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The WFI instrument had its System Requirements Review in 2022, after which the Athena mission underwent a design-to-cost exercise to reduce the estimated Cost-at-Completion to restart the mission with a Delta Phase A-B from 2024. In the meantime, the WFI design has continued its development, including the verification of the most critical aspects to improve the maturity of the technologies used. This paper presents WFI's preliminary design based on its structural, thermal, and functional requirements. It includes the results of the numerical and experimental activities aiming at design verification and demonstration of technology readiness.
The DEPFET sensors operate at temperatures between 193 K and 213 K, dissipating less than 1 W per LD. In contrast, the frontend electronics operate at a higher temperature, requiring approximately 10 W per large detector. The proximity of the ASICs and the DEPFET sensor for electrical performance necessitates a complex thermal design, decoupling the cooling chains for the DEPFET and the FEE.
This paper describes the characterization of the FAME system (freeform active mirror experiment). The system consists of a thin hydroformed face sheet that is produced to be close to the required surface shape, a highly controllable active array that provides support and the ability to set local curvature of the optical surface and the actuator layout with control electronics that drives the active array.
A detailed characterisation of the fully-assembled freeform mirror was carried out with the physical and optical properties determined by coordinate measurements (CMM), laser scanning, spherometry and Fizeau interferometry. The numerical model of the mirror was refined to match the as-built features and to predict the performance more accurately.
Each of the 18 actuators was tested individually and the results allow the generation of look-up tables providing the force on the mirror for each actuator setting. The actuators were modelled with finite element analysis and compared to the detailed measurements to develop a closed-loop system simulation. After assembling the actuators in an array, the mirror surface was measured again using interferometry. The influence functions and Eigen-modes were also determined by interferometry and compared to the FEA results.
The focal plane mask wheel sits in the input focus of the cryostat. It provides 16 user-selectable positions for masks (28x40 mm) used in observation. The key driver for this mechanism is the high repeatability (±2.5 μm) required, equivalent to ~1mas in the input focal plane. The IAC has previously designed, manufactured, tested and put in operation cryogenic wheels with high repeatability; however, the challenge of obtaining a wheel with such repeatability requires testing new concepts of detent positioning systems.
The shutter allows for exposures shorter than the minimum read time of the near-IR detectors and is needed for any CCD observations with the visible cameras. A dual shutter design is needed to achieve the necessary open/close times (<20 ms), but this also provides some redundancy and a graceful failure mode for this critical device. To mitigate risks on the proper behaviour of a fast cryogenics shutter a prototype based on a simple concept has been manufactured. We present the design and results for the performed cryogenic tests of a mask wheel and a shutter prototypes that we have developed.
Once the system architecture has been developed it can be partitioned into a hierarchical product breakdown structure consisting of sub-systems, modules, assemblies, sub-assemblies, and components. Thereafter the product breakdowns structure can be partitioned into a logical work breakdown structure. By using the knowledge and understanding of the development workflows for each of the engineering disciplines required, a single product and work breakdown structure can be used to develop a robust project schedule. In addition, we will show how the processes of configuration management (CMII) are used to integrate the work elements of the various engineering disciplines into a coherent project plan to finalise the designs of parts, modules, assemblies, sub-systems or systems to a level where these parts can either be made or procured for further assembly and integration. Using project planning software such as Microsoft Project, the general shape and critical path of the project can be determined.
Typically, the development of ground based and space astronomical facilities are stretched over many years, even decades. Therefore it is easy to waste a lot of time during the early development phases of the project on nugatory and non-essential tasks. We have adopted the Agile software development methodology to prepare, execute and monitor short term plans (sprints) to ensure progress is being made and that all work elements contributes to the end goal of the project.
We illustrate how these novel techniques have and still are being used in the development of the HARMONI Integral Field Spectrograph. HARMONI was selected as one of the Extremely Large Telescope (ELT) first light instruments. The ELT will be the European Southern Observatory’s (ESO) next generation telescope and observatory and will be built in Chile on Cerra Armazones. The instrument completed its preliminary design phase and the team is now detailing the designs as part of the detailed design phase of the project.
A major objective of this paper is also to show that one single structure, namely the product breakdown structure, is all that is required to plan the development, construction, verification and validation, installation and commissioning of any scientific product. By associating the engineering artefacts required to either procure or build each of the components a robust project time-line can be develop by creating integrated work flows covering all the tasks required to progress the system from conception to a working instrument on sky.
In this context, performance prediction tools can be very helpful during the concept phase of a project to help selecting the best design solution. In the first section of this paper we present the development of such a prediction tool that can be used by the system engineer to determine the overall performance of the system and to evaluate the impact on the science based on the proposed design. This tool can also be used in "what-if" design analysis to assess the impact on the overall performance of the system based on the simulated numbers calculated by the automated system performance prediction tool. Having such a tool available from the beginning of a project can allow firstly for a faster turn-around between the design engineers and the systems engineer and secondly, between the systems engineer and the instrument scientist. Following the first section we described the process for constructing a performance estimator tool, followed by describing three projects in which such a tool has been utilised to illustrate how such a tool have been used in astronomy projects. The three use-cases are; EAGLE, one of the European Extremely Large Telescope (E-ELT) Multi-Object Spectrograph (MOS) instruments that was studied from 2007 to 2009, the Multi-Object Optical and Near-Infrared Spectrograph (MOONS) for the European Southern Observatory’s Very Large Telescope (VLT), currently under development and SST-GATE.
This paper shares one aspect of the experience gained on the SKA project. It explores some of the recommended and pragmatic approaches developed, to get the maximum value from the modeling activity while designing the Telescope Manager for the SKA. While it is too early to provide specific measures of success, certain areas are proving to be the most helpful and offering significant potential over the lifetime of the project.
The experience described here has been on the 'Cameo Systems Modeler' tool-set, supporting a SysML based System Engineering approach; however the concepts and ideas covered would potentially be of value to any large project considering a Model based approach to their Systems Engineering.
We show, in addition to the expected PSF degradation with the field direction, that the PSF retains a coherent core even at large off-axis distances. We demonstrated the large performance improvement of fine tuning the sampling frequency for dimer natural guide stars and an improvement of approx. 50% in SR can be reached above the nominal case. We show that using a smaller AO system with only 20x20 sub-apertures it is possible to further increase performance and maintain equivalent performance even for large off-axis angles.
The FAME design consists of a pre-formed, deformable thin mirror sheet with an active support system. The thin face sheet provides a close to final surface shape with very high surface quality. The active array provides the support, and through actuation, the control to achieve final surface shape accuracy.
In this paper the development path, trade-offs and demonstrator design of the FAME active array is presented. The key step in the development process of the active array is the design of the mechanical structure and especially the optimization of the actuation node positions, where the actuator force is transmitted to the thin mirror sheet. This is crucial for the final performance of the mirror where the aim is to achieve an accurate surface shape, with low residual (high order) errors using the minimum number of actuators. These activities are based on the coupling of optical and mechanical engineering, using analytical and numerical methods, which results in an active array with optimized node positions and surface shape.
A 3D printed version of the actuator is currently being used at the ATC to deform a mirror but it has several advantages that may make it suitable to other applications. The actuator is cheap to produce whilst obtaining a high accuracy and repeatability. The actuator design would be suitable for applications requiring large numbers of actuators with high precision.
We describe the optimisation of the laser inscription process parameters enhancing grating performances via the combination of spectrally resolved grating transmission measurements and theoretical analysis models. The first order diffraction efficiency of the gratings was measured at mid-infrared wavelengths (3-5 μm), and found to exceed 60% at the Littrow blaze wavelength, compared to a substrate external transmittance of 67%. This impressive result implies the diffraction efficiency should exceed 90% for a grating substrate treated with an anti-reflection coating. There is excellent agreement between the modelled grating efficiency and the measured data, and from a least squares fit to the measured data the refractive index modulation achieved during the inscription process is inferred. These encouraging initial results demonstrate that ultrafast laser inscription of chalcogenide glass may provide a potential new and alternative technology for the manufacture of astronomical diffraction gratings for use at near-infrared and mid-infrared wavelengths.
Due to the opening of a new parameter space in optical design, Freeform Optics are a revolution in imaging systems for a broad range of applications from high tech cameras to astronomy, via earth observation systems, drones and defense. Freeform mirrors are defined by a non-rotational symmetry of the surface shape, and the fact that the surface shape cannot be simply described by conicoids extensions, or off-axis conicoids. An extreme freeform surface is a significantly challenging optical surface, especially for UV/VIS/NIR diffraction limited instruments.
The aim of the FAME effort is to use an extreme freeform mirror with standard optics in order to propose an integrated system solution for use in future instruments. The work done so far concentrated on identification of compact, fast, widefield optical designs working in the visible, with diffraction limited performance; optimization of the number of required actuators and their layout; the design of an active array to manipulate the face sheet, as well as the actuator design.
In this paper we present the status of the demonstrator development, with focus on the different building blocks: an extreme freeform thin face sheet, the active array, a highly controllable thermal actuator array, and the metrology and control system.
This course provides a novel functioned-based systems engineering methodology for the design of astronomical instruments and control systems architectures. The primary goal of this course is to provide a framework and a well-proven recipe to develop robust system architectures based on the functional requirements of the system.
The course will be exercise-driven, and the participants will design the system architecture of an instrument during the course. During the course, we will illustrate how the proposed system architecture can meet the science requirements and objectives as well as how the system architecture drives the technical performance requirements.
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