Bill Nye Explains the Science Behind Solar Sailing

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For decades the prospect of interplanetary travel

has been restricted by fuel.

But one organization is working

to use light from the sun to travel to the stars.

[Technician] Three, two, one, zero.

The Planetary Society recently began

the first orbital test of their LightSail 2 spacecraft

and it's already started sending back images.

If solar sailing proves to be

a viable means of propulsion

it could one day be used to explore the galaxy.

To learn more we brought in

the Planetary Society's CEO, Bill Nye.

Hi Bill, so congratulations on the successful mission

how's the light sailing going?

Sailing is going very well.

So we have a small spacecraft, it's in orbit

and it's getting a push from the Sun every orbit.

It's very exciting, you know,

I was in astronomy class in 1977

and Carl Sagan was talking about a solar sail mission.

How long ago was that 42 years ago?

And now we finally pulled it off.

We are sailing on sunlight.

So can you tell us a little bit

about how the light sail works?

I happen to have a model right here.

So this is 1/10 size of LightSail 2.

So this is the Three Unit CubeSat here in the middle.

And so its 30 centimeters by 10 centimeters

by 10 centimeters to give you perspective.

That's almost, but not quite as big

as a conventional loaf of bread.

And then this is 32 square meter sail.

So it's about the size of a boxing ring.

And even if you've never been to a boxing ring,

you've seen one the TV.

So sunlight hits these solar panels

here on the spacecraft, by a long tradition

the main part of a spacecraft is called the bus.

The sails comes [zipping] out of the bus,

out of the main cube and they get to be

relatively this big.

And this is the real material,

feel it, Daniel, it's crazy thin isn't?

Yeah. Get in from

the edge we have reinforced the edge

to make it more durable for carrying.

But feel how thin that is? It's like

hardly there. Much thinner

than human hair, and you can see

the rip-stop feature in the sail material.

So sunlight hits it and gives it a push.

It's just out of your everyday experience

that light can push something.

And so we found that the sails

do billow a little but, just like

sails on a sailboat.

And we found that because here on these panels,

we have cameras, two cameras.

And they're gorgeous, you see the shots

of the Earth below with the sail in the foreground.

And so it'll fly and we twist 90 degrees

with every orbit because in here is,

what nowadays people call a momentum wheel,

but you might of used to, you might used

to have called it a gyroscope,

a spinning wheel can produce torque

to twist the spacecraft in space.

It's just amazing, and this has been

a human dream so you could put this,

a spacecraft like this, in an orbit

closer to the Sun than the Earth is,

now the closer you are to the Sun,

the faster you go around.

Mercury goes around faster than Venus,

which goes around faster than the Earth.

The Earth goes around faster than Mars and so on.

But what you could do, is be as close

to the Sun as Venus, but because solar pressure

is hitting your sail, you could keep in line

or keep station with the Earth.

And the practical application for that

is monitoring what we call solar weather.

If there's a coronal mass discharge

of particles from the Sun going at the Earth,

you could get five or six hours warning

which could be priceless.

In 2012, there was a solar, coronal mass ejection

of particles that just missed the Earth,

crossed the Earth's orbit about two weeks

behind us, as Earthlings.

If that were to hit our communications satellites

and ground based systems, it would be

a catastrophic catastrophe.

The other thing is from that position in orbit,

around the Sun, you could watch for asteroids.

As the saying goes, Looking for an asteroid

is like looking for a charcoal briquette in the dark.

Very difficult to see at optical wavelengths.

But in the infrared, in the just a little

above Absolute Zero in heat, you could find 'em.

And there are 100s of 1,000s of asteroids

that cross the Earth's orbit.

Some fraction of those would be the end of the world.

So we wanna find those. Worth looking out for.

That's right, the preventable natural disaster.

Very low probability, very high consequence.

And so when this spacecraft is launched,

it's about the size of loaf of bread,

right? It's actually

smaller than a loaf of bread by a little bit.

[Daniel] But it unfurls to the size of boxing ring?

Right. Can you

kinda walk me through the process

of how that's done? A standard has emerged

in spacecraft called a CubeSat, cubical satellite,

and this happened because universities

wanted to build these things,

the Air Force is involved in this

and so you can go online and buy parts

for cubical satellites and the standard is

10 centimeters by 10 centimeters

by 10 centimeters, X, Y, Z, a cube.

Well then the standards emerged

so we have a 10 centimeters

by 10 centimeters by 30, so it's what you call

a Three Unit, or Three U Cube Sat.

And in there is a little, literally Swiss motor,

like a Swiss watch, this very, very small motor

on this crazy small, very precisely made gear train

the booms are very much like tape measures,

they're thin, steel ribbons

and they wind up into this very small volume.

They get very, almost flat.

And so we have a motor that pushes them

to get them started and then it holds them

back so they don't go [zipping]

out too fast and tear the sail.

And this was something, this is classic engineering problem.

You think, you might think,

if you wound up these springs they would just deploy,

just un-spool on their own.

But they don't because the material is curved,

and when you flatten it, the curve changes

and the stresses change.

We have software that commands

the motor to un-spool the, to deploy the booms.

Then the sails are attached to the end

with little springs 'cause the heating

and cooling as you go around the Sun is,

makes the booms change length by a little bit,

and so figured that out too.

And the crazy thing is the sails are made

of this Mylar material that's 20 microns.

This is crazy, and so you can pack

this huge, shiny silver sail

into these very small volumes.

It's origami. So this is

a CubeSat, and you've managed

to raise the orbit of this CubeSat.

Is this, looking to the future,

is this something that could ever be used

to one day bring humans to other planets

or even other stars? Humans,

almost certainly not, the problem with humans is

they're heavy and we are not electronic.

We need to drink and recover the water that we get rid of.

And it's very, very, it's a massive system

to support a human, but going to another star system,

a solar sail is really the only technology

anybody can think of right now that would enable that.

And what you would do, you'd build

something like LightSail 2.

And you'd put it in orbit,

and then you'd hit it, or push it with laser beams.

Then you would create laser beams here on Earth

with an enormous amount of electricity

and shoot 'em at the spacecraft

and push it to another star system.

And keep in mind, if you were to do that,

even a spacecraft the size of a postage stamp

would show up in the Proxima Cenaturi,

Alpha Cenaturi solar system, four light years away,

it would show up there with the energy

comparable to a small nuclear weapon,

like a Hiroshima-style bomb.

And so if it were to hit something,

well okay, we're from Earth, cool.

[explosion] I sent you this bullet

that's enough to you know, it's a great way

to say hello. Destroy a city, yeah.

So I'm not saying it would, it just,

don't get carried away everybody.

It's like, not a solved problem.

The other thing that everybody's really enchanted about

is exploring nearby space.

And by nearby we mean the Kuiper Belt

where all these icy objects are orbiting the Sun

with a solar sail that got out there

because it could get up a 100 kilometers a second.

So what you would do is have a solar sail

that might have the same shape

as LightSail 2, but the materials

it would be made of would be able to

hold their shape, their integrity, close to the Sun.

So you'd send the spacecraft in nearer the Sun

and you'd have so many photons hitting it so strongly

that it would push it out at a 100 kilometers

and you could get out to, way out,

in the solar system relatively fast.

That technology doesn't exist right now.

The materials don't exist right now.

But the longest journey starts with but a single step.

So we like to think of LightSail 1 and 2

as part of the overall mission

of advancing space, science and exploration.

That's what we do at the Planetary Society,

citizen funded flight by light.

Well congratulations on taking

that first step and thanks so much

for joining us Bill. Thank you Daniel.

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