How do you design and build the kit you need to do the science you want to do?
Webb is a leap forward on previous missions of this type and has many unique features which make this a mission worthy of its 'flagship' status. Want to know the what/where/why and how? We put our engineering hats on and picked six key things that Webb needs to be a game-changing telescope. To dig a bit deeper, learn more about the Mid-InfraRed Imager (MIRI), one of Webb’s four scientific instruments.
Infrared light is invisible to our eyes but we are familiar with it as the sensation of heat on our skin. It sits just off the red end of the rainbow and is very useful for astronomers. It allows you to peer through obscuring clouds of dust, explore the coolest stars and take pictures of very distant galaxies. The main mirror for Webb is actually coated with gold because it reflects infrared light really well.
An optical/infrared comparison of a region within the Carina Nebula. Image credit: NASA, ESA, M. Livio and the Hubble 20th Anniversary Team (STScI)
Many things in space emit light in the infrared, but so do many things on Earth, including us. To get some of the clearest views, and avoid seeing infrared light from Earths own atmosphere, you've got to get into space. This becomes more important the further into the infrared you wish to go. Low-Earth orbit, where the Hubble Space Telescope currently lives, isn't far enough away from the Earth. Webb will be much more distant, roughly four times further away than the Moon.
Webb will hover around a distant point known to astronomers as 'L2'. A useful staging point for science missions. Image credit: ESA
When it comes to telescopes, bigger, if done right, is usually better. You get two main advantages from having a larger main mirror: you can detect fainter objects and you can see finer detail. To allow it to achieve its lofty goals, Webb will have the largest mirror ever flown in space. A honeycomb of 18 smaller sections, it will be 6.6 metres across in total. This is so big it has to be folded away for launch or it won't fit on the rocket!
Webb's mirror undergoing cryogenic/vacuum testing at NASA Johnson. Image credit: NASA/Chris Gunn
First, the telescope will require protection from the glare of the Sun. Second, and more importantly, the telescope itself will be its own source of infrared light unless it is kept very cold. Solution: Webb sunshield. It will unfold in space and is made up of five layers of very thin reflective material about the size of a tennis court. Shielded from the Sun, the temperature of the telescope will eventually dip to a very chilly -234 degrees Celsius, cold enough for science observations. It will take a couple of months to cool down, even in outer space.
A full-scale test of the five-layer sunshield to be used with Webb. Image credit: NASA/Chris Gunn
Even with the chilly temperatures obtained with the sunshield, the Mid-infrared Instrument (MIRI) is still too toasty. It sees further into the infrared than the other instruments on board and will be able to detect its own infrared emission at those temperatures. Imagine building an optical telescope from glow-sticks, not an ideal situation. Solution: the 'space fridge', developed at JPL. . Technically a cryocooler, it allows MIRI to get down to -266 degrees Celsius. Brrr.
A key component of the MIRI cryocooler, a sophisticated 'space fridge'. Image credit: Northrop Grumman
Webb will be able to observe nearby objects in our own solar system and also some of the most distant galaxies in the Universe. It can map areas of sky with images, split the light from objects in order to look at detailed colour information and even block out the light from bright objects to help when looking for faint details. Every instrument on board has been designed with different specialities and modes of operation. This makes Webb a true multi-tasker. It does have a lot of questions to answer after all!
The filter wheel used in the MIRI instrument. Developed by our partners in France/Germany. Image credit: MPIA
Want to know more about Webb? Follow the link below