< Why the most powerful space telescope ever needs to be kept really, really cold

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NASA is preparing to launch the most powerful space telescope ever this month - the James Webb Space Telescope. All of its mirrors and instruments sit on what looks like a shiny trampoline. As NPR's Rebecca Ramirez reports, this is the vital sunshield that has to keep the telescope cold.

REBECCA RAMIREZ, BYLINE: Not just cold - really, really, really cold. Because scientists don't want the telescope's own heat to overwhelm what it's trying to see - faint infrared signals from the first distant galaxies that formed after the Big Bang.

JANE RIGBY: It's going to be amazing, and it's still a little mind-blowing to think about it, right?

RAMIREZ: Jane Rigby is a project scientist for operations of the telescope. She spoke to NPR recently.

RIGBY: We're looking back so far out into space that we're seeing galaxies where the light's been traveling for almost all of the history of the universe.

RAMIREZ: And as light from those galaxies travels through space...

BILL OCHS: It elongates. The light waves elongate, and it shifts into the infrared, which is heat. So to observe the heat, you actually have to get really, really cold.

RAMIREZ: That's Bill Ochs. He's the NASA project manager, and the actual huge telescope is all folded up and packed into a rocket ready to launch from French Guiana. But I met Ochs just outside of LA at a Northrop Grumman facility. That company has been developing the sunshield with NASA, and they've built an exact replica of it to help them troubleshoot any problems after launch.

UNIDENTIFIED PERSON: Hi.

RAMIREZ: Hello.

The clean room it's in for safekeeping is massive. And to get a good look, you got to suit up because the point of a clean room is to keep out any contaminants like dust.

OCHS: So for these, you just put on the hair nets like this.

RAMIREZ: You got to put on a beard net, even if you don't have a beard, a hair net...

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RAMIREZ: ...Clean your shoes and then put booties on your shoes, a smock, wipe down your recording equipment. You get the gist. And anyway, we finally get into the room, and the sunshield's the size of a tennis court - five kite-shaped hair-thin layers of a material called Kapton coated in aluminum. And it's really light. Like, I'm almost afraid it'll rip. In fact, Ochs tells me rips in space are something that they account for. It's why each of the sunshield's layers is made up of 50 pieces stitched together - think super high-tech quilting.

OCHS: And that stitching is also ripstop. So, for example, if a micrometeorite were to hit a layer, it will only tear a little bit. It'll hit a ripstop and it'll stop.

RAMIREZ: The sunshield starts to deploy about three days after launch, once the telescope swooshes past the moon. And the process is methodical.

OCHS: As we go through each of the steps of the unfolding of the sunshield on orbit, we will match that here. So if we have any problems along the way, we actually can come in here and start looking at things in here.

RAMIREZ: It takes a few days for the five layers to unfold. They separate so that there's a gap of several inches between each layer.

OCHS: Once you get them fully separated, that will cool the telescope down to its operating temperatures, you know, tens of degrees above absolute zero when molecules stop.

RAMIREZ: That's around negative 370 degrees Fahrenheit. And getting it that cold is a tough job because the top layer of the sunshield, which gets hit by the sunlight, is a toasty 230 degrees Fahrenheit. The sunshield's designed so that heat dissipates out into space in the gaps between the layers, so the temperature gradually gets colder and colder down to where the telescope's delicate instruments sit in the sunshield's shadow.

OCHS: So you have a more than 600-degree Fahrenheit difference between the bottom and the top, all done by the sunshield.

RAMIREZ: Now, the telescope will be about a million miles away from the Earth - so far away, it cannot be fixed in person, which is why scientists have spent years gaming out what could go wrong.

OCHS: We've developed about 340 or 350 contingency procedures for the spacecraft, but there's always the thing that happens that you haven't thought of.

RAMIREZ: And if something does go wrong with the sunshield, they'll be here in this clean room using this replica of the giant high-tech umbrella to try to figure out a fix.

Rebecca Ramirez, NPR News.

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