Successor to Hubble
The result of a huge international effort, in which STFC's RAL Space participated, the James Webb Space Telescope (JWST, or “Webb") is expected to be launched in the not-so-distant future. At a location 1.5 million kilometres from Earth, the spacecraft will be able to study the universe in unprecedented detail.
Conceived in 1989 as successor to the Hubble Space Telescope, Webb is set to take over as the world's flagship space observatory. Its 6.5m diameter primary mirror provides more than seven times the collecting area (and therefore sensitivity) of Hubble, meaning that it will be able to directly observe parts of space and time that have never been observed before.
Led by NASA, the Webb project has seen major contributions from Canada and Europe. The European contribution includes the launch, as well as two of the four on-board instruments—one of which is the Mid-InfraRed Instrument (MIRI).
MIRI's sensitive detectors, which capture the longest wavelength of light (5-28 microns), will enable Webb to see distant galaxies, newly forming stars, and faintly visible comets. With both a camera and a spectrograph, this instrument will be able to provide outstanding astrophotography as well as information about the physical details of distant objects.
The instrument was built by a consortium of twelve European countries (led from UK ATC in Edinburgh) and the US, with the assembly and calibration conducted here at the UK's national space laboratory—RAL Space.
RAL Space's contributions began in 2001, two years before our Chief Engineer Paul Eccleston became involved. He explains:
“I was responsible for the team that was building, testing and calibrating the instrument. We were putting together the different pieces that came from our partners around Europe and the United States, testing to make sure it would survive the launch and cold environment of space, and calibrating so that we can really understand what the data is going to mean when it comes back down to us."
The Webb Telescope's Mid Infrared Instrument (MIRI). Credit: STFC RAL Space
Keeping MIRI cool
Key scientific aims for Webb's mission include searching for light from the first stars and galaxies 13.2 billion lights away, looking at how galaxies form, studying the lifecycles of stars, and examining how solar systems are born.
Distant galaxies continue to move even further away from us as the universe expands. As this happens, the wavelength of the light emitted by these galaxies is stretched, shifting to longer—and subsequently redder—parts of the spectrum. This phenomenon means that the light from the very earliest galaxies has been “red-shifted" so far that they are best observed in infrared (IR) wavelengths.
Therefore, to answer fundamental questions about our universe, Webb will reach out into the IR as well as visible light.
This light passes through gas and dust clouds surrounding regions where stars and planets are born, giving us a unique insight into the factors that drive the diversity of planetary systems we see today. To observe the IR radiation given off by these distant or cool objects, Webb must itself be cryogenically cooled. To keep the telescope and instruments below 45K (-228°C), the telescope hides from the Sun and Earth behind a sunshield made of five ultrathin layers of aluminised foils, each one the size of a tennis court but less than 1/20th of a millimetre thick.
MIRI must operate at an even colder temperature of 7K (-266°C) in order to detect the faint signals coming from distant stars and galaxies. Unlike the other instruments on board, MIRI has a dedicated cooler, provided by NASA's Jet Propulsion Lab, and RAL Space thermal engineers continue to play an important role in keeping MIRI cool and making sure it can reach the operating temperatures required.
Origami in Space
The sheer scale of the telescope and sunshield prevents Webb from being launched at its full size. Within two weeks after launch a series of mechanisms will unfold the complex origami puzzle to deploy the spacecraft. With such a complex machine, and no chance of repair after launch, there has been a painstaking and time-consuming process of repeatedly checking everything to make sure all goes to plan. By necessity, this has led to a very long gestation period for the mission to minimise the risk of anything going wrong.
While at RAL Space, MIRI alone underwent 100 days in a thermal vacuum chamber, where it spent 85 days below room temperature to make sure all components would work correctly at the low temperatures needed. MIRI has been tested and checked many more times since it was delivered to NASA in 2012.
The Final Countdown
Thousands of us around the world who have collaborated over the past 20 years excitedly await the final part of Webb's journey from drawing board into fully operational telescope. The results will surely be both fascinating and beautiful as we open a new window to our universe.