This is MIRI; the mid infrared camera on board the James Webb Telescope.
Watch what happens when light enters the camera.
A complex series of mirrors and filters direct and split the light up into different wavelengths
which are then resized and directed onto the sensors.
With this camera, Webb can see extremely distant stars and galaxies that are completely invisible to the human eye.
This is only possible by cooling the camera down to just 6 degrees above absolute zero.
But why does it need to be so cold?
In this video we're going to look at how Webb captures infrared light, and how a simple sound like this
is used to cool its camera all the way down to a mind-boggling temperature.
We'll also be giving away this Lego ISS model, so stick around to the end of the video to see how you could win.
All of the cameras on board James Webb detect infrared light, which is invisible to the human eye.
As light travels through space its wavelength is constantly being stretched.
If something is far enough away, the light will be stretched so much that it is no longer visible by the time it reaches us
This means there is a physical limit on how far we can see into space.
Since MIRI's sensors are made from Arsenic and silicon, it can detect this super stretched infrared light
and see beyond that limit.
These sensors work like regular camera sensors by converting photons of light into an electrical signal
but in order to detect the faint signals of infrared light the sensors on MIRI have to be extremely sensitive.
Increasing the sensitivity, however, introduces a lot of noise.
Whenever we point a camera at something, it's sensor isn't just detecting what we want it to see.
There is so much more light bouncing around us that our eyes simply can't detect.
This can trick the pixels in the sensor into registering random levels of light, creating a layer of noise in the image.
If the thing you are looking at has a bright enough signal, it will stand out much more compared to the noise.
However, if the thing you are trying to image is faint like the infrared light from a Galaxy
you'll need to increase the sensitivity of the sensor which in turn will drastically increase the noise.
Since Webb is detecting infrared light, the problem gets even worse.
Every object in our Universe emits heat energy
Some of which is in the form of light.
Most objects aren't quite hot enough to emit visible light
but they do emit a lot of infrared light.
The hotter the object, the more infrared light it will emit
which is essentially how thermal imaging cameras work.
Because of this, James Webb itself would emit so much infrared light
that its sensors would be completely drowned out
and so in order to limit the amount of infrared light produced by the telescope
its cameras need to be kept at a temperature of negative 234 degrees - that is extremely cool.
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In order for MIRI to operate at negative 267 degrees
it's located behind the massive, five-layer sun shield.
This alone reflects so much heat, and cools Webb's cameras down to around negative 234 degrees.
But, since MIRI is much more sensitive than the other cameras
it faces an even bigger problem - dark current.
This is where the atoms inside the sensor itself vibrate and mistakenly register a photon of light creating more noise.
Since temperature is just a measure of how fast an atom vibrates, lowering the temperature will lower the vibration
and therefore reduce the amount of dark current.
Even at - 234 degrees, the vibration of these atoms would be too much for MIRI's sensor
and so they have to be cooled all the way down to negative 267 degrees
just 6 degrees above absolute zero. At this temperature the atoms in the sensor
are almost completely still, drastically reducing the noise and allowing the faint infrared signals to shine through.
But how did NASA take these sensors all the way down to negative 267?
The cooling process all starts here, at the bottom of the telescope with a device called a pulse tube.
Inside these tubes are two Pistons which move back and forth to compress the helium into the pulse tube.
Since this movement would create a lot of unwanted vibration, these Pistons have to move
in the exact opposite direction with precision timing to cancel out each other's movement.
These pistons move very quickly, just like a speaker to create a low frequency sound wave with a frequency of 30 htz.
This sound wave travels down the tube and gets compressed once it reaches the end
creating an area of higher pressure, then as it bounces back in the opposite direction, it expands
creating an area of low pressure before being compressed once again.
If the next wave is sent out exactly as the previous one returns, it means the frequency perfectly matches that of the tube.
This creates a standing wave where the areas of high and low pressure remain in the same place.
By tripling the frequency, it causes the waves to combine and create a stationary wave with
multiple areas of high and low pressure. Since temperature and pressure are related
this also leads to areas of high and low temperature.
This alone wouldn't change the overall temperature
because the hot and cold parts simply cancel each other out, but if there was a way to extract the hot parts
then the temperature would start to drop, and so three heat exchangers made of thin metal sheets
are placed at the points where the hot and cold gas meet, these allow the gas
to pass through whilst also absorbing some of its temperature, causing a heat gradient to form.
The heat from the hot side is pulled out and sent to the radiators via a heat exchanger
then the cold temperatures on the other side are also drawn out. This causes the temperature to drop from 27 degrees
all the way down to negative 256 degrees at the final heat exchanger.
But how is this used to cool the sensors located at the opposite end of the telescope?
Next to the pulse tube is another set of pistons that compress helium
in a completely separate line of tubing.
This line passes through the cold parts of the pulse tube's heat exchangers, cooling the helium
all the way down to around negative 256 degrees.
But still the helium isn't quite cold enough.
From there, the helium goes on a long journey winding its way up through 10 meters of thin tubing until
it reaches the cold head assembly. Inside, there is another heat exchanger and a tiny hole less
than one millimeter in diameter. The helium is pushed through the hole and undergoes something
called The Jewel Thompson effect. As the gas moves through the hole, it gets compressed before quickly
expanding on the other side. This rapid expansion causes the pressure to drop cooling the gas very quickly.
This is why blowing air through our mouth is colder if we make a smaller hole with our lips.
On James Webb, this cools the helium all the way down to just negative 267 degrees.
From here, the helium flows onto copper plates attached to the back of MIRI's sensors, cooling them down to the required temperature.
After that, the helium has done its job and it flows back down the telescope
where the entire process begins again.
When NASA began designing James Webb, no cryocooler with this level of cooling existed
and so, engineers had to really push the boundaries of physics
all wilst conforming to the limits of fitting it into a space telescope.
And now, time for something really special.
The winner of the previous giveaway is Daniel Weinman. Congratulations! But, as always
we'll be giving away another awesome space prize in the next video. To win this amazing Lego space
station model, sign up at the link below and leave a comment saying how long you think
James Webb will operate for. Thank you very much for watching and I'll see you in the next video.