The James Webb Space Telescope
JWST Part 5: Keeping Cool
Nerd Out
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Find city profiles, activities and how to join.
Inspiration navigation
Driving change
Inspiring the next generation of engineers to build a more creative, innovative, sustainable world.
News navigation
Latest news & updates
Read all news, updates, and happenings from the Next Engineers initiative.
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Explore all resources
Find the tools that you need to run a successful Next Engineers program, including communication collateral and templates, student and volunteer outreach materials, student activity guides, engineering challenges, and Monitoring & Evaluation resources.
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We are increasing the number of diverse innovators and leaders who will make what’s next for the world even better.
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Hot and Cold
The James Webb Space Telescope is designed to see infrared radiation, the kind of radiation given off by warm things. Webb also needs solar energy to run all its instruments. But if the primary mirror and instruments are bathed in sunlight, they are going to get warm and give off their own infrared radiation. This would interfere with infrared being detected from space.
One of the major engineering problems that had to be solved was how to keep the mirrors and instruments very cold (-220oC or -364oF) while still harnessing the Sun’s energy for power. The solution? A huge tennis court sized umbrella.
know primary
Did you know
Everything in the universe that is even a little warm gives off light. This includes stars, planets, people, and lumps of coal. The hotter an object, the shorter the wavelength of light that is given off. The Sun, being very hot, gives off most light in the visible spectrum. You, being cooler, give off light in the infrared spectrum.
Learn more by watching The Ultraviolet Catastrophe (6:31)
Then you can play with this Blackbody Spectrum simulation from the University of Colorado.
This umbrella or sunshield is made up of five layers of a special material, called Kapton, coated in aluminum. Each layer radiates some of the Sun’s heat away. The layers are perfectly spaced so that as much heat energy as possible can be radiated away.
Have a think primary
Have a think
Why do you think we say something is ‘white hot’?
Visit the UC Santa Barbara's Science Line to see if you are right.
Learn More
This is the coolest thing in space
With the launch of the JWST a lot of fascinating technology is now in space, including a first of its kind cryocooler!
How Does Webb Stay Cold?
Learn more about JWST's sunshield and all its tricks to stay cool.
The Most Sophisticated Mirror in the Universe
Finally, there is that amazing gold mirror. Engineers made the mirror segments out of beryllium – a light and strong metal that is very good at keeping its shape even in extreme temperatures.
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