High-precision cryogenic wheel mechanisms for the JWST NIRSpec instrument

Weidlich, Kai; Fischer, M.; Ellenrieder, Marc M.; Gross, T.; Salvignol, Jean-Christophe; Barho, Reiner; Neugebauer, Christian; Königsreiter, G.; Trunz, M.; Müller, Friedrich; Krause, O.

doi:10.1117/12.789663

Cited by 12 publications

(7 citation statements)

References 4 publications

(6 reference statements)

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“…Based on the fact that MoS2 is the most extensively used solid lubricant in space mechanisms, a particularly timely example will be highlighted here: the James Webb Space Telescope (JWST), which is planned for launch in 2021 and is the successor to the Hubble Space Telescope. MoS2 has been determined as the solid lubricant of choice for sensitive mechanisms employed in a number of precision instruments on JWST, including the Near Infrared Spectrograph (NIRSpec) and the Mid Infrared Instrument (MIRI) [50,57]. Critical to the choice of MoS2 as the preferred solid lubricant for these high-precision instruments was the fact that it preserves its lubricative properties down to cryogenic temperatures (which include 30 K, the temperature around which JWST will be operating) [58] and the high uniformity with which it can be deposited on precision bearings employed in the instruments at sub-micron thicknesses, ensuring stable operation.…”

Section: Tribological Applications Of Mos2mentioning

confidence: 99%

Solid Lubrication with MoS2: A Review

et al. 2019

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Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. An effort is made to cover the main theoretical and experimental studies that constitute milestones in our scientific understanding. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.MoS2 belongs to the family of layered two-dimensional transitional metal dichalcogenides (TMDs). Like graphite and hexagonal boron nitride, its crystal structure consists of covalently bonded sheets, which form stacks that are held together only by weak Van der Waals interactions [16]. It occurs naturally as the mineral molybdenite, an important Mo ore. Due to the strong bonding inplane and weak bonding out-of-plane, mechanical and other properties are highly anisotropic [17], and the stacks can be easily sheared. Single-layer or few-layer (i.e. 2D) MoS2 (analogous to graphene) can be produced and studied individually [18].MoS2 has several different possible structures (polytypes), depending on the bonding within the sheets and the stacks of the sheets. While graphite has a single plane of atoms per sheet, in MoS2 each sheet consists a plane of Mo atoms sandwiched between two planes of S atoms. The single-sheet structure can feature trigonal prismatic coordination around Mo, which is the semiconducting 1H ("hexagonal") structure, or octahedral bonding, which is the metallic 1T ("trigonal") phase. 1H and the ideal 1T each have 3 atoms (MoS2) per unit cell ( Figure 1); however, theoretical calculations with density-functional theory (DFT)[19] and X-ray diffraction (XRD) experiments [20] have shown that in fact 1T is unstable with respect to distortions. The most commonly reported structure is a 3× 3 distortion that triples the unit cell, known as the 1T′ phase [21].Each single-sheet structure can be stacked into a crystal where the next sheet is exactly above the preceding one (AA stacking), producing the 1H, 1T, and 1T′ polytypes. The naturally occurring polytypes in molybdenite, however, are only based on the 1H sheet, and show more complicated stacking [9]. The more common is the 2H structure with 2 sheets per cell in AB stacking, where an S atom in one layer is above an Mo atom in the layer below [22,23]. The less common 3R ("rhombohedral") structure has 3 sheets per cell with ABC stacking [22,24]. These structures are shown in Figure 1. Mo-S bond lengths are around 2.4 Å for all polytypes [25]. DFT calculations show only very small energy differences between the 2H and 3R phases [25]. This insensitivity to stacking, and the low surface energy for 2H-MoS2 of 47 mJ/m 2 =...

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Section: Tribological Applications Of Mos2mentioning

confidence: 99%

Solid Lubrication with MoS2: A Review

et al. 2019

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“…1c. A detailed description of the mechanism can be found in a companion publication to this article, 3 as well as in earlier publications. 4, 5…”

Section: The Filter and Grating Wheel Assembliesmentioning

confidence: 98%

The optical components of the NIRSpec wheel mechanisms

Ellenrieder

Weidlich

Nelles

et al. 2008

Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation

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The Near-Infrared Spectrograph (NIRSPEC) on board the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of NIR sub-bands as well as spectral resolutions. Reconfiguration of the NIRSpec instrument will be achieved using a Filter Wheel Mechanism (FWA) which carries 7 transmission filters and one reflective mirror and a Grating Wheel Mechanism (GWA) which carries six gratings and one prism. The dispersive components on the grating wheel (GWA) cooperate with the edge transmission filters mounted on the filter wheel (FWA) which block the higher dispersion orders of the gratings. The paper gives an overview on the design of all optical elements, their key requirements and the employed manufacturing approach. Test results from breadboard and component level qualification phase are also given.

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“…To address that, two magneto-resistive position sensors are used to measure the 'tip and tilt' displacement of the selected GWA element each time the wheel has rotated into place. 13 The calibration of the GWA position sensors aims at finding the relationship between the sensor voltages and the corresponding angular displacement of the wheel, with respect to a reference location, given by the chosen reference point of the spectrograph instrument model. For the dispersers, a number of dedicated exposures are taken with an internal lamp with intermediate wheel movements.…”

Section: Grating Wheel Position Sensormentioning

confidence: 99%

Preparing the NIRSpec/JWST science data calibration: from ground testing to sky

Oliveira¹,

Birkmann²,

Boeker³

et al. 2018

Preprint

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The Near-Infrared Spectrograph (NIRSpec) is one of four instruments aboard the James Webb Space Telescope (JWST). NIRSpec is developed by ESA with AIRBUS Defence & Space as prime contractor. The calibration of its various observing modes is a fundamental step to achieve the mission science goals and provide users with the best quality data from early on in the mission. Extensive testing of NIRSpec on the ground, aided by a detailed model of the instrument, allow us to derive initial corrections for the foreseeable calibrations. We present a snapshot of the current calibration scheme that will be revisited once JWST is in orbit.

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High-precision cryogenic wheel mechanisms for the JWST NIRSpec instrument

Cited by 12 publications

References 4 publications

Solid Lubrication with MoS2: A Review

Solid Lubrication with MoS2: A Review

The optical components of the NIRSpec wheel mechanisms

Preparing the NIRSpec/JWST science data calibration: from ground testing to sky

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