping technology to comply with this need. This technique foresees the shaping at high temperature of thin glass foils, originally flat, to Wolter I design X-ray mirror segments, by using suitable moulds. During the thermal cycle inside an electrical oven the glass viscosity is such reduced that it allows its bending onto the mould. So the mould’s shape is replicated while still maintaining the original micro-roughness of the glass on the non-contact side that is of fundamental importance for X-ray reflections. This replication process is particularly suitable for the manufacturing of several identical optical elements, which must successively be coated with the necessary reflective layer and then aligned and integrated into supporting structures. Numerous aspects of the technology have been studied in the past, such as the selection of mould and glass materials, and the corresponding optimization of the thermal cycle parameters. During the last year, we focused on different process set-ups. The current results and status of activities will be presented in the paper.
The Slumped Glass Optic (SGO) group of the Max Planck Institute for Extraterrestrial physics (MPE) is studying the indirect slumping technology for its application to X-ray telescope manufacturing. Several aspects of the technology have been analyzed in the past. During the last months, we concentrated our activities on the slumping of Schott D263 glass on a precise machined Fused Silica mould: The concave mould was produced by the Italian company Media Lario Technologies with the parabola and hyperbola side of the typical Wolter I design in one single piece. Its shape quality was estimated by optical metrology to be around 6 arcsec Half Energy Width (HEW) in double reflection. The application of an anti-sticking Boron Nitride layer was necessary to avoid the adhesion of the glass on the mould during the forming process at high temperatures. The mould has been used for the slumping of seven mirror segments 200 mm long, 100 mm wide, and with thickness of 200 μm or 400 μm. The influence of the holding time at maximum temperature was explored in this first run of tests. The current results of the activities are described in the paper and plans for further investigations are outlined.
The Max-Planck-Institute for Extraterrestrial Physics (MPE) is involved in the investigation and optimization of the indirect slumping technique for the manufacturing of thin glass mirror segments to be assembled in lightweight X-ray telescopes. During the last year, we started to analyze the influence of vacuum environment on the results of this thermal forming process. The realization of slumping in vacuum offers theoretically several advantages, like the absence of air between the glass and the mold and a cleaner process chamber. Furthermore, the heat exchange is different with respect to a standard air-oven and this might have positive effects during the important heating and cooling phases of the process. All these aspects will be considered in the paper and the current status in the development of the MPE vacuum-slumping approach will be outlined.
The Slumped Glass Optics technology, developed at INAF/OAB since a few years, is becoming a competitive solution for the realization of the future X-ray telescopes with a very large collecting area, as e.g. the proposed Athena, with more than 2 m2 effective area at 1 keV and with a high angular resolution (5’’ HEW). The developed technique is based on modular elements, named X-ray Optical Units (XOUs), made of several layers of thin foils of glass, previously formed by direct hot slumping in cylindrical configuration, and then stacked in a Wolter-I configuration, through interfacing ribs. The achievable global angular resolution of the optics relies on the surface shape accuracy of the slumped foils, on the smoothness of the mirror surfaces and on the correct integration and co-alignment of the mirror segments achieved with a dedicated Integration Machine (IMA). In this paper we provide an update of the project development, reporting on the last results achieved. In particular, we will present the results obtained with full illumination X-ray tests for the last developed prototypes.
Future X-ray telescopes aim for large effective area within the given mass limits of the launcher. A promising method is the hot shaping of thin glass sheets via a thermal slumping process. This paper presents the status and progress of the indirect glass slumping technology developed at the Max-Planck-Institut for extraterrestrial Physics (MPE). Recent developments in our research include the use of the mould material Cesic under vacuum, as well as the fabrication of a high-precision slumping mould, which meets the requirements of large, high angular resolution missions like ATHENA. We describe the way forward to optimise the slumping process on these materials, the force-free integration concept and its progress, as well as the first test on reflective coating application.
For several years, the Max-Planck-Institute for extraterrestrial Physics in Germany (MPE) and the Astronomical Observatory of Brera in Italy (INAF-OAB) have been studying the slumping technology for the manufacturing of segmented glass X-ray optics for astronomy. Despite some differences in their specific approaches, the synergy of the two institutes has always been good, focusing on the common goal of developing a technology able to meet the outstanding requirements for future X-ray telescopes: i.e. large collecting areas, low mass and good angular resolution. This synergy has in the last year resulted in an active collaboration for the production of a Joint Integrated Module (JIM) that puts together the expertise of the two research groups. In particular, the indirect slumping approach of MPE has been employed for the manufacturing of X-ray mirror segments that have been integrated into a kind of X-ray Optical Unit following the approach developed at INAF-OAB. The module has then been tested in X-ray at the MPE PANTER facility, in Neuried. The several steps and the results of this joint activity are reviewed and discussed in this paper.
The indirect hot slumping technology is being developed at Max-Planck-Institute for extraterrestrial Physics (MPE) for the manufacturing of lightweight astronomical X-ray telescopes. It consists of a thermal shaping process to replicate the figure of a suitable mould into segments of X-ray mirror shells made by glass. Several segments are aligned and mounted into elemental modules, a number of which is then assembled together to form the telescope. To obtain mirror segments of high optical quality, the realization of the slumping thermal cycle itself is of fundamental importance, but also the starting materials, primarily the mould and the glass foils, play a major role. This paper will review the MPE approach in the slumping technology development and will then concentrate on the glass, with particular regards to the problem of thickness variation.
Large X-ray telescopes for future observations need to combine a big collecting area with good angular resolution. Due to the mass limits of the launching rocket, light-weight materials are needed in order to enhance the collecting area in future telescopes. We study the development of mirror segments made from thin glass sheets which are shaped by thermal slumping. At MPE we follow the indirect approach which enables us the production of the parabolic and hyperbolic part of the Wolter type I mirrors in one piece. In our recent research we have used a test mould made of CeSiC™ for slumping processes in our lab furnace as well as in a heatable vacuum chamber, to avoid oxidation and air enclosure. Additional slumping tests in the vacuum furnace have been carried out using a Kovar mould and are compared with results under air. We describe the experimental set-up, the slumping process and the metrology methods and give an outlook on future activities.
This paper provides an update on the current activities for alignment and integration of slumped glass x-ray mirrors at MPE. Progress is being made w.r.t. the integration facility which is currently transitioned from a manual bench top setup to a full scale robotic system based on a high precision hexapod and collimated beam metrology. We present the most important design considerations and features of this new system as well as progress on other details of the integration concept.
The demand for larger collecting areas in X-ray telescopes within the mass limits of the launcher creates the need for light-weight mirror materials. At our institute we develop the technology of indirect thermal slumping of thin glass sheets to manufacture light mirror segments. A crucial part of the development is the measurement of the glass surface, shape and thickness profile in order to evaluate the quality of the reproduction method. We describe the measurement set-up, the analysis method of the surface profile and the evaluation of thickness variations in the glass, as well as their influence on the final glass sheets.
Large X-ray segmented telescopes will be a key element for future missions aiming to solve still hidden mysteries of the hot and energetic Universe, such as the role of black holes in shaping their surroundings or how and why ordinary matter assembles into galaxies and clusters as it does. The major challenge of these systems is to guarantee a large effective area in combination with large field of view and good angular resolution, while maintaining the mass of the entire system within the geometrical and mass budget posed by space launchers. The slumping technology presents all the technical potentiality to be implemented for the realization of such demanding systems: it is based on the use of thin glass foils, shaped at high temperature in an oven over a suitable mould. Thousands of slumped segments are then aligned and assembled together into the optical payload. An exercise on the mass production approach has been conducted at Max Planck Institute for Extraterrestrial Physics (MPE) to show that the slumping technology can be a valuable approach for the realization of future X-ray telescopes also from a point of view of industrialization. For the analysis, a possible design for the ATHENA mission telescope was taken as reference.
The Hot and Energetic Universe will be the focus of future ESA missions: in late 2013 the theme was selected for the second large-class mission in the Cosmic Vision science program. Fundamental questions on how and why ordinary matter assemble into galaxies and clusters, and how black holes grow and influence their surroundings can be addressed with an advanced X-ray observatory. The currently proposed ATHENA mission presents all the potentiality to answer the outstanding questions. It is based on the heritage of XMM-Newton and on the previous studies for IXO mission. The scientific payload will require state of the art instrumentations. In particular, the baseline for the X-ray optical system, delivering a combination of large area, high angular resolution, and large field of view, is the Silicon Pore Optics technology (SPO) developed by ESA in conjunction with the Cosine Measurement Systems. The slumping technology is also under development for the manufacturing of future X-ray telescopes: for several years the Max Planck Institute for Extraterrestrial physics (MPE) has been involved in the analysis of the indirect slumping approach, which foresees the manufacturing of segmented X-ray shells by shaping thin glass foils at high temperatures over concave moulds so to avoid any contact of the optical surface with other materials during the process, preserving in this way the original X-ray quality of the glass surface. The paper presents an alternative optical design for ATHENA based on the use of thin glass mirror segments obtained through slumping.
MPE is developing modular x-ray mirrors for the next generation of high-energy astronomy missions. The mirror segments are based on thermally formed (a.k.a. slumped) glass sheets, with a typical thickness of 400µm. One of the major challenges is the alignment and integration of the mirror segments and the associated metrology. The optical performance of the mirror can be significantly compromised by adhesive shrinkage, gravity sag or residual stresses influenced by the properties of the mirror mounting and the integration procedure. In parallel with classic coordinate measurement techniques we utilize a deflectometry based metrology system to characterization shape errors of the mirror surfaces. A typical deflectometry setup uses a TFT display to project a sinusoidal pattern onto a specular test surface (SUT) and a camera that observes the reflected image. This reflected image contains slope information of the SUT in the form of distortions of the original displayed pattern. A phase shifting technique can be used to recover this slope information with only very few exposures and reasonable computational effort. The deflectometry system enables us to characterize bonding interfaces of slumped glass mirrors, as well as influence of temporary mounting points, handling and thermal distortions. It is also well suited to measure transient effects.
The μROSI (Micro Roentgen Satellite Instrument) miniature X-ray telescope is the first X-ray telescope specifically designed for an amateur micro satellite. Its mission is to perform an all-sky survey in the soft X-ray band on board the Italian satellite Max-Valier. Due to the limitations imposed by the small size of the spacecraft, the instrument features a silicon drift detector (SDD) with very low power consumption and a focusing optics that consists of 12 nested mirror shells. With a field of view of 1°, μROSI will perform an all-sky survey flying in sun-synchronous orbit (SSO). As a secondary mission objective, the telescope will observe the Earth's upper atmosphere during the all-sky survey, potentially detecting the O2 absorption line.
This paper describes the overall telescope design and gives an overview of the key components of the telescope: the mirror subsystem and the detector subsystem. All subsystems have been tested with flight-like engineering models. The results of these tests are presented in this paper.
The silicon drift detector (SDD) of the μROSI telescope has been tested with a breadboard electronics and the engineering model of the electronics is currently being manufactured. The breadboard test proved that the SDD together with the specifically developed electronics is capable of measuring high resolution spectra in the soft X-ray bandwidth.
One demonstrator mirror shell has been produced and tested in the PANTER X-ray test facility to verify
the X-ray properties. The measurements suggest that the final μROSI mirror system fulfills all requirements for conducting its mission successfully.
Large modular optics made of thousands of mirror segments are a cornerstone of future x-ray mission concepts. In this project we focus on the integration and alignment of slumped glass wolter-1 segments into a mirror module. The two key issues of concern are the handling of a mirror segment during assembly, and the technology to permanently integrate the mirror segments with the supporting mirror module. Both steps can introduce significant shape error to the mirror. Our approach is based on the principle of minimizing distortions to the mirror by using a gravity compliand alignment setup and optimized interfaces. This paper is focused on basic requirements and recent integration experiments, of which analysis and results will be shown and future development discussed.
Future X-ray telescopes need to combine large collecting area with good angular resolution. In order to achieve these aims within the mass limit, light-weight materials are needed for mirror production. We are developing a technology based on indirect hot slumping of thin glass segments; this method enables the production of the parabolic and hyperbolic part of the Wolter type I mirrors in one piece. Currently we use a combination of a porous ceramic for the slumping mould and the glass type D263 for the mirror material. In this study we use glasses that have been polished on one side to remove thickness variations in the glass, in order to investigate their influence on the results. We describe the experimental set-up, the slumping process and the metrology methods. Finally we present the results of an X-ray test of several integrated glass sheets, and give an outlook on future activities.
One of the most challenging tasks for future X-ray observatories is the enhancement of collecting area combined with
very good angular resolution. Light-weight mirror materials, such as thin glass sheets, are needed to achieve this aims
within the mass limits. We are developing a technology based on indirect hot slumping of thin glass segments. This
technique enables us to produce the parabolic and hyperbolic part of the Wolter type I mirrors in one piece. Currently we
focus on a combination of a ceramic slumping mould and glass type D263. The experimental set-up in our laboratories as
well as the slumping process are described in detail; furthermore we report on the metrology methods used for measuring
the glass sheets and moulds. Finally the results of the X-ray tests of several integrated glass sheets are presented.