MOONS (Multi-Object Optical and near-Infrared Spectrograph) will be a fibre-fed, optical to near-infrared multi-object spectrograph designed to utilise the full 25 arcminute diameter field-of-view of the Very Large Telescope and provide a multiplex capability of over 1000 fibres. The baseline design includes a single focal plate and fibre positioning subsystem, consisting of 1000 small dual radial arm modules, which are used to place each fibre, in the exact x, y and z position in the telescope focal plane. Each fibre has a microlens to focus the beam into the fibre at a relatively fast focal ratio of F/3.65 to reduce the Focal Ratio Degradation (FRD). The light is then fed through the fibres to two identical, cryogenic triple arm spectrographs, mounted on the instrument platform. In each spectrograph, the light from 512 fibres, arranged in a pseudo-slit, is split by dichroic filters into three channels (RI, YJ and H) and dispersed on to 4k x 4k detectors in each channel. At the slit there are 32 slitlets, each containing 16 fibres, which feed the collimator. They have been co-aligned to minimise the tilt.
MOONS is the Multi-Object Optical and Near-IR Spectrograph to be mounted at a Nasmyth focus at the Very Large Telescope. The instrument is equipped with 1000 fibres configured over a field of view of ~500 square arcmin using theta-phi fibre positioning units (FPUs). The MOONS metrology system must accurately determine the position of the fibres in the focal plate, providing fast feedback to the instrument control software during operations. The returned fibre positions can be used for calibrations of the FPUs or fast system recovery after a power loss. If required, the system can also be used for calculating fine adjustments of the fibre positions during acquisition. In this paper, a description of the system design, implementation, and testing in the MOONS focal plate are provided. The presented system has high potential for adaptation to a variety of astronomical instrument applications during integration, testing, and operation stages.
Spectroscopy is a primary tool of ground-based and space-borne astronomy. It yields unique astrophysical insights across all contemporary astronomy, from mapping the chemical composition and radial velocities of stars in the Milky Way and nearby galaxies, to accurate redshifts and studies of the physical properties of distant galaxies (internal motions, stellar populations, outflows, etc) over cosmic time. Multi-object spectroscopic surveys have become an essential tool to measure such properties across sufficiently large volumes to draw statistically significant conclusions. A key challenge in the design and construction of MOS instruments is the fibre positioning system. Here we present a new concept for a telescopic fibre positioner (the Edinburgh Telescopic Fibre Positioner: ETFP) in either a theta-r or theta-phi-r configuration. The positioner concept, being developed at UKATC, builds up from the technology of VLT-MOONS and VLT-KMOS and aims to provide a fast field reconfiguration, close packing for high-density targeting, and reliable fibre allocation to maximise the efficiency of observations for future multi-object spectrograph (MOS) facilities.
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.
MOONS (Multi-Object Optical and Near-infrared Spectrograph) is a third-generation visible and near-infrared spectrograph for the ESO Very Large Telescope, currently nearing the end of the assembly phase. The three channel spectrograph is fed via a fibre positioning module (FPM) which configures the location of 1001 fibres. The robotic fibre positioning units (FPUs) have been jointly developed by the UK Astronomy Technology Centre (UKATC) and MPS Microsystems (MPS) and provide a high-performance multiplexed focal plane with excellent transmission characteristics. An overview of the as-built mechanisms and supporting infrastructure is presented, with details on the extensive calibration process carried out. The integration process to date will be described, including a discussion of key lessons learned.
The MOONS multi-object spectrograph relies on an array of 1000 fibre positioners to acquire targets in the focal plane. The fibre positioners have a larger overlap than similar instruments because MOONS can observe in the infrared. The large overlap gives MOONS the ability to acquire close pairs of object and sky targets, but it makes moving positioners to their targets without a collision even more technically challenging. We describe how the MOONS fibre positioner control system overcomes those challenges with custom electronics to manage the synchronisation between the positioners, a collision protection system, and a grid driver software system which manages the control of the fibre positioners. We also describe our experiments with different path planning algorithms and present the latest results from MOONS testing.
The Multi Object Optical and Near-infrared Spectrograph (MOONS) instrument is the next generation multi-object spectrograph for the Very Large Telescope (VLT). The instrument combines the high multiplexing capability offered by 1000 optical fibres deployed by individual robotic positioners with a novel spectrograph able to provide both low- and high-resolution spectroscopy simultaneously across the wavelength range 0.64μm - 1.8μm. Powered by the collecting area of the 8-m VLT, MOONS will provide the astronomical community with a world-leading facility able to serve a wide range of Galactic, Extragalactic and Cosmological studies. This paper provides an updated overview of the instrument and its construction progress, reporting on the ongoing integration phase.
MOONS will be the next Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope, able to simultaneously observe 1000 targets, feeding a set of optical fibres which can be placed at user-specified locations on the Nasmyth focal plane using individual robotic positioners. The sub-fields thus selected are then driven by the fibres into two identical cryogenic spectrographs mounted on the Nasmyth platform of one of the ESO VLT 8 m telescopes. The instrument will provide both medium and high-resolution spectral coverage across the wavelength range of 0.65 μm to 1.8 μm. In this paper we will describe the manufacturing, integration and tests of the two components that interface with the telescope: the MOONS Field Corrector (FC) and the Rotating Front End (RFE) Assemblies. The FC optics will correct the off-axis aberrations of the telescope, as well as determining the shape of the focal surface and the pupil location. The RFE assembly consists of a rotating part, which will be mounted on the VLT Nasmyth Rotator, and be connected to the two static Spectrographs via fibre assemblies, and all the sub-assemblies that give support to the fibre positioning, metrology and calibration units.
KEYWORDS: Spectrographs, Stars, Chemical elements, Ultraviolet radiation, Telescopes, Galactic astronomy, Sensors, Astronomy, Signal to noise ratio, Near ultraviolet
In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (> 40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R >20, 000 (with a lower-resolution, sky-limited mode of R ~7, 000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028.
MOONS (Multi-Object Optical and near-Infrared Spectrograph) will be a fibre-fed, optical to near-infrared multi-objet spectrograph designed to utilise the full 25 arcminute diameter field-of-view of the Very Large Telescope and with a multiplex capability of over 1000 fibres. The baseline design includes a single focal plate and fibre positioning subsystem, consisting of up 1024 small dual radial arm modules, which are used to place each fibre, in the exact x, y and z position in the telescope focal plane. Each fibre has a microlens to focus the beam into the fibre at a relatively fast focal ratio of F/3.65 to reduce the Focal Ratio Degradation (FRD). The light is then fed through the fibres to two identical, cryogenic triple arm spectrographs, mounted on the instrument platform. In each spectrograph, the light from 512 fibres, arranged in a pseudo-slit, is split by dichroic filters into three channels (RI, YJ and H) and dispersed on to 4k x 4k detectors in each channel.
The Multi-Object Optical and near-Infrared Spectrograph (MOONS) will exploit the full 500 square arcmin field of view offered by the Nasmyth focus of the Very Large Telescope and will be equipped with two identical triple arm cryogenic spectrographs covering the wavelength range 0.64μm-1.8μm, with a multiplex capability of over 1000 fibres. Each spectrograph will produce spectra for 500 targets simultaneously, each with its own dedicated sky fibre for optimal sky subtraction. The system will have both a medium resolution (R~4000-6000) mode and a high resolution (R~20000) mode. The fibres are used to pick off each sub field of 1” and are used to transport the light from the instrument focal plane to the two spectrographs. Each fibre has a microlens to focus the beam into the fibre at a relative fast focal ratio of F/3.65 to reduce the Focal Ratio Degradation (FRD). This paper describes the final characteristics and performances of the MOONS fibre link, and their installation status into the slit of the spectrograph during the integration phase in Europe.
MOONS will be the next Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope, able to simultaneously observe 1000 targets, feeding a set of optical fibres which can be placed at user-specified locations on the Nasmyth focal plane using individual robotic positioners. The sub-fields thus selected are then driven by the fibres into two identical cryogenic spectrographs mounted on the Nasmyth platform of one of the ESO VLT 8 m telescopes. The instrument will provide both medium and high-resolution spectral coverage across the wavelength range of 0.65 μm to 1.8 μm. In this paper we will describe the two components that interface with the telescope: the MOONS Field Corrector (FC) and the Rotating Front End (RFE) Assemblies. The FC optics will correct the off-axis aberrations of the telescope, as well as determining the shape of the focal surface and the pupil location. The RFE assembly consists of a rotating part, which will be mounted on the VLT Nasmyth Rotator, and be connected to the two static Spectrographs via fibre assemblies, and all the sub-systems that give support to the fibre positioning, metrology and calibration units.
MOONS (Multi-Object Optical and Near-infrared Spectrograph) is a third-generation visible and near-infrared spectrograph for the ESO Very Large Telescope currently under construction. The instrument’s spectroscopic capabilities are multiplexed via a fibre positioning module (FPM) which configures the location of 1001 fibres. The fibre positioning units (FPUs) have been jointly developed by the UK Astronomy Technology Centre (UKATC) and MPS Microsystems (MPS) to optimise instrument efficiency by providing excellent transmission and an open-loop positioning strategy, allowing a tightly packed focal plane to be rapidly reconfigured. The mechanism geometry enables all positions in the focal plane to be observed in conjunction with a companion sky fibre at close separation. A description of the as manufactured design and production process of the FPUs is presented, along with a discussion of the performance proven to date, including achievement of the critical pupil alignment and positional repeatability requirements. An overview of the custom testing rig built to automate the characterisation and calibration process is also presented.
After completion of its final-design review last year, it is full steam ahead for the construction of the MOONS instrument - the next generation multi-object spectrograph for the VLT. This remarkable instrument will combine for the first time: the 8 m collecting power of the VLT, 1000 optical fibres with individual robotic positioners and both medium- and high-resolution spectral coverage acreoss the wavelength range 0.65μm - 1.8 μm. Such a facility will allow a veritable host of Galactic, Extragalactic and Cosmological questions to be addressed. In this paper we will report on the current status of the instrument, details of the early testing of key components and the major milestones towards its delivery to the telescope.
KEYWORDS: Mirrors, Polishing, Surface roughness, Additive manufacturing, Finite element methods, Space mirrors, Aluminum, Single point diamond turning, Lightweight mirrors, Error analysis, 3D printing
Additive manufacturing (AM), more commonly known as 3D printing, is a commercially established technology for rapid prototyping and fabrication of bespoke intricate parts. To date, research quality mirror prototypes are being trialled using additive manufacturing, where a high quality reflective surface is created in a post-processing step. One advantage of additive manufacturing for mirror fabrication is the ease to lightweight the structure: the design is no longer confined by traditional machining (mill, drill and lathe) and optimised/innovative structures can be used. The end applications of lightweight AM mirrors are broad; the motivation behind this research is low mass mirrors for space-based astronomical or Earth Observation imaging. An example of a potential application could be within nano-satellites, where volume and mass limits are critical. The research presented in this paper highlights the early stage experimental development in AM mirrors and the future innovative designs which could be applied using AM.
The surface roughness on a diamond-turned AM aluminium (AlSi10Mg) mirror is presented which demonstrates the ability to achieve an average roughness of ~3.6nm root mean square (RMS) measured over a 3 x 3 grid. A Fourier transform of the roughness data is shown which deconvolves the roughness into contributions from the diamond-turning tooling and the AM build layers. In addition, two nickel phosphorus (NiP) coated AlSi10Mg AM mirrors are compared in terms of surface form error; one mirror has a generic sandwich lightweight design at 44% the mass of a solid equivalent, prior to coating and the second mirror was lightweighted further using the finite element analysis tool topology optimisation. The surface form error indicates an improvement in peak-to-valley (PV) from 323nm to 204nm and in RMS from 83nm to 31nm for the generic and optimised lightweighting respectively while demonstrating a weight reduction between the samples of 18%. The paper concludes with a discussion of the breadth of AM design that could be applied to mirror lightweighting in the future, in particular, topology optimisation, tessellating polyhedrons and Voronoi cells are presented.
This paper investigates the potential role of small satellites, specifically those often referred to as CubeSats, in the future of infrared astronomy. Whilst CubeSats are seen as excellent (and inexpensive) ways to demonstrate and improve the readiness of critical (space) technologies of the future they also potentially have a role in solving key astrophysical problems. The pros and cons of such small platforms are considered and evaluated with emphasis on the technological limitations and how these might be improved. Three case studies are presented for applications in the IR region. One of the main challenges of operating in the IR is that the detector invariably needs to be cooled. This is a significant undertaking requiring additional platform volume and power and is one of the major areas of discussion in this paper. Whilst the small aperture on a CubeSat inevitably has limitations both in terms of sensitivity and angular resolution when compared to large ground-based and space-borne telescopes, the prospect of having distributed arrays of tens (perhaps hundreds) of IR-optimised CubeSats in the future offers enormous potential. Finally, we summarise the key technology developments needed to realise the case study missions in the form of a roadmap.
Future X-ray astronomy missions require light-weight thin shells to provide large collecting areas within the weight limits of launch vehicles, whilst still delivering angular resolutions close to that of Chandra (0.5 arc seconds). Additive manufacturing (AM), also known as 3D printing, is a well-established technology with the ability to construct or ‘print’ intricate support structures, which can be both integral and light-weight, and is therefore a candidate technique for producing shells for space-based X-ray telescopes. The work described here is a feasibility study into this technology for precision X-ray optics for astronomy and has been sponsored by the UK Space Agency’s National Space Technology Programme. The goal of the project is to use a series of test samples to trial different materials and processes with the aim of developing a viable path for the production of an X-ray reflecting prototype for astronomical applications. The initial design of an AM prototype X-ray shell is presented with ray-trace modelling and analysis of the X-ray performance. The polishing process may cause print-through from the light-weight support structure on to the reflecting surface. Investigations in to the effect of the print-through on the X-ray performance of the shell are also presented.
Additive manufacturing, more commonly known as 3D printing, has become a commercially established technology for rapid prototyping and the fabrication of bespoke intricate parts. Optical components, such as mirrors and lenses, are now being fabricated via additive manufacturing, where the printed substrate is polished in a post-processing step. One application of additively manufactured optics could be within the astronomical X-ray community, where there is a growing need to demonstrate thin, lightweight, high precision optics for a beyond Chandra style mission. This paper will follow a proof-of-concept investigation, sponsored by the UK Space Agency’s National Space Technology Programme, into the feasibility of applying additive manufacturing in the production of thin, lightweight, precision X-ray optics for astronomy. One of the benefits of additive manufacturing is the ability to construct intricate lightweighting, which can be optimised to minimise weight while ensuring rigidity. This concept of optimised lightweighting will be applied to a series of polished additively manufactured test samples and experimental data from these samples, including an assessment of the optical quality and the magnitude of any print-through, will be presented. In addition, the finite element analysis optimisations of the lightweighting development will be discussed.
The Multi-Object Optical and Near-infrared Spectrograph (MOONS) will cover the Very Large Telescope's (VLT) field of view with 1000 fibres. The fibres will be mounted on fibre positioning units (FPU) implemented as two-DOF robot arms to ensure a homogeneous coverage of the 500 square arcmin field of view. To accurately and fast determine the position of the 1000 fibres a metrology system has been designed. This paper presents the hardware and software design and performance of the metrology system. The metrology system is based on the analysis of images taken by a circular array of 12 cameras located close to the VLTs derotator ring around the Nasmyth focus. The system includes 24 individually adjustable lamps. The fibre positions are measured through dedicated metrology targets mounted on top of the FPUs and fiducial markers connected to the FPU support plate which are imaged at the same time. A flexible pipeline based on VLT standards is used to process the images. The position accuracy was determined to ~5 μm in the central region of the images. Including the outer regions the overall positioning accuracy is ~25 μm. The MOONS metrology system is fully set up with a working prototype. The results in parts of the images are already excellent. By using upcoming hardware and improving the calibration it is expected to fulfil the accuracy requirement over the complete field of view for all metrology cameras.
The Multi-Object Optical and Near-Infrared Spectrograph (MOONS) will exploit the full 500 square arcmin field of view offered by the Nasmyth focus of the Very Large Telescope and will be equipped with two identical triple arm cryogenic spectrographs covering the wavelength range 0.64μm-1.8μm, with a multiplex capability of over 1000 fibres. This can be configured to produce spectra for chosen targets and have close proximity sky subtraction if required. The system will have both a medium resolution (R~4000-6000) mode and a high resolution (R~20000) mode. The fibre positioning units are used to position each fibre independently in order to pick off each sub field of 1.0” within a circular patrol area of ~85” on sky (50mm physical diameter). The nominal physical separation between FPUs is 25mm allowing a 100% overlap in coverage between adjacent units. The design of the fibre positioning units allows parallel and rapid reconfiguration between observations. The kinematic geometry is such that pupil alignment is maintained over the patrol area. This paper presents the design of the Fibre Positioning Units at the preliminary design review and the results of verification testing of the advanced prototypes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.