Antonio Scippa

The INAF Astronomical Observatory of Palermo has adapted one of the large vacuum chambers of the X-ray Astronomy Calibration and Testing (XACT) facility for cryogenic interferometric testing of the 1-m-class primary mirror developed for ESA’s Ariel mission. Ariel’s all-aluminum telescope will operate in flight at approximately 55 K. Under the nearly isothermal conditions expected in flight, uniform thermal contraction is expected primarily to change the mirror radius of curvature. In contrast, departures from uniform thermal contraction, for example due to temperature gradients or mechanical boundary conditions, may introduce surface figure deformations under ground-test conditions. The cryogenic campaign was therefore designed to characterize the mirror surface evolution during cooldown and to provide experimental data for the validation and correlation of the thermomechanical and Structural-Thermal-Optical Performance models. The upgraded facility consists of a 2-m-diameter, 3-m-long vacuum chamber with a 1.4-m-diameter access hatch for mirror integration. It is equipped with a closed-loop helium cryocooler, a dedicated radiative and conductive cooling system, a 4D Technology interferometer operating through a fused-silica vacuum window, and an isostatic fork support designed to minimize parasitic mechanical stresses and ensure reproducible boundary conditions. Pre-test thermal modeling predicted that the system could cool the mirror to about 100 K, as expected for the ground test, maintaining temperature gradients of less than 5 K. The paper describes the facility and experimental configuration, the thermal commissioning phase, and the interferometric campaign, which comprised two cryogenic cooldown cycles. The commissioning phase provided an initial assessment of the facility’s thermal performance, whereas the two interferometric cycles demonstrated the measurement chain’s capability to operate under cryogenic test conditions. The resulting thermal and optical dataset provides the experimental basis for model correlation. It supports the future validation of the Structural-Thermal-Optical Performance models of the Ariel primary mirror in preparation for Telescope Assembly verification activities.

We present MICHELANGELO, a single-object, cross-dispersed echelle spectrograph optimised for high-resolution (R ≈ 100,000 in the M band; R ≈ 50,000 in the L band) spectroscopy in the 3-5 μm atmospheric window. Designed to be fed by an adaptive optics system at an 8-10 m class telescope – primarily the Large Binocular Telescope – the instrument targets characterisation of exoplanetary atmospheres via molecular mapping in the fundamental vibrational bands of CO, H2O, CO2, CH4 and SiO. The key enabling technology is a Germanium immersion echelle grating: diffraction occurring inside a substrate with refractive index n ≈ 4.0 reduces the required physical grating size by a factor n and compresses the overall instrument volume by a factor n3 ≈ 64 relative to a conventional air-path design of equivalent resolving power. The resulting cryostat is smaller than 40 cm in diameter and 70 cm in length with a total mass below 100 kg – a reduction of 30-50× compared with CRIRES+. The design contains no cold movable parts and records the entire L or M band simultaneously on a single 4096×4096 HgCdTe detector, providing 3-4× more molecular lines for cross-correlation than any current wavelength setting. Beyond its ground-based mission, the compact architecture is directly applicable to space deployment. We describe the companion MICHELE (Mid-IR Immersion grating Cryogenic Hardware Evaluation for Launch Environment) project, which advances the Technology Readiness Level of the Germanium grating and its kinematic mount from TRL 3-4 to TRL 5-6 through finite-element analysis, vibration qualification, and cryogenic interferometric testing.

In milling, the advancement of CAM strategies has increased the need for tailored algorithms for semi-finished phase computation. In some cases (e.g., thin-wall milling), variable radial engagement of the tool during the toolpath is desired, leading to the need of non-uniform machining allowance on the component that could be achieved only with a non-uniform offset algorithm, i.e., offset where the distance to the initial contour varies along that input. This work presents a general algorithm for non-uniform offset of polyline curves. The approach is based on 2D polygons and Boolean union operation, following these steps: (i) projection segments are generated, (ii) polygons (trapezoids and circular sectors) are created, (iii) Boolean union of all the polygons is performed, (iv) boundary of interest is extracted. The proposed algorithm is able to handle both internal and external offset and is robust for complexity of both the polyline and variable offset magnitude along that line, as proven by several examples and two applications to thin-wall milling provided.

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 purpose of the mission is the study of exoplanetary atmospheres on a target of ∼ 1000 exoplanets. Ariel 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, followed by a hyperbolic secondary, a parabolic collimating tertiary and a flat-folding mirror directing the output beam parallel to the optical bench; all in bare aluminium. The choice of bare aluminium for the realization of the mirrors is dictated by several factors: maximizing the heat exchange, reducing the costs of materials and technological advancement. To date, an aluminium mirror the size of Ariel’s primary has never been made. The greatest challenge is finding a heat treatment procedure that stabilizes the aluminium, particularly the Al6061T651 Laminated alloy. This paper describes the study and testing of the heat treatment procedure developed on aluminium samples of different sizes (from 50mm to 150mm diameter), on 0.7m diameter mirror, and discusses future steps.

Repairing, remanufacturing, and refurbishing high value metal components are crucial to move towards a more sustainable economy. Nowadays, repairing operations on high value parts, such as dies, are generally performed using time-consuming manual approaches that rely on the operator’s expertise. The research idea of this paper is to develop a retrofit kit to provide additive capabilities to an existing milling machine, allowing automatic repairing of components thanks to a fast switch between additive and machining operations without a relevant economic investment such the acquisition of a brand-new machine: the final cost of the solution is lower than 10% with respect to the mean cost of a 5-axis milling machine. The additive technology used in this work is Wire Arc Additive Manufacturing (WAAM) that is characterized by a higher deposition rate and a simpler and cost-effective equipment with respect to other techniques (e.g., laser cladding). The design of the system is illustrated in the paper together with the analysis of the results achieved repairing a test case: a die casting mold made of AISI H13 tool steel.

In 3-axis milling, cutting force analysis represents one of the main methods to increase the quality and productivity of the process. In this context, cutting force shape gives information of both monitoring and prediction of the cutting process. However, the cutting force shape is not unique, and it changes according to the cutting strategy, tool geometry, and cutting parameters. This paper presents a comprehensive approach to predict and classify cutting force shapes in 3-axis milling operations. In detail, the proposed approach starts by classifying the cutting force shapes for a single fluted endmill (i.e., single flute force shape), and, considering how the single flute force shapes may overlap one another, it extends the classification to a general multiple-fluted endmill. Moreover, the method provides, through analytical equations, angles, and magnitude dimensionless parameters of each key point, describing each shape classified. Finally, the proposed approach was experimentally validated through several milling tests in different cutting conditions.