James Webb Space Telescope Part 5: Keeping Cool

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.

JWST Heat Shield - NASA — *An illustration of the difference in temperature on the hot (Sun) and cold side of Webb. Image by NASA used under fair use*

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.

JWST Sunshield - NASA — *Illustration of the fiver layers of the sunshield and how each layer contributes to radiating away some of the Sun’s heat. Image by STScl is used under fair use*

JWST Layers of Sunshield NASA — *The five layers of the sunshield. Image by Northrop Grumman is used under fair use*

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!

Watch video

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.

Watch now

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