MIRI Being prepared for Testing

The James Webb Space Telescope (JWST) was originally commissioned by NASA in the mid-to-late 90s as the replacement for the Hubble telescope, one of the most well know and successful space science missions ever undertaken. Hubble has become a household name, its amazing images seen across the globe inspiring minds both young and old to take an interest in our universe. Hubble has also done some truly groundbreaking science like the imaging of super-novas, discovering a super-massive black hole, and discovering that planetary nebulae (like snowflakes) are never the same twice. So NASA decided that they’d need a replacement to carry on the flagship science once Hubble reaches the end of it's useful life.

One of the main components of a space observatory, such as Hubble or JWST, is the primary mirror. This sets how much light can be collected and condensed down to fall on the instruments. JWST will have a 6.5m primary mirror - over 4 times bigger than Hubble's which will make JWST many times more sensitive and more powerful to look at the very faint and very far distant objects in the universe.

Scale Model of JWST and the JWST Team

Hubble Deep Field Image

Hubble is working mostly in the visible spectrum but also has some instruments working in near infra-red; the part of the infra-red region that is closest to visible light, and also instruments in the near ultra-violet region.

 
Because of the results that Hubble (and ground based observatories) have generated since Hubble was designed it is clear that large amounts of scientific knowledge can be gained from more detailed observations in the infra-red part of the spectrum. For this reason JWST has been designed to operate exclusively in the infra-red part of the spectrum. Infra-red radiation is given off both by relatively cold objects, things that aren’t as hot as stars and so not emitting light in the visible spectrum, but also by things that are very far away. We can only see these far away objects with infra-red because of an effect called red shift, these objects are retreating from us because the universe is expanding, and the light from them is shifting to the red part of the spectrum. This red shift (or Doppler shift) is similar to the effect that you hear when a police car or ambulance is coming towards you and the sound gets higher, and then as it passes you and it moves away the tone drops.

• The first light.

These are the first galaxies and the first stars that were formed after the big bang. Because the universe has since been constantly expanding these objects are now the very furthest objects away from us in the universe and are also moving away at the fastest rate. This means that what would have been visible light light given off by these object has been red shifted so that the wavelengths are very long when they are received at the Earth, so to detect them we have to look a long way into the infra-red.

• How galaxies form

Here the aim is to look into regions in the far distance where new galaxies are just beginning to form. JWST wants to see how the different types of galaxies we can see (spiral, barred, loose clusters etc.) form and what role the differences in conditions during the early years of their formation play in determining the eventual form of a galaxy.

Artists Impression of JWST deep field image

Artists impression of JWST

• Star formation

Stars generally form in regions with a high density of dust and gas. One of the main problems in trying to observe star formation is that the dust that surrounds the young stars is opaque in the visible part of the spectrum. However the infra-red light that is given off by the heat of the star forming passes through the dust due to its longer wavelengths, therefore by observing in the infrared we can see what is happening inside the clouds of dust and gas around the stars.

• Planets around other stars

To trace the origins of the Earth and life in the Universe, scientists need to study planet formation and evolution, including the material around stars where planets form. A key issue is to understand how the building blocks of planets are assembled. Scientists do not know if all planets in a planetary system form in place or travel inwards after forming in the outer reaches of the system. The sensitive instruments on JWST will be able to obtain infra-red images of giant planets and planetary systems and measure their ages and masses.

In addition to studying planets outside our solar system, scientists want to learn more about our own home. Studying the chemical and physical history of the small and large bodies that came together to form the Earth may help us discover how life developed on Earth. JWST will be powerful enough to identify and characterize comets and other icy bodies in the outermost reaches of our solar system, which might contain clues to our origins on Earth.

There will be four instruments on board JWST:

The Near Infra-Red Camera (NIRCam) which is being developed in the USA by a team lead from the University of Arizona and including Lockheed Martin.

The Near Infra-Red Spectrometer (NIRSpec) which is being built under contract to ESA by EADS Astrium in Friedrichshafen, Germany.

The Mid Infra-Red Instrument (MIRI) which is being provided by a consortium of 10 European Countries lead by the UK in partnership with the NASA Jet Propulsion Laboratory and the Goddard Space Flight Centre.

The Fine Guidance Sensor (FGS) is being developed and built by the Canadian Space Agency (CSA). Its main purpose is to allow the satellite observatory to point very accurately at the targets that the scientists wish to observe.

MIRI in the AIV Facility

MIRI being prepared for vibration testing

MIRI

The MIRI is being designed, built, and tested by a European Consortium of 10 member countries led by the UK in partnership with NASA Jet Propulsion Laboratory. The European contribution is led by Dr 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 (UKATC), Edinburgh – overall science lead for the instrument; responsible for the overall instrument optical design and providing the spectrometer pre-optic subsystem.

• Rutherford Appleton Laboratory (RAL), Oxfordshire – 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.

The major subsystems of the instrument are designed built and testing at the various institutes across Europe and the United States. These major subsystems are delivered to RAL where they are put together to form a complete science instrument. These major subsystems are:

• 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 (provides by the Paul Scierrer Institute (PSI) in Switzerland) which ensure 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 i 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.

• The Spectrometer Pre-Optics (SPO) – provided by the UKATC. This is the first unit of the spectrometer which splits the incoming light into it s component wavelengths. This allows scientist 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 will look at.

• 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.

MIRI structural model

• The Focal Plane Modules, Harnesses and Electronics (FPS) – provided by NASA JPL. This is the system that consists of the detectors and the electrical cables and electronics necessary to operate them. These are the ultra-sensitive eyes of MIRI which produce the data which is then beamed to the ground for the science team to study and turn into images.

• The Primary Structure consisting of a CFRP Hexapod (provided by the Danish National Space Centre) and an Aluminium alloy structural Deck (provided by the University of Leicester). This subsystem supports all of the others in the correct position relative to one another (accurate to approximately 1/50th of a millimetre), and relative to the telescope. It must be strong and stiff enough to support the 100kg instrument through the vibration of launch, but also thermally isolate the cold instrument from it s warmer surroundings .

• The Instrument Control Electronics (ICE) – provided by CSL, Belgium. This electronics box controls all of the instrument mechanisms and temperature sensors, and provides housekeeping data necessary to operate and monitor the instrument.

• The instrument control h harnesses – provided by PSI, Switzerland. These electrical cables connect the room temperature ICE to the cryogenic temperature mechanisms and sensors in the instrument while limiting the amount of heat energy conducted to the cold instrument.

• The Thermal Control Hardware (THW) – provided by RAL, UK. The thermal control hardware consists of the cryogenic multilayer insulation (MLI) blankets which insulate the cold instrument from its warmer environment, plus the thermal straps which link the detectors to the dedicated Cryocooler (provided by Northrop Grummen Space Technology, Redondo Beach, California).

After MIRI has been built here at RAL it has to be tested to make sure it can survive the vibrations of the rocket launch and operate successfully in the cold vacuum of space. These tests require a whole series of dedicated and bespoke test facilities to be built for it... To do this we’ve constructed a specific test facility that will operate inside of our main thermal vacuum chamber. This test facility can be cooled, by a set of mechanical cryo-coolers, down to 40 Kelvin to simulate the environment that the instrument will see once in space. These coolers will also cool MIRI itself down even further to its 6.7K (-266.5ºC) operating temperature. MIRI operates at this temperature because infra-red radiation is equivalent to heat therefore any objects warmer than 15.5K (-258ºC) in or around the instrument would give off an infra-red glow that could be detected by the instrument and interpreted as a light signal.

In orbit the JWST is required to have all of the primary mirror and all four instrument at a temperature below 40K (MIRI is even colder than this). To get the temperature to be so cold, JWST has a large, many-layered sun shield that is perhaps the most striking feature of its appearance – it is the size of a tennis court!

What is happening at the moment?

Currently the verification (the second of two prototypes being built before the real flight model) has completed assembly and is about to begin cryogenic vacuum testing. After testing this prototype we will then go on to start building the flight model. Bits of flight model hardware are already in construction at various places around Europe and they’ll start arriving at RAL in the middle of 2008, there is then approximately 18 months of build and test activity to put the instrument together, check that it all works and carry out all the calibration activities to make sure that it is understood how all of the bits interact and that it’s all working as planned. The flight model will then be delivered to the NASA Goddard Space Flight Centre near Washington DC in early 2010. MIRI will then be integrated into the JWST spacecraft which is thoroughly tested before launch which is currently due in the second half of 2013.

The European Consortium working on MIRI consists of

Astron, Netherlands Foundation for Research in Astronomy
CEA Service d'Astrophysique, Saclay, France
Centre Spatial de Liege, Belgium
Consejo Superior de Investigaciones Cient�ficas, Spain
Danish Space Research Institute
Dublin Institute for Advanced Studies, Ireland
EADS Astrium, Ltd., UK
Institute d'Astrophysique Spatiale, France
Instituto Nacional de Tecnica Aerospacial, Spain
Institute of Astronomy, Zurich, Switzerland
Laboratoire d'Astrophysique de Marseille (LAM), France
Max-Planck-Insitut fur Astronomie (MPIA), Heidelberg, Germany
Observatoire de Paris, France
Observatory of Geneva, Switzerland
Paul Scherrer Institut, Switzerland
Physikalishes Institut, Bern, Switzerland
Rutherford Appleton Laboratory (RAL), UK
Toegepast-Natuurwetenschappelijk Ondeszoek (TNO-TPD), Netherlands
UK Astronomy Technology Centre (UK-ATC)
University College, London, UK
University of Amsterdam, Netherlands
University of Cardiff, UK
University of Cologne, Germany
University of Groningen, Netherlands
University of Leicester, UK
University of Leiden, Netherlands
University of Leuven, Belgium
University of Stockholm, Sweden

Other useful links:
http://www.jwst.nasa.gov/
http://www.esa.int/esaSC/120370_index_0_m.html
http://en.wikipedia.org/wiki/JWST
http://www.roe.ac.uk/ukatc/consortium/miri/index.html