We present an update to the 2024 Magellan Infrared Multi-Object Spectrograph (MIRMOS). MIRMOS is a wide-field (13′ × 3′) near-infrared (0.89-2.4 μm) spectrograph with either a multiobject or integral-field mode. MIRMOS is designed to perform either faint-object distant-object spectroscopy, or high-signal-to-noise transmission spectroscopy of exoplanet atmosphere. MIRMOS is designed to deliver a spectral resolution of > 3, 400, delivering the Y, J, H, and K bands over four Hawaii H2RG detectors. The slit robot allows the observer to create 92 slits or a 26′′ ×20′′ integral-field unit can be swapped in. In this proceeding, we describe changes since the last SPIE conference.
For the last 35 years at CSEM we've developed compliant systems in optomechatronics; pioneering revolutionary designs for iconic terrestrial and space observation projects, such as the next generation EUMETSAT geostationary satellites: Infrared Atmospheric Sounding Interferometer (IASI) - Meteosat Third Generation (MTG). In astrophysics, we've contributed to major projects including: Stratospheric Observatory for Infrared Astronomy (SOFIA); Multi-Object Spectrometer for InfraRed Exploration for KECK telescope (MOSFIRE). Thanks to flexures, our systems have infinite lifetime and reliability, suffer neither friction nor wear and don't require any lubrication. They're capable of enduring extreme conditions while maintaining high accuracy. We tailor projects to our customers' needs and support scientists in enhancing their state of the art instruments.
For the development of the Focus Mechanism of the CLUPI instrument of the ExoMars 2020 mission, the CSEM implemented a design based on flexible structure technology and the use of Commercial Off-The-Shelf (COTS) components. This choice was essentially motivated by the availability of the miniature sensor and actuator components. Such approach presents many challenges such as:
the qualification of the OTS voice-coil motor and Linear Variable Differential Transformer (LVDT),
the implementation of a reliable launch locking system,
the design of a flexible structure mechanism compatible with harsh mechanical environment.
The present article describes each of the above problematics and the investigation carried by CSEM to find solutions meeting the mission needs and constrains.
The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) achieved first light on the W. M. Keck Observatory’s Keck I telescope on 4 April 2012 and quickly became the most popular Keck I instrument. One of the primary reasons for the instrument’s popularity is that it uses a configurable slitmask unit developed by the Centre Suisse d’Electronique et Microtechnique (CSEM SA) to isolate the light from up to 46 objects simultaneously. In collaboration with the instrument development team and CSEM engineers, the Keck observatory staff present how MOSFIRE is successfully used, and we identify what contributed to routine and trouble free nighttime operations.
A Configurable Slit Unit (CSU) has been developed for the Multi-Object Spectrometer for Infra-Red Exploration
(MOSFIRE) instrument to be installed on the Keck 1 Telescope on Mauna Kea, Hawaii. MOSFIRE will provide NIR
multi-object spectroscopy over a field of view of 6.1' x 6.1'. The reconfigurable mask allows the formation of 46 optical
slits in a 267 x 267 mm2 field of view. The mechanism is an evolution of a former prototype designed by CSEM and
qualified for the European Space Agency (ESA) as a candidate for the slit mask on NIRSpec for the James Webb Space
Telescope (JWST). The CSU is designed to simultaneously displace masking bars across the field-of-view (FOV) to
mask unwanted light. A set of 46 bar pairs are used to form the MOSFIRE focal plane mask. The sides of the bars are
convoluted so that light is prevented from passing between adjacent bars. The slit length is fixed (5.1 mm) but the width
is variable down to 200 μm with a slit positioning accuracy of ± 18 μm. A two-bar prototype mechanism was designed,
manufactured and cryogenically tested to validate the modifications from the JWST prototype. The working principle of
the mechanism is based on an improved "inch-worm" stepping motion of 92 masking bars forming the optical mask.
Original voice coil actuators are used to drive the various clutches. The design makes significant use of flexure
structures.
Multi-object instruments provide an increasing challenge for pick-off technology (the means by which objects are selected in the focal plane and fed to sub-instruments such as integral field spectrographs). We have developed a technology demonstrator for a new pick-off system. The performance requirements for the demonstrator have been driven by the outline requirements for possible ELT instruments and the science requirements based on an ELT science case. The goals for the pick-off include that the system should capable of positioning upwards of one hundred pick-off mirrors to an accuracy better than 5 microns. Additionally, the system should be able to achieve this for a curved focal surface -- in this instance with a radius of curvature of 2m.
This paper presents the first experimental results from one of the approaches adopted within the Smart Focal Plane project -- that of a Planetary Positioning System. This pick-and place system is so called because it uniquely uses a combination of three rotation stages to place a magnetically mounted pick-off mirror at any position and orientation on the focal surface. A fixed angular offset between the two principal rotation stages ensures that the pick-off mirror is always placed precisely perpendicular to the curved focal plane. The pick-off mirror is gripped and released by a planar micromechanical mechanism which is lowered and raised by a coil-actuated linear stage.
A mechanical slit mask mechanism has been designed for the Near Infrared Spectrograph of the James Webb Space Telescope. This mechanism was successfully tested at a cryogenic temperature of 30K, in vacuum. The reconfigurable mask allows to form 24 optical slits in a 137 x 137 mm2 field of view. The slit length is fixed (4.8 mm) and their width can range from 50 μm to 137 mm. The slit positioning accuracy is ± 5 μm and the slit width accuracy is ± 8 μm. The working principle of the mechanism is based on an improved "inch-worm" stepping motion of 48 masking bars forming the optical curtain. Voice coil actuators are used to drive the various clutches and the principal mobile stage. Ratchets which engage in the teeth of a rack machined on the bars allow to cancel the accumulation of motion errors as steps succeed one another. The design makes significant use flexure structures. Cryogenic performance, life and vibration tests have been performed successfully on subassemblies of the mechanism and a full-scale prototype.
NAOS (Nasmyth Adaptive Optics System) is the adaptive optics system presently developed for the ESO VLT. The field selectors are to feed the NAOS wavefront sensor with the light coming from an appropriate reference source which can be up to 1 arcmin (on the sky) distant from the center of the field of view. A large input tip-tilt-piston mirror selects the required part of the field of view. A second active mirror redirects the selected field to the wavefront sensor. The displacement of both mirrors are synchronized. The NAOS Field Selector consists of two extremely accurate tip-tilt-piston mirror mechanisms controlled in closed loop. Each mechanism provides a mechanical angle amplitude of +/- 6 degrees with a resolution and mechanical stability of 0.42 arcsec rms over 20 minutes. This implies a dynamic range of 100,000 which requires an extremely accurate, very high resolution closed loop control. Both mirrors are made in SiC for low mass and inertia. The design configuration of the mechanism in based on three electromagnetic actuators 120 degrees apart with the mobile magnets mounted on flexure guides. The mirror is supported by a combination of flex pivots and a membrane for flexibility in tilt and high radial stiffness. All kinematic joints consist of flexure elements so that the mechanism is essentially frictionless. The control system is implemented on a VME bus operated with the VXWorks OS with high electrical resolution (>= 18-bit) AD and DA interface boards. The controller has been carefully designed to achieve the best overall performances, i.e., a very good noise rejection, and a relatively low settling time.
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