The Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope, scheduled for launch in 2013, will provide a
variety of observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution
spectroscopy. One filter wheel and two dichroic-grating wheel mechanisms allow to configure the instrument between
the different observing modes and wavelength ranges. The main requirements for the three mechanisms with up to 18
positions on the wheel include: (1) reliable operation at T ~ 7 K, (2) optical precision, (3) low power dissipation, (4)
high vibration capability, (5) functionality at 6 K < T < 300 K and (6) long lifetime (5-10 years). To meet these stringent
requirement, a space-proven mechanism design based on the European ISO mission and consisting of a central bearing
carrying the optical wheels, a central torque motor for wheel actuation, a ratchet system for precise and powerless
positioning and a magnetoresistive position sensor has been selected. We present here the detailed design of the flight
models and report results from the extensive component qualification.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. The Spectrometer Main Optics (SMO) system has been designed on the basis of
a 'no adjustments' philosophy. This means that the optical alignment precision depends strongly on the design, tolerance
analysis and detailed knowledge of the manufacturing process. Because in principle no corrections are possible after
assembly, continuous tracking of the alignment performance during the design and manufacturing phases is important.
This is done by controlling the "alignment budget" which allows a detailed comparison of the required and achieved
alignment from component to system level. This paper will describe the development of the SMO alignment budget, and
how it is used to bring the alignment performance under control. In addition, we will discuss the results of the actual
alignment measurements on the SMO hardware and the feedback of these results into the alignment budget.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. In March 2007 the qualification and verification phase of the Spectrometer Main
Optics (SMO), part of the MIRI spectrometer came to an end. In this phase it is shown that the SMO subsystem can
provide the necessary performance and withstand the harsh environments of a launch and outer space. In this phase
different models of the SMO have been inspected with respect to performance parameters like alignment and image
quality and have been exposed to vibration tests and successive cryogenic cool downs. This paper will describe the
philosophy behind the verification plan, the chosen test strategy and reports the results of these tests. In addition the
paper covers the design of the optical test setup, focusing on the simulation of the optical interfaces of the SMO.
Since the start of the design efforts in 2003, the design of the Optical Bench Assembly for MIRI is detailed and finalized. MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the mid infrared under development for the James Webb Space Telescope. MIRI is developed by a combined European-US Consortium. As part of this consortium, ASTRON develops the Spectrometer Main Optics Working in such a large international
consortium requires focus on traceability of requirements, design, interface and verification data. This is achieved using
several systems engineering practices like requirement analyses and allocation, technical performance management and configuration management. These processes are tailored to the complexity and scale of the project. The paper summarizes these practices and provides examples of the tailoring process and system engineering tools used.
In December 2004 the European Consortium that develops the optical bench assembly for MIRI successfully passed the Preliminary Design Review. MIRI is the combined imager and integral field spectrometer for the 5-28 micron wavelength range under development for the JWST. After this PDR milestone the optical design of the MIRI spectrometer is now implemented in a compact, modular mechanical design that puts all optical elements in place within the required tolerances. Many aspects of this design are based on the heritage of previous instruments developed at ASTRON, in particular the cryogenic optics for the mid-IR VLT instruments VISIR and MIDI, but several adjustments
to this design philosophy were made to develop the necessary space-qualified light-weighted components. Prototyping of these components has now started. This paper describes trade-offs and solutions for the opto-mechanical design of the optics (gratings, mirrors and their mountings) and of the main structure of the spectrometer, taking into account optical performance, manufacturability, cost and lead times. It also addresses the complex interface management in a large international consortium and reports first prototype results.
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