Details of a programme to investigate the outgassing rate of additively manufactured (AM) aluminium alloys are presented. AM has significant potential benefits to applications in ground- and space-based instrumentation, particularly in mass optimisation, part consolidation and increased design freedom. However, its use in high-risk projects is often curtailed by lack of heritage and an imperfect understanding of the materials. The programme goal was to address one of the most significant topics preventing wider adoption of AM technology in cryogenic and space-based applications; uncertainty about material outgassing. The sensitivity of outgassing rates to various key parameters was characterised, including print method, post-processing and geometrical complexity. Correlation of outgassing rates against other measurable properties, such as sample porosity and surface roughness, was also investigated via the use of X-ray computed tomography and profilometry. Finally, the test apparatus, experimental design and implications of the findings on design and process control are discussed.
The MOONS (Multiple-Object Optical and Near-infrared Spectrograph) is a fibre-fed spectrograph for the European Southern Observatory’s Very Large Telescope. It will provide simultaneous observations of up to 1,000 objects covering the wavelength range 650 nm to 1800 nm. MOONS will also provide an observing mode with 500 object-sky pairs to provide precise sky-subtraction by nodding between object and sky. For this observing mode to be successful the instrument must be well calibrated and the relative throughput of each optical fibre known. The MOONS instrument throughput and wavelength calibration will be characterised, on a daily basis, using the on-board calibration system. The calibration system will illuminate the instrument via a deployable diffuse reflective screen located in front of the focal surface containing the optical fibres. The calibration system provides both spectral calibration via arc lamp illumination, and flat-field illumination via a Digital Micro-mirror Device (DMD) based projector system. This paper will provide a summary of the design and performance of the MOONS calibration system. Flat-field performance results will be presented which demonstrate the calibration unit achieves better than 2% peak to valley illumination uniformity across the 880 mm diameter flat-field screen.
MOONS is a Multi-Object Optical and Near-infrared Spectrograph currently under construction as a third generation instrument for the Very Large Telescope (VLT). It combines the large collecting area offered by the VLT (8.2m diameter), with a large multiplex and wavelength coverage (optical to near-IR: 0.8μm - 1.8μm). Integration of 2 of the arms of the spectrograph (RI and YJ) was recently completed at the UK Astronomy Technology Centre, and initial engineering tests carried out to assess the performance of the spectrograph. This paper presents an overview of the system, the integration and alignment process, and an assessment of the image quality of the two cameras, wavelength coverage and resolving power.
A key technical driver for the MOONS (Multi-object Optical and Near Infrared Spectrograph) instrument is to provide accurate sky subtraction using pairs of adjacent fibres. To achieve this the fibre positioners must achieve extremely close proximity, and the throughput of each fibre must be well characterised. The latter of these conditions requires a calibration system capable of creating a flat field input to the fibres to an illumination uniformity of less than 2% variation. Given the very limited space available in the instrument, a number of systems were considered to achieve this. After consideration of the available options, a novel system using a digital micromirror device (DMD) was selected for implementation. These devices has a long history in commercial displays, and provide a compact, highly responsive, and robust solution to many structured light applications. This paper explains the design and manufacture of the calibration module, as well as the intended test plan for the system.
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