J. Sykes

The Mid-Infrared Instrument for the James Webb Space Telescope, II: Design and Build

The Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) provides measurements over the wavelength range 5 to 28.5 μm. MIRI has, within a single ‘package’, four key scientific functions: photometric imaging, coronagraphy, single-source low-spectral resolving power (R ∼ 100) spectroscopy, and medium-resolving power (R ∼ 1500 to 3500) integral field spectroscopy. An associated cooler system maintains MIRI at its operating temperature of <6.7 K. This paper describes the driving principles behind the design of MIRI, the primary design parameters, and their realisation in terms of the ‘as-built’ instrument. It also describes the test programme that led to delivery of the tested and calibrated Flight Model to NASA in 2012, and the confirmation after delivery of the key interface requirements.

Inauguration and First Light of the GCT-M Prototype for the Cherenkov Telescope Array

The Gamma-ray Cherenkov Telescope (GCT) is a candidate for the Small Size Telescopes (SSTs) of the Cherenkov Telescope Array (CTA). Its purpose is to extend the sensitivity of CTA to gamma-ray energies reaching 300 TeV. Its dual-mirror optical design and curved focal plane enables the use of a compact camera of 0.4 m diameter, while achieving a field of view of above 8 degrees. Through the use of the digitising TARGET ASICs, the Cherenkov flash is sampled once per nanosecond contin-uously and then digitised when triggering conditions are met within the analogue outputs of the photosensors. Entire waveforms (typically covering 96 ns) for all 2048 pixels are then stored for analysis, allowing for a broad spectrum of investigations to be performed on the data. Two prototypes of the GCT camera are under development, with differing photosensors: Multi-Anode Photomultipliers (MAPMs) and Silicon Photomultipliers (SiPMs). During November 2015, the GCT MAPM (GCT-M) prototype camera was integrated onto the GCT stru...

SMILE: a joint ESA/CAS mission to investigate the interaction between the solar wind and Earth's magnetosphere

The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is a collaborative science mission between ESA and the Chinese Academy of Sciences (CAS). SMILE is a novel self-standing mission to observe the coupling of the solar wind and Earths magnetosphere via X-Ray imaging of the solar wind -- magnetosphere interaction zones, UV imaging of global auroral distributions and simultaneous in-situ solar wind, magnetosheath plasma and magnetic field measurements. The SMILE mission proposal was submitted by a consortium of European, Chinese and Canadian scientists following a joint call for mission by ESA and CAS. It was formally selected by ESAs Science Programme Committee (SPC) as an element of the ESA Science Program in November 2015, with the goal of a launch at the end of 2021. In order to achieve its scientific objectives, the SMILE payload will comprise four instruments: the Soft X-ray Imager (SXI), which will spectrally map the Earths magnetopause, magnetosheath and magnetospheric cusps; the UltraViolet Imager (UVI), dedicated to imaging the auroral regions; the Light Ion Analyser (LIA) and the MAGnetometer (MAG), which will establish the solar wind properties simultaneously with the imaging instruments. We report on the status of the mission and payload developments and the findings of a design study carried out in parallel at the concurrent design facilities (CDF) of ESA and CAS in October/November 2015.

The Gamma-ray Cherenkov Telescope for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a forthcoming ground-based observatory for very-high-energy gamma rays. CTA will consist of two arrays of imaging atmospheric Cherenkov telescopes in the Northern and Southern hemispheres, and will combine telescopes of different types to achieve unprecedented performance and energy coverage. The Gamma-ray Cherenkov Telescope (GCT) is one of the small-sized telescopes proposed for CTA to explore the energy range from a few TeV to hundreds of TeV with a field of view ≳ 8° and angular resolution of a few arcminutes. The GCT design features dual-mirror Schwarzschild-Couder optics and a compact camera based on densely-pixelated photodetectors as well as custom electronics. In this contribution we provide an overview of the GCT project with focus on prototype development and testing that is currently ongoing. We present results obtained during the first on-telescope campaign in late 2015 at the Observatoire de Paris-Meudon, during which we recorded the first Cherenkov ima...

High-precision cryogenic wheel mechanisms of the JWST/MIRI instrument: Performance of the flight models

The Mid Infrared Instrument (MIRI) aboard JWST is equipped with one filter wheel and two dichroic-grating wheel mechanisms to reconfigure the instrument between observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution spectroscopy. Key requirements for the three mechanisms with up to 18 optical elements on the wheel include: (1) reliable operation at T = 7 K, (2) high positional accuracy of 4 arcsec, (3) low power dissipation, (4) high vibration capability, (5) functionality at 7 K < T < 300 K and (6) long lifetime (5-10 years). To meet these requirements a space-proven wheel concept consisting of a central MoS2-lubricated integrated ball bearing, a central torque motor for actuation, a ratchet system with monolithic CuBe flexural pivots for precise and powerless positioning and a magnetoresistive position sensor has been implemented. We report here the final performance and lessons-learnt from the successful acceptance test program of the MIRI wheel mechanism flight models. The mechanisms have been meanwhile integrated into the flight model of the MIRI instrument, ready for launch in 2014 by an Ariane 5 rocket.

Fibre Bragg gratings as an alignment aid in JWST MIRI

Largely thermal considerations have led the James Webb Space Telescope (JWST) Mid Infra Red Instrument (MIRI) European Consortium to specify a CFRP hexapod with rigidised Invar endfittings and brackets to form the Primary Structure of the instrument. Each bracket incorporates a pair of orthogonal flexures to provide kinematic mounting to JWST. The principal alignment of the instrument, namely the placing of the Pick-off Mirror (POM) in the telescope frame, must be known and be trackable by a combination of measurement and prediction. Contributors to the alignment are many and various, but potentially great uncertainty lies with the use of a hexapod with field separable joints. In order to provide continuous measurement of the response of the Primary Structure hexapod to integration, g release effects and thermoelastic effects, we have installed a strain gauge array in proximity to the flexures. In this way, asymmetrical strains, inadvertantly introduced during integration, may be detected. The technology employed is that of optical Fibre Bragg Gratings (FBGs), which allow us to measure strains continuously from room temperature down to cryogenic temperatures, with a modest investment in temperature calibration. The strain array has been used during the integration and testing of the Structural Thermal Model of the instrument, and some data have been obtained regarding the utility and effectiveness of this technique in diagnosing sources of alignment error buildup. This paper describes the technology employed, the logic behind these measurements and experience with integration and calibration. Analysis, and the results of some tests, both mechanical and thermal, are presented and discussed.

The microchannel x-ray telescope status

We present design status of the Microchannel X-ray Telescope, the focussing X-ray telescope on board the Sino- French SVOM mission dedicated to Gamma-Ray Bursts. Its optical design is based on square micro-pore optics (MPOs) in a Lobster-Eye configuration. The optics will be coupled to a low-noise pnCCD sensitive in the 0.2{10 keV energy range. With an expected point spread function of 4.5 arcmin (FWHM) and an estimated sensitivity adequate to detect all the afterglows of the SVOM GRBs, MXT will be able to provide error boxes smaller than 60 (90% c.l.) arc sec after five minutes of observation.

The Gamma-ray Cherenkov Telescope, an end-to end Schwarzschild-Couder telescope prototype proposed for the Cherenkov Telescope Array

The GCT (Gamma-ray Cherenkov Telescope) is a dual-mirror prototype of Small-Sized-Telescopes proposed for the Cherenkov Telescope Array (CTA) and made by an Australian-Dutch-French-German-Indian-Japanese-UK-US consortium. The integration of this end-to-end telescope was achieved in 2015. On-site tests and measurements of the first Cherenkov images on the night sky began on November 2015. This contribution describes the telescope and plans for the pre-production and a large scale production within CTA.

Space-compatible strain gauges as an integration aid for the James Webb Space Telescope Mid-Infrared Instrument

Space instruments are designed to be highly optimised, mass efficient hardware required to operate in extreme environments. Building and testing is extremely costly, and damage that appears to have no impact on performance at normal ambient conditions can have disastrous implications when in operation. The Mid-Infrared Instrument is one of four instruments to be used on the James Webb Space Telescope which is due for launch in 2018. This telescope will be successor to the Hubble Space Telescope and is the largest space-based astronomy project ever to be conceived. Critical to operation of the Mid-Infrared Instrument is its primary structure, which provides both a stable platform and thermal isolation for the scientific instruments. The primary structure contains strain-absorbing flexures and this article summarises how these have been instrumented with a novel strain gauge system designed to protect the structure from damage. Compatible with space flight requirements, the gauges have been used in both ambient and cryogenic environments and were successfully used to support various tasks including integration to the spacecraft. The article also discusses limitations to using the strain gauge instrumentation and other implications that should be considered if such a system is to be used for similar applications in future.

Management of the JWST MIRI pFM environmental and performance verification test campaign

The Mid-Infrared Instrument (MIRI) is one of four scientific instruments on the James Webb Space Telescope (JWST) observatory, scheduled for launch in 2018. It will provide unique capabilities to probe the distant or deeply dust-enshrouded regions of the Universe, investigating the history of star and planet formation from the earliest universe to the present day. To enable this the instrument optical module must be cooled below 7K, presenting specific challenges for the environmental testing and calibration activities. The assembly, integration and verification (AIV) activities for the proto-flight model (pFM) instrument ran from March 2010 to May 2012 at RAL where the instrument has been put through a full suite of environmental and performance tests with a non-conventional single cryo-test approach. In this paper we present an overview of the testing conducted on the MIRI pFM including ambient alignment testing, vibration testing, gravity release testing, cryogenic performance and calibration testing, functional testing at ambient and operational temperatures, thermal balance tests, and Electro-Magnetic Compatibility (EMC) testing. We discuss how tests were planned and managed to ensure that the whole AIV process remained on schedule and give an insight into the lessons learned from this process. We also show how the process of requirement verification for this complex system was managed and documented. We describe how the risks associated with a single long duration test at operating temperature were controlled so that the complete suite of environmental tests could be used to build up a full picture of instrument compliance.