We all know that black things get hot. Just look at these
two identical cars. They’re made out of the same materials
and yet the black one is going to be a lot hotter than the white one.
And that is because it is absorbing a lot of those beautiful sun rays.
Why is Webb’s Radiator Super Black?
Now the James Webb Space
Telescope has two important sides. A hot side and a cool side.
The sunshield blocks the heat on the one side and the mirror observes
on the cool side. It even has a radiator to keep it extra cool.
But everything except the mirrors are black on the side
that needs to be cool? So I was questioning why
are Webb’s radiators coated in this super dark paint?
This paint is made by Ball Aerospace and it’s called Ball Infrared
Black or BIRB. And it’s somehow vital to regulating
Webb’s temperature. So the reason temperature control is
on this telescope is that the telescope observes in the infrared
spectrum of light. Now we may not
but we do perceive it as heat.
And so to get data without any interference from Webb’s instruments
they have to be cooled. I am so ready for this!
To well below -400 degrees Fahrenheit.
Webb’s instruments naturally
create heat as they work, so the radiator
radiates that heat out of it. I’m going to look
and show you here. I’ve got a flashlight we use for inspections.
If you look at it that shiny thing
over here and then look how black that is.
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So why are these radiators black?
Well, as it turns out, things that absorb heat
also emit heat well.
Now the reason black objects absorb and emit heat well involves a lot of math
and a thing called the Stephan-Boltzmann Law. But what it comes down to is that they are
highly emissive. Emissivity is a measure of how
well something radiates heat. And according to physics,
and ideal radiator is an ideal absorber.
I left this board outside for an hour and the side with the black paint
absorbed a lot more solar radiation. And then I went back
at night with the FLIR camera. The black side of the wood
is cooler than the white paint. It is acting like a small radiator.
So it released its energy from earlier in the day much more
efficiently than side with the white paint.
The more emissive a material, the more it can transfer heat.
The Ball Infrared Black paint on Webb’s radiators
happens to be one of the most emissive substances ever
sent to space!
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