MIRI

The UK’s main contribution to the James Webb Space Telescope is the Mid InfraRed Instrument, better known as MIRI, one of four major scientific instruments on the observatory.

While most instruments on JWST can see from the start of Near-infrared, this infrared camera and spectrometer can see at longer wavelengths, which are difficult or impossible to observe from the ground.

It has three main advantages over other infrared instruments. Firstly, its location in space will remove the background noise effects and interference of the atmosphere which limit ground-based telescopes. Secondly, JWST can be cooled to a very low temperature, reducing the emission from the telescope and greatly improving its sensitivity. Thirdly, the JWST will have a far larger mirror than any other infrared space telescope, giving improved angular resolution.

MIRI was the first instrument to be delivered to NASA in 2012, where it has been built into bigger and bigger subsystems within the observatory. With continuous testing at every stage of integration.

It is an extremely versatile instrument which supports all aspects of the JWST science programme, effectively looking back through time to study the formation of stars and galaxies. MIRI’s camera will also be able to capture spectacular images of the universe.

MIRI is an international project that was designed, built, and tested by a European Consortium of ten member countries, led by the UK in partnership with NASA Jet Propulsion Laboratory. The European contribution is led by Professor Gillian Wright MBE of the UK Astronomy Technology Centre in Edinburgh, the US contribution is led by Dr George Rieke of the University of Arizona.

The UK’s lead role in the instrument involves taking responsibility for the overall science performance, the mechanical, thermal and optical design, along with the assembly, integration, testing and calibration. These roles are shared between the UK institutions in the partnership as follows:

UK Astronomy Technology Centre (UK ATC)

Based at the Royal Observatory in Edinburgh, and operated by Science and Technology Facilities Council (STFC), UK ATC is a national centre of excellence for the development of scientific instrumentation and facilities for ground- and space-based astronomy. It has a world class reputation for delivering innovative and capable cameras, spectrometers and telescope systems. Overall science lead for the instrument; responsible for the overall instrument optical design and providing the spectrometer pre-optic subsystem.

 

STFC RAL Space

Responsible for overall instrument thermal design and analysis and production of all thermal hardware; assembly, integration, testing & verification of instrument including provision of all necessary bespoke test facilities; instrument ground calibration; consortium contamination control leadership role.

University of Leicester

Responsible for instrument overall mechanical design and analysis; provision of instrument primary structure (in partnership with Danish National Space Centre); provision of mechanical ground support equipment.

 

EADS Astrium

Overall project management and engineering leadership role; systems engineering; overall instrument product assurance leadership.

Technical Details

MIRI is the only instrument on Webb covering mid-infrared. Operating between wavelengths of 5 to 28 microns, which, unlike visible light, can penetrate the dense dust clouds which surround newly forming stars and planets. It also features a unique cryogenic cooling system which cools the instrument down to its optimal operating temperature of -266°C to ensure infrared heat from the observatory does not interfere or drown out the instrument’s readings.

The major subsystems of the instrument were designed built and tested at various institutes across Europe:

The Spectrometer Pre-Optics (SPO)
Provided by the UK Astronomy Technology Council in Edinburgh. This is the first unit of the spectrometer which houses the image slicer that splits the incoming light into its component wavelengths. This allows scientists to examine the chemical composition of gas clouds, stars and even planetary atmospheres. The SPO includes two dichroic and grating wheel mechanisms (provided by MPIA, Heidelberg, Germany) which are used to select which part of the incoming light the spectrometer measure.

 

The Spectrometer Main Optics (SMOs)
Provided by Astron, Netherlands. There are two of these units, one takes the shorter wavelength range light from the spectrometer (5 – 12 microns) and the other takes the longer wavelength (12 – 28 microns) light and focuses it correctly onto the detectors.

The Input Optics and Calibration Unit (IOC)
Provided by Centre Spatial Liege (CSL) in Belgium. This unit takes the light from the telescope and divides and correctly formats the beam for the Imager and Spectrometer subsystems. It also contains a Contamination Control Cover mechanism (provided by the Paul Scherrer Institute (PSI) in Switzerland) which ensures the sensitive optical surface stay clean throughout the mission.

The Mid-Infrared Imager (MIRIM)
Provided by CEA, Saclay, France. This is the camera for the instrument which will produce the imagery data. This unit contains an 18 position filter wheel mechanism (provided by MPIA, Heidelberg, Germany) in order to allow images to be captured at different wavelength ranges. This unit also houses a coronagraph which is used to block out the bright light sources so that nearby dim objects can be seen. This will be used to observe the areas around stars so that the much dimmer planets and dust clouds can be studied without the light from the main star blinding the instrument.

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