PROCEEDINGS OF SPIE SPIEDigitalLibrary.org/conference-proceedings-of-spie The Athena x-ray optics development and accommodation Bavdaz, Marcos, Wille, Eric, Ayre, Mark, Ferreira, Ivo, Shortt, Brian, et al. Marcos Bavdaz, Eric Wille, Mark Ayre, Ivo Ferreira, Brian Shortt, Sebastiaan Fransen, Mark Millinger, Maximilien J. Collon, Giuseppe Vacanti, M. Barrière, Boris Landgraf, Mark O. Riekerink, Jeroen Haneveld, Ronald Start, Coen van Baren, Desiree Della Monica Ferreira, Sonny Massahi, Sara Svendsen, Finn Christensen, Michael Krumrey, Evelyn Handick, Vadim Burwitz, Miranda J. Bradshaw, Giovanni Pareschi, Giuseppe Valsecchi, Dervis Vernani, Geeta Kailla, William Mundon, Gavin Phillips, Jakob Schneider, Tapio Korhonen, Alejandro Sanchez, Dominique Heinis, Massimiliano Tordi, Richard Willingale, "The Athena x-ray optics development and accommodation," Proc. SPIE 11852, International Conference on Space Optics — ICSO 2020, 1185220 (11 June 2021); doi: 10.1117/12.2599341 Event: International Conference on Space Optics — ICSO 2021, 2021, Online Only Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use International Conference on Space Optics—ICSO 2020 Virtual Conference 30 March–2 April 2021 Edited by Bruno Cugny, Zoran Sodnik, and Nikos Karafolas The Athena x-ray optics development and accommodation International Conference on Space Optics — ICSO 2020, edited by Bruno Cugny, Zoran Sodnik, Nikos Karafolas, Proc. of SPIE Vol. 11852, 1185220 · © 2021 ESA and CNES CCC code: 0277-786X/21/$21 · doi: 10.1117/12.2599341 Proc. of SPIE Vol. 11852 1185220-1 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 The ATHENA X-ray Optics Development and Accommodation Marcos Bavdaz1, Eric Wille1, Mark Ayre1, Ivo Ferreira 1, Brian Shortt1, Sebastiaan Fransen1, Mark Millinger1, Maximilien J. Collon2, Giuseppe Vacanti2, Nicolas M. Barrière2, Boris Landgraf2, Mark Olde Riekerink3, Jeroen Haneveld3, Ronald Start3, Coen van Baren4, Desiree Della Monica Ferreira 5, Sonny Massahi5, Sara Svendsen5, Finn Christensen5, Michael Krumrey6, Evelyn Handick6, Vadim Burwitz7, Miranda Bradshaw7, Giovanni Pareschi8, Giuseppe Valsecchi9, Dervis Vernani9, Geeta Kailla11, William Mundon11, Gavin Phillips11, Jakob Schneider12, Tapio Korhonen13, Alejandro Sanchez14, Dominique Heinis14, Massimiliano Tordi15, Richard Willingale 16 1 European Space Agency, ESTEC, Keplerlaan 1, PO Box 299, NL-2200 AG Noordwijk, The Netherlands 2 cosine, Oosteinde 36, NL-2361 HE Warmond, The Netherlands 3 Micronit Microfluidics B.V., Colosseum 15, NL-7521 PV Enschede, The Netherlands 4 SRON, Sorbonnelaan 2, NL-3584 CA Utrecht, The Netherlands 5 DTU Space, Elektrovej 328, 2800 Kgs Lyngby, Denmark 6 Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, D-10587 Berlin, Germany 7 MPI für extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany 8 INAF Osservatorio Astronomico di Brera, Via E. Bianchi 46 I- 23807, Merate (LC), Italy 9 Media Lario S.r.l., Località Pascolo, I-23842 Bosisio Parini (LC), Italy 10 Thales Alenia Space Switzerland Ltd, Schaffhauserstrasse 580, 8052 Zürich, Switzerland 11 Teledyne E2V, 106 Waterhouse Lane, Chelmsford, Essex CM1 2QU, England 12 Fraunhofer Institute for Material and Beam Technology, Winterbergstrasse 28, D-01277 Dresden, Germany 13 Opteon Oy, Väisäläntie 20, FI-21500 Piikkiö, Finland 14 ALBA Synchrotron, Carrer de la Llum 2-26, 08290, Cerdanyola del Vallès, Barcelona, Spain 15 EIE Space Technologies Srl, Via Torino 151/A - 30172 Mestre-Venezia, Italy 16 University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom ABSTRACT The ATHENA mission, under study and preparation by ESA as its second Large-class science mis sio n, req u ires t h e largest X-ray optics ever flown, building on a novel optics technology based on mono crystalline silicon. Referred t o as Silicon Pore Optics technology (SPO), the optics is highly modular and benefits from technology s pin-in from the semiconductor industry. The telescope aperture of about 2.5 meters is populated by 600 mirror modules, accurat ely co - aligned to produce a common focus. The development of the SPO technology is a joint effort by European industrial and research entities, working together to address the challenges to demonstrate the imaging performance, robustness and efficient series production of the ATHENA optics. A technology development plan was established and is being regularly updated t o reflect t h e l at est developments, and is fully funded by the ESA technology development programmes. A n in d ust rial co nso rtiu m was formed to ensure coherence of the individual technology development activities. The SPO technology uses precision machined mirror plates produced using the latest gen eratio n t op q ualit y 12 in ch silicon wafers, which are assembled into rugged stacks. The surfaces of the mirror plates and the integral support structure is such, that no glue is required to join the individual mirror plates. Once accurately aligned with respect to each other, the surfaces of the mirror plates merge in a physical bonding process. The resultant SPO mirror modules are therefore very accurate and stable and can sustain the harsh conditions encountered during launch and are able to tolerate the space environment expected during operations. Proc. of SPIE Vol. 11852 1185220-2 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 The accommodation of the ATHENA telescope is also innovative, relying on a hexapod mechanism to align the optics to the selected detector instruments located in the focal plane. System studies are complemented by dedicated t echnolo gy development activities to demonstrate the capabilities before the adoption of the ATHENA mission. Keywords: X-ray optics, X-ray astronomy, ATHENA, Silicon Pore Optics, X-ray telescopes, X-ray testing, Technology preparation 1. NOVEL OPTICS FOR THE NEXT GENERATION X-RAY SPACE TELESCOPE ATHENA (Advanced Telescope for High-ENergy Astrophysics) [1] is the second Large Clas s ESA Scien ce mis s io n selected for flight in the early 2030s, aiming at studying the hot and energetic Universe at X-ray energies. With its ambitious science goals it poses very demanding requirements on the X-ray optics and the payload detector instru ments [2, 3]. No X-ray optics technology flown to date can satisfy the needs of ATHENA. Some X-ray optics are lig h t en oug h an d could achieve the large effective area, but would not be able to achieve the required angular resolution. Other technologies achieve excellent angular resolution, but would require thick mirrors, resulting in prohibitive mass. Figure 1: AT HENA require a radically new optics technology. It is interesting to note, that the X-ray optics flown to da t e sh o w a correlation between the resolving power achieved (i.e. the number of angular resolution elements provided pe r arc minute) and the required area density (i.e. the effective area provided per kg of optics). T his correlation extends over the different types o f X - r a y optics technologies used: (1) foil based optics (light blue: as used e.g. for HIT OMI [4], or slumped glass, as for NuST AR [5]), (2 ) replicated optics (light grey, e.g. NEWT ON [6]), and (3) monolithic optics (yellow, e.g. CHANDRA [7]). AT HENA requires ver y large optics (about 2.5 m diameter) with a low mass, and at the same time it has to provide a good angular resolution (see green diamond). Effectively the AT HENA optics technology has to be as light as foil optics, but perform like the monolithic optics. T he Silicon Pore Optics (SPO) technology delivers the required performance for AT HENA: the blue diam ond in the graph indicated the performance demonstrated today. T he SPO technology is being further improved to match the AT HENA needs. Proc. of SPIE Vol. 11852 1185220-3 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 Figure 1 illustrates the challenge. Plotting the effective area provided per mass unit (cm2/kg) as function of t h e ang ular resolution expressed as angular resolution elements per arc minute, the X-ray missions flown to date show a clear correlation. Missions like HITOMI [4], relying on foil based optics, or on slumped glass like NuSTAR [5], missions like NEWTON [6] using replicated optics, and missions like CHANDRA [7] relying on monolithic optics all follow this correlation line, despite being so different in terms of X-ray optics technology. Nature is telling us a message here. ATHENA requires an unprecedented combination of low mass, large effective area and good an gu lar reso lut io n. A s indicated in figure 1 by a green diamond, these requirements are significantly off the correlation line populated by existing missions. Evidently ATHENA requires a novel type of X-ray optics, which exceed the performance of existing technologies. Silicon Pore Optics (SPO) [8-31] was invented in order to enable missions like ATHENA. With its pore structure it requires the optical elements to span much shorter distances between support points, and therefore achieves to comb in e thin (and therefore low mass) mirrors with good figure accuracy, resulting in good angular resolution. The SPO technology has already demonstrated that it uniquely combines mass efficiency and imaging performan ce in a way no other mission succeeded to date, as indicated by the blue diamond in figure 2. The evolution of the SPO technology is ongoing, moving the blue diamond to the right, with the aim to reach the position of the green diamond b y the time of adoption of the ATHENA mission, expected in 2022. 2. MODULAR SILICON PORE OPTICS In order to make it possible to build the ATHENA X-ray optics, the optics must be modular. Small optical elemen t s are required, since only these can be produced effectively within the schedule and cost constraints. The p ro ductio n o f t h e ATHENA optics has to be automatized as far as possible, to ensure constant quality, fast production and low cost. As shown in figure 2, ATHENA spacecraft on first glace is quite similar to NEWTON or CHANDRA, albeit being larger, with its 12 m focal length. The payload instruments are significantly larger and more complex, requiring elaborate cooling and EMC protection. The optics is substantially larger, with an optical diameter of about 2.5 m. The optics consists of a metallic structure populated by 600 SPO mirror modules and holding metrology equipment inclu din g s tar trackers and alignment tools. Activities have started to demonstrate the production of the complete full size ATHENA Mirror A ssem bly demonstrators (two parallel contracts with the prospective possible ATHENA primes). These will serve to confirm the en v iro n ment al requirements to be imposed onto the SPO mirror modules, and to demonstrate the feasibility to manufacture such a larg e X-ray optics within specifications. The 600 mirror modules must be accurately co-aligned to focus onto the same spot in the focal place. The required A IT (Assembly Integration and Testing) process has been developed [32-34] and demonstrated to exceed the required performance. The SPO mirror modules development started more than a decade ago, and has achieved a high level o f t ech nolo gical readiness. Production equipment is in place to produce thousands of mirror plates and dozens of mirror modules per year. This was made possible by the implementation of robotic equipment and industrial production tools already in the development phase. Proc. of SPIE Vol. 11852 1185220-4 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 Figure 2: T he AT HENA optics is modular, with 600 mirror modules populating its aperture. Silicon Pore Optics (SPO) can be mass produced at a competitive cost, relying on robotic production and mass produced commercial mirror elements. T he SPO mirror modules are robust and compact, each effectively representing a complete imaging X-ray optical unit. A large number of technology development activities were initiated and implemented by ESA, contracting key players in industry and research institutions. Expertise was brought together in focused activities, each having a clear objective an d measurable targets. The cooperative spirit was required within each of the technology development activities, and a close coordination between the many activities was mandatory. A Technology Development Plan (TDP) was elaborated (figure 3) and is kept updated to consider technical and programmatic evolution. All activities are fully funded and led by ESA. The activities cover three areas: (1) the SPO mirror modules including mirror plate production and coatings, (2) the mirror assembly module including the optical bench and the AIT process, and (3) nu merical simulations, study of interaction with particles (mainly protons and micrometeoroids), and the preparation of the required test and verificatio n facilities. All major activities have been started and are progressing in their implementation. The extension of the main SPO mirro r module activity is planned for mid-2021 (dashed red box). The technology development activities will be concluded by the time of the Mission Adoption Review (MAR), expected for 2022. At the MAR the results of the ATHENA system studies [35] and technology activities will undergo a thorough review, in order to establish the readiness of the mission to pass into the implementation phase. Th e feasibilit y o f t h e mission will have to be demonstrated in technical and programmatic aspects. For the optics at MAR the performance will have to have been demonstrated in the relevant environmen t [36], i.e. t h e launch loads and operation in the space environment for the duration of the mission will have to be demonstrated, as well as the compatibility with the schedule, resources (mainly mass), and cost constraints. Proc. of SPIE Vol. 11852 1185220-5 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 Figure 3: A comprehensive technology plan was elaborated and is being evolved and implemented by a consortium of industry and institutions. T he development programme is fully funded and led by the European Space Agency (ESA). T he group of activities indicated in the top of the graph regard the development of the SPO mirror modules, the center cluster of activities ( in dic a t e d in orange) regard the assembly of hundreds of mirror modules into a single optical assembly (the AT HENA Mirror Assembly), and the group of activities indicated in the bottom of the graph complement the development activities, addressing numerical simulations, test facilities and particle effects. The performance of the SPO optics is continuously improving, as shown in figure 4, plotting the angular resolution of the SPO optics over time. The results shown are X-ray measurements of the optics in double reflect io n, meas ured at t h e Physikalisch-Technische Bundesanstalt (PTB) laboratory of the BESSY-II synchrotron facility [37,38]. The primary and secondary stacks are mounted in tandem, as required for the Wolter-I config urat io n. Two cases are shown: the first 10 mirror plate pairs on the left, and the first 20 plate pairs on the right. The percentages indicated in t h e figure refer to the contiguous fraction of the optics width contributing to the value shown . In all cas es t he co mp lete height is measured (i.e. 10 and 20 plates respectively). The potential of the SPO technology is evident from the 10 plate result: 10% of the area is alread y o u t performin g t h e requirement, featuring a 4.2” HEW. The increase of the area fraction with high performance is the target of the o n goin g activities. The complete area, i.e. 100% of the width and measuring all stacked plates shows a HEW of 9.4” HEW. Note that this is already substantially better than the NEWTON optics, but at a much reduced mass and cost per effective area. The further improvement of the angular resolution of the SPO modules is the focus of t h e main o n go ing t ech nolo gy development activity, and several augmentations of the tooling and mirror plates are under work. Proc. of SPIE Vol. 11852 1185220-6 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 It is important to note, that the measured samples were made using largely automated equipment, therefore giv in g v ery repeatable results. The production method will essentially remain the same when moving into the implementation phase, and is not a one-off attempt to produce the best possible mirror module. Figure 4: T he SPO technology is evolving rapidly. T he graphs above show the improvement of the angular resolution (Half Energy Width, HEW) obtained with SPO optics over time. XOUs are X-ray Optical Units consisting of the two required optical elements to provide true imaging (these are the primary and secondary reflectors of a Wolter type I system). Each optical elem en t consist of a stack of co-aligned mirror plates. T he data shown integrates the performance of the lower 10 and 20 plates, respectively, and the percentages indicated refer to the contiguous area fraction measured (i.e the width of the area measured). T hese measurements were performed at the Physikalisch -Technische Bundesanstalt (PT B) laboratory of the BESSY-II fac ilit y in Berlin, in double reflection. Full area performance is already at 9.4” HEW, and smaller areas outperform the required 4.3” HEW. 3. 100.000 MIRRORS, 600 MODULES, ONE MIRROR ASSEMBLY The development of the ATHENA optics is undertaken with a simultaneous development of the tooling and eq uip men t required to manufacture, assemble, integrate, test and verify the optics. This is an essential component of demonstratin g the ATHENA optics technology readiness. The ATHENA telescope with require the production of about 100.000 flight quality mirror plates. The majorit y will b e used in the flight optics, others are required to populate the engineering and qualification mode ls, or will end up as fligh t spares. Considering this large number of mirror plates to be produced, it was seen as mandatory to establish two man u factu res (Micronit in The Netherlands and Teledyne E2V in the United Kingdom) able to produce the required mirror plates. Th e approach being that each single manufacturer should be able to produce the complete set of mirror plates for ATHENA , but expecting to be required to deliver about half. Any potential problems with the mirror plate pro d uctio n d u rin g t h e flight programme are thereby significantly de-risked. Proc. of SPIE Vol. 11852 1185220-7 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 The mirror plates require many steps in their production, employing automated equipment as far as possible. The starting material for the mirror plate production is available on the semiconductor market: high qualit y s ing le cry stal 300 mm diameter wafers, with both sides highly polished to the required X-ray super-polish finish. These surfaces are as s mo oth as required for the bonding operation when stacking the plates. Figure 5 shows some of the equipment used for the mirror plate production. One of the work horses is the dicing machine shown on the bottom right, available at each of the mirror plate ma nufacturers. These machines work autonomously, ingesting pristine wafers and producing the ribbed structure required on the plates, as well as dicing them to the precise dimensions required. One of the large advantages of the SPO technology is the accessibility of the reflective mirror s u rface rig h t u p t o t h e stacking operation. This makes it possible to use elaborate cleaning and coating processes to improve the reflectivity and therefore the effective area of the optics. Figure 5: About 100.000 mirror plates will be required for the implementation of the ATHENA optics (including qualification a n d spare mirrors). T his demands an industrial approach to the production of mirror plates. Currently about 2 .000 mirror plates are already being produced per year, to feed the SPO mirror module and other developments. Industrial equipment as shown on the two bottom left photos is used to manufacture the mirror plates. Coatings can be sputtered onto the SPO mirror plates, an d a r e a n important element contributing to the performance of the AT HENA optics. In the top left a study of different coa t in g o p t io n s is shown. T he coatings are applied using commercial equipment: the machine shown on the bottom left was already installe d a t t h e SPO mirror module manufacturer, cosine, and is able to coat all the required 100.000 mirror plates in the allocated two y e a r s. An Ion Beam Figuring (IBF) machine is currently being procured, and will allow the further improvement of the mirror plates, allowing also for corrections to me made on individual plates. On the top left a snapshot of a coating optimisation study is provided, led by DTU in Denmark, buildin g o f t h eir larg e heritage in making X-ray mirror coatings. Equally important is the ability to reproducibly apply the required coating onto the mirror surfaces, for 10s of thousands of mirror plates, within the short time interval permitted by the mission Proc. of SPIE Vol. 11852 1185220-8 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 implementation schedule. A suitable industrial coating machine, shown on the bottom left o f fig u re 5, was t h erefo re installed at the cosine premises. This single machine has a throughput sufficient to coat all the ATHENA mirror plates in the allotted time. The SPO mirror plates are processed by both plate manufacturers in batches, e.g. in automated wet benches as shown in figure 5 top right, reducing the cost and allowing reference plates to be pulled from the production without much affecting the production yield. This type of equipment has also recently been installed at cosine to remove the lithographic resist, provide additional cleaning, and plate bonding preparation. An Ion Beam Figuring (IBF) machine is being manufactured (it will be a new model allowing automatic p ro cessing o f 300 mm wafers) and will be commissioned at cosine in 2021. This equipment will allow the furt her improvement o f t h e mirror plate figure, and make it possible to produce ‘reset’ mirror plates to minimize stack-up errors. After production and quality acceptance each mirror plate has to me mounted, ensuring it is formed into the right s h ape, and securing its figure for the duration of the mission. Figure 6 shows the robotic stacking machine used to mount the mirror plates (top left). To ensure t h e cleanlin ess an d repeatability of the process, the operation is highly procedural and defined in software routines. The operators are located remotely and control the process form a dedicated control room (top, middle). Figure 6: T he SPO mirror plates are assembled into mirror stacks. T his operation is performed robotically at cosine, ensur in g t h e cleanliness and repeatability required for the operation. Complex equipment is being employed, controlled remotely by operato rs, to very efficiently produce the mirror stacks. T he time required to mount a single mirror plate has been constantly decreasin g, a n d is already adequate for the production of the AT HENA telescope: only about 7 minutes are required to mount a mirror plate! This stacking process is a critical step in the production of the SPO mirror modules and required attention to many details. The process must form each mirror plate into the correct shape, deposit it onto the growing mirro r p lat e s t ack, and ensure that the correct figure is achieved over the complete area. Proc. of SPIE Vol. 11852 1185220-9 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 Despite this complexity, only a few minutes will be available to mount each mirror plate in the flight programme. As shown in figure 6 top right, currently about 7 minutes are required to mount a mirror plate, which is fast enough already. SPO mirror modules are being developed for three radii simultaneously. Indeed fours stackin g robots have been built up, ensuring that all required developments can occur in parallel. In figure 7, at the right, computer renderings of t h e o u ter, middle and inner mirror modules are shown, top to bottom. Lessons learned in one radius are transferred to the others. The mirror modules are tightly packed into the ATHENA Mirror Assembly structure, and require hig h p recis ion wit h tolerances of few microns and arc seconds Figure 7: T he AT HENA Mirror Assembly is populated by 600 carefully co-aligned mirror modules. Currently mirror modules a r e being developed for three representative radii: outer-most, middle and inner-most (right side of the image, top to bottom). A dedicated AIT process had to be developed to ensure the required speed and accuracy can be obtained. T o demonstrate the production of the AT HENA Mirror Assembly structure activities have started with both potential primes for the implementation of AT HENA. 60 degree sectors will be initially produced, following by the complete full size demo nstrator models. The ATHENA Mirror Assembly has to be positioned on the ATHENA spacecraft with respect to the focal plane instruments. Using a hexapod system the Mirror Assembly can be tilted to focus onto one of the two focal plane instruments (figure 8 top right). A prototype of this hexapod has been built and is cu rren tly u nd erg oin g t estin g an d verification (figure 8, bottom right). A second hexapod system is used during the launch sequence. This hexapod system (launch lock) is later releas ed fro m the Mirror Assembly, once in orbit and before commencing in-orbit commissioning and observations. A damping system is required to ensure the optics is sufficiently protected from the mechanical shocks occurring during launch. A prototype of a bipod for such a system is shown in figure 8, on the left. Proc. of SPIE Vol. 11852 1185220-10 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 Figure 8: T he AT HENA focal plane instruments are of such complexity and size, that the classical approach of moving the detectors in and out of the focal position is no longer possible. T herefore it is the optics which has to be moved in orde r t o se le c t the active detector instrument. T he ATHENA Mirror Assembly is therefore mounted on a hexapod, which allows the tilting of t h e optics in the direction of the desired instrument. A further benefit of this solution is the possibility to fine tune the focus and position of the optical axis during operations in orbit. T echnology activities are demonstrating the implementation of the hex a p od (right) and the launch support and damping system (left). 4. DEFINING THE TELESCOPE GEOMETRY FOR FLIGHT The maturation of the optics technologies for ATHENA is running in tandem with the system studies. During 2020 there has been a major effort amongst all stakeholders to define a consistent geometry. This effort result ed in t h e fi rs t v ery detailed and consistent definition of the reference telescope design being agreed by everyo ne wh ich will n o w b ein g assumed for all the developments (from plate level to mirror assembly level). The main parameters of the reference telescope design are the following (see figure 9): - Focal length = 12 m - 487 mm < Optical diameter < 2512 mm - 6 sectors (i.e. Mirror Assembly with 6 fold symmetry – 5 spokes) - 100 MM per sector (total of 600 MMs) - 15 rows - 4 stacks per SPO mirror module (2 primary and 2 secondary in double reflection) - 38 plates per stack (36 of which contributing as effective area) per stack - Reference plate at the middle of the stack (plate 19) - Plate membrane thickness of 110 microns and rib pitch of 2.3 mm - Wolter-Schwarzschild (W-S) geometry, where the kink of each reference plate of each stack follo ws t he W -S sphere (i.e. is placed at a distance of 12-m from the detector) Proc. of SPIE Vol. 11852 1185220-11 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 - Plate length fixed per stack and defined for the optimal grazing angle of the reference plate per stack (result in g in stacks of different length in a MM) - All plates wedged to ensure confocality - Plate widths fixed per MM and optimised per row (ensuring technological limits, accommodation of necessary mirror structure, heaters, dynamic and thermal distortions, etc…) Figure 9: Definition of the AT HENA reference telescope design. T op left: Plate arrangement per stack – 38 plates p e r st a c k ( 3 6 reflective + non-reflective baseplate + non reflective top plate). Top right: Stack arrangement on the aperture. Reference p la t e o f each stack follows the Wolter Schwarzschild sphere (12 -m from the detector), plate length fixed per stack for optimal grazing angle of reference plate leading to different stack lengths along the aperture; each MM has 4 stacks (2 primary and 2 se c o n da r y ) . Bottom: Complete Mirror Assembly with 600 MMs arranged in the 6 identical sectors and 15 rows. The result was the definition of all the geometric parameters of each MM and even each plate which now ensures that all mathematical models from the SPO technology activities are consistent with the Mirror Assembly Module Demonstrator and other system level activities. The new reference telescope design also allowed some performance gains by reducing the amount of MMs (in creasing open area ratio) while guaranteeing that all technological limits, structural and accommodation constraints were still met . This gain was estimated to be 12% for 1 keV and 16% for 7 keV effective areas. 5. ATHENA AIT AND TEST FACILITIES In order to ensure the timely availability of the ATHENA mirror integration facility, the design and constructio n o f t h e AIT facility has already started at the premises of Medialario near Milano, Italy. Figure 10 shows a computer ren derin g of the facility. On the right is the UV Vertical Optical Beam facility (UVOB), extending about 6 m underground and about 17 m above. Proc. of SPIE Vol. 11852 1185220-12 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 The UV collimator system on the bottom consists of a 2.6 m diameter Zerodur mirror, currently in t h e fin al s t ages o f polishing at Opteon in Finland, which will be used to generate a 2.6 m diameter UV beam, collimated to bet t er t h at 1”, pointing exactly vertically (to a fraction of arc second). This UV beam is used to position t he mirro r mo d u les b efo re fixing them to the telescope structure. A person is shown for scale next to the ATHENA Mirror Assembly, preparing the integration o f t h e n ext SPO mirro r module (figure 10, top right). The mirror module integration process itself is remotely controlled, ensurin g cleanlin ess and repeatability. The AIT facility is expected to be completed before the ATHENA MAR. Co-located with the AIT facility is the Vertical X-ray Test Facility VERT-X [39] (figure 10, left). The concept of this facility has been studied in detail and its feasibility demonstrated. The key elements of VERT-X are the X-ray collimated beam source, a system consisting of a micro-focus X-ray source and an Wolter-I mirror, and a positioning system moving this source to cover the complete area of the ATHENA Mirror Assembly. The VERT -X facility allows the horizontal accommodation of the ATHENA Mirror Assembly (i.e. vertical optical axis), minimising gravity induced distortions. Regular X-ray verifications are expected to be conducted during the process of p o pulat ing t he A THENA Mirror Assembly with the 600 SPO mirror modules. Figure 10: T he size of the AT HENA optics requires the development of new AIT and X-ray test facilities. Co-location of these facilities to the extent possible is mandatory, in order to minimize the logistic complexity and cost for the AT HENA implementation. A dedicated AIT facility is being built by Medialario in Italy, which will also accommodate the Vertical X -ray T est Facility VERT -X. As shown on the right, the AIT facility consists of a large UV collimator (2.6 m diameter!) , producing a vertical UV beam which is used to guide the integration of the 600 mirror modules into the AT HENA Mirror Assembly. T he VERT -X facility, shown on the left, will produce a vertical collimated X-ray beam, which will be able to scan the complete area of the AT HENA Mirror Assembly. Key elements of this facility are being implemented already. Proc. of SPIE Vol. 11852 1185220-13 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 The large number of facilities required for the production and verification of the ATHENA o p tics req uires adequate advance planning and implementation. As illustrated in figure 11, next to the A IT and VERT-X facilit ies , o t h er majo r installations will be used in the implementation phase, and all are being currently prepared. The assembly of the SPO mirror modules requires a highly collimated X-ray beam, and two facilities will be av ailab le. BESSY-II (figure 11 top right) in Berlin, Germany, is already in use for the SPO development programme, with two dedicated beamlines being available. Further two beamlines are expected to be implemented after MAR. Since synchrotron facilities are very complex and can incur shut-downs, a further beamline is currently being implemen t ed at the ALBA synchrotron facility (figure 11 bottom left) near Barcelona, Spain . The Panter facility [40] (figure 11 mid left) operated by the Max Plack Gesellschaft near Munich in Germany will continue to be used as a classic test facility with a long beamline of 130 m providing large area sampling. A new type of beamline is being built by the Osservatorio Astronomico di Brera (OAB) near Milano in Italy. This facility, BEaTriX [41] (figure 11 mid right), will provide a collimated X-ray beam of sufficient size to illuminate a complete SPO mirror module, and is intended to be used as a mirror acceptance testing and calibration facility. Figure 11: A large number of facilities are required for implementing the AT HENA telescope optics and to verify it’s performance. T he facilities are located across Europe and consist of synchrotron beamlines required for the assembly of mirro r modules (BESSY-II in Berlin, Germany, and ALBA Synchrotro n near Barcelona, Spain), mirror module acceptance and calibration facilities (Panter near Munich, Germany, and BEaT riX near Milano, Italy), the AIT and VERT -X facilities (near Milano, Italy) with the UV collimator (produced by Opteon in Finland). In addition (not shown) the NASA XRCF facility in Huntville, Alabama, USA, is being prepared for testing the AT HENA optics. Proc. of SPIE Vol. 11852 1185220-14 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 23 Jun 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ICSO 2020 Virtual Conference International Conference on Space Optics 30 March-2 April 2021 6. CONCLUSION ATHENA is the second Large Class Science mission of ESA, and is enabled by a no vel type pf X-ray optics. The Silicon Pore Optics (SPO) technology combines low mass, good angular resolution and large effective area in a way n o o t h er existing X-ray optics technology able to operate in space has achieved to date. The SPO technology is being developed in a holistic approach, addressing the performance and the programmatic (schedule and cost) aspects related to the mass production required for ATHENA , as 600 mirro r mo d u les h av e t o b e produced in about 2 years. A coordinated technology plan is being implemented, being fully funded and led by ESA and involving in d ust rial an d institutional players. Existing expertise, commercial equipment, processes and components are b ein g comb in ed an d brought to fruition to develop and manufacture the largest X-ray optics ever flown in space. Benefiting from immense investments made by the semiconductor industry and spinning in technologies develop ed fo r the ground sector, it became possible to satisfy the needs of ATHENA. The running developments will proceed until t h e ATHENA Mission Adoption Review, currently expected in 2022, and will evolve into the implementation phase, aiming at a launch in the early 2030s. With a modular approach, the ATHENA optics of about 2.5 m in diameter is populated with 600 mirror modules, wh ich have to be accurately aligned. A dedicated integration process was developed and the facility required fo r t h e fu ll s ize ATHENA optics is being implemented. The verification and calibration of the large ATHENA optics poses its own challenges and required new test facilit ies , which are also being developed and implemented. Coordination with existing NASA facilities, in particular the XRCF, is ongoing in addition. ACKNOWLEDGEMENTS The authors would like to express their appreciation for the great collaborative spirit in the joint endeavou r t o d evelo p and produce the optics for the ATHENA mission. REFERENCES [1] K. 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