Crazy Engineering: Flying Solar to Jupiter

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4th of July is coming up and everyone's gonna have some nice ice-cold beverages.

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But do you know where it won't be very sunny, is about a half a billion miles from here near Jupiter.

NASA's Juno spacecraft will be arriving there this 4th of July, making it humanity's most distant solar powered spacecraft. And all of its systems, including keeping it warm, are powered by about the same amount of power this blender currently uses. How is that even possible so far away? Let's find out on this episode of Crazy Engineering.

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Right, we're here with Tracy in this huge room.

Hello Tracy!

Hello!

Can you tell us a little bit about the room that we're standing in?

Yes! We're here in High Bay 1, which is JPL's oldest, largest cleanroom, where we assemble spacecraft.

Ok and what are we standing in front of today?

We are standing in front of one of the test units for a Juno solar array. Juno's a mission that is going to Jupiter to learn more about the planet and how it was formed. This is a full scale test unit and it's one of three on the Juno spacecraft.

Why does it have to be this big?

Jupiter is five times farther away from the sun than the Earth is, and the amount of sunlight you get is decreasing by the square of the distance.

So, instead of 1/5th the amount of power, we have 1/25th the amount of power.

So, we need to have a lot of area on our solar arrays because the spacecraft is so far away from the sun. And also over the last 20 years, we've had about a 50-percent increase in solar array efficiency. And that makes it easier to do at that distance.

If we had these solar arrays here on Earth, they would actually generate about 14 kilowatts of power.

But all the way out at Jupiter, they only generate about 500 watts of power.

These things are so huge and heavy, I imagine it's a bit of a challenge to test 'em on Earth before you go to space.

Yeah, these solar arrays weigh about 250 pounds apiece. Here on Earth, when we tested them, we only deployed one at a time because we didn't have a clean room facility big enough to do all three. And we also had to do them sideways and support them on these posts with wheels on the bottom, so you could gently roll them out and make sure that the hinges and dampers and all of that were working just fine.

Juno is one of the largest spacecraft I've ever seen. How do you package that up onto a launch vehicle?

Our spacecraft is about 65 feet across, with the arrays deployed, and that certainly wasn't gonna work. So, when we launch the vehicle, it has to be folded up small enough to fit into the nose cone of the rocket. And you'll notice that the cells are in the inside and so they wouldn't be getting any power from the sun.

That was a really interesting time for the team during launch, just knowing that we had to make sure the arrays were deployed to get sun, or the spacecraft would just have died.

So, we're deployed. We're absorbing energy. When do we hope to arrive at Jupiter?

We're going to arrive on July 4th of 2016, and the mission is gonna last until February of 2018.

Great! We'll be watching and you guys out there stay tuned for that mission getting to Jupiter and check back again for some other Crazy Engineering.

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