- For thousands of years, humans have used the power
of wind to sail across our planet
and discover new lands that were seemingly out of reach.
What if I told you that there's a 400 year old idea
that applies the concept of sails to space
that could make the edge of our solar system accessible
in under 10 years of travel time?
In the hands of the Sith Lord Count Dooku,
a version of this concept was used
when he escaped from Geonosis without a trace.
How could we use sunlight
to assail our travel woes in real life?
(upbeat electronic music)
The sun is a source of plentiful free energy,
and ever since 1608, harnessing it was an idea
that BFF's Johannes Kepler and Galileo Galilei shared,
and it's since inspired tabletop RPG's like Star Traders,
short stories, TV shows, movies,
and actual solar sail missions.
One example of solar sails in movies
is Count Dooku's Punworcca 116, or the Solar Sailer.
It's somewhat of a misnomer since it's not being pushed
by solar pressure, but absorbs energy,
similar to a solar sail to provide energy to the ship.
For someone on the Dark Side, he sure knew how
to leverage clean energy.
Maybe he wasn't so dark after all.
(lightning zaps) Okay, maybe he was!
As space Biggie once said, "Mo-photons, mo-mentum."
Solar radiation allows us to harness the sun
like sailboats use wind.
Each photon that hits your sail is transferring momentum
onto your sail, which accelerates your ship.
Based on the way the sail is angled,
you can change directions, decrease,
or increase a spacecraft's velocity.
In the vacuum of space, you don't have the pesky air
that we have on Earth adding to atmospheric drag
and slowing us down.
There are several designs that solar sails
use in pop culture, like Count Dooku's ship,
and other concepts designed by space agencies here on Earth.
Each one providing an advantage depending
on the maneuvers you need to do
and how you plan on deploying the sail.
The principle of sunlight pressure pushing things
around in space has been harnessed
and applied already in several satellite missions.
For example, Mariner 10 ran out of gas
in their attitude control system,
but flight controllers used this principle
to allow the sun to spin stabilize the spacecraft
by orienting the reflective solar panels
to generate the spin.
Unlike traditional rockets or ion propulsion,
solar sailing is a very unique form of propulsion
that was once thought to be impossible
and still proves to be difficult
even though it has been demonstrated in the past.
Scientists at NASA's Marshall Space Flight Center
are researching ultra lightweight materials
to use as sails, which can advance the use of this method
in the future.
There are many factors that contribute
to the forces that can propel a solar sail.
The largest factor's electromagnetic radiation
emitted by the sun.
Other factors that generate a force
are solar wind, which is 100 times less effective
as electromagnetic radiation, albedo,
which is the reflection and scattering
of solar radiation off the Earth,
and Earth's infrared emissions.
Calculating the amount of flux, or density of pressure
that the electromagnetic radiation from the sun contributes
per square meter at our distance from the sun,
the linear momentum that this flux generates is,
this is a million times less than the pressure
exerted from a dollar bill sitting on the table.
This flux is so small that it falls
below the threshold pressure required for us to hear,
and so, just like that bug that's crawling behind you,
it's too small to detect its presence
with our fancy ear holes.
Well, if our ears were out there in space
listening for pressure exerted by electromagnetic waves,
not hearing the sun would be the least of your concerns.
It's not just about the pressure,
but the total force exerted over the full area of the sail.
The larger the sail, the larger the total force.
The acceleration that you get from a solar sail
can be calculated using this equation
where nu is the sail efficiency
considering that the optical properties of the sail
is not perfect.
Just like a fun house mirror versus a regular mirror,
you want it to be as close to perfect as possible
to get the most efficient use out of it.
P is the pressure generated from the solar radiation,
and sigma is the mass per unit area of the sail
and its components.
Based on this equation,
we can make all kinds of fun calculations.
Let's say you wanna know how big of a solar sail
you would need to transport humans to space.
A solar sail two microns thick
has an approximate acceleration
of around one millimeter per second squared.
This is what you get when you solve the equation
for the area.
Assuming the mass of the spacecraft is divided equally
by the payload structure and sail,
the area needed is 387 meters squared per kilogram
of payload mass.
That means if your payload is a tiny five kilogram
or 11 pound payload, you'd need a solar sail the size
of 1,935 meters squared, or a sail the size
of 4.5 basketball courts combined.
If you wanted to transport the Orion capsule,
which can hold two to six humans
and weighs about 10,000 kilograms,
you'll need a solar sail about four million square meters,
which is the size of 1.2 Central Parks.
Well if you were one of the crew members
accelerating at one millimeter per second squared,
how long would it take for you to get to the moon?
Assuming at constant acceleration, the distance traveled
is calculated by this formula.
Assuming we're starting with no velocity and are relying
on the constant one millimeter
per second squared acceleration
generated from the radiation pressure only,
then the distance traveled is half of the acceleration
multiplied by the times squared.
To see how much time it takes
to travel a 384.4 million meters at that rate,
it will take approximately 10 days.
At the 10 day mark, the vehicle will be traveling
over 877 meters per second, or around 2,000 miles per hour,
which is ridiculously fast.
Likely if this was a real example of sending humans
to the moon on a solar sail, they would have
to start their deceleration upon approach,
and so, it will likely take a bit longer.
Traditional rockets can get you to the moon
in just under three days versus the estimated 10 or so days
using the solar sail.
However, if you want to travel even farther
in our solar system or beyond, the perks of solar sails
really begin to shine.
As payloads continue to be pushed by the sun,
it can reach speeds
that are far beyond traditional rocket speeds.
Similar to the age old story about the tortoise
and the hare, eventually the solar sail tortoise zips by.
This can be a huge savings in both cost and mass.
No matter what method you use,
it still costs somewhere between $9,000 and $50,000
per pound of payload that you're launching into space.
If you don't have to bring all of that rocket fuel,
you're already saving a tremendous amount of money.
It's been calculated that using solar sails
to make routine deliveries to Mars
can save 10's of billions of dollars in mission costs.
That's a lot of cash.
The solar radiation pressure on the sail
also decreases as you travel farther away from the sun
with this pressure decreasing by about half
as you get to Mars's distances
and 10 times less as you pass Jupiter.
Even with that decay,
the free rays still make a huge impact.
Voyager 1 has been trekking along for 44 years,
and it's currently 18.8 billion miles away from Earth.
Scientists calculate that we could catch up to Voyager
in less than a decade using the solar sail technology.
Cool!
Scientists are also looking at Sirius A
as the best target for solar sail traveling
outside of our solar system.
Since the large star can provide a way
to start putting on the brakes for the approach.
Using solar sails, you can get to Sirius A,
8.6 light years away, in just under 70 years.
You can imagine adding lasers pointed at the sail,
which provides a nice boost from us Earthlings.
(bright music)
Is someone shining a light on me (scoffs)?
Space is dark and full of terrors.
The only factor limiting
how fast you cruise the galactic seas
is how well you're material can last
against the elements of space, the mass of your vehicle,
and how far away you are from the sun
or the star that you're using.
LightSail 2 solar sail is made out of Mylar,
which is a polyester film used often
in space-fairing missions for reasons,
such as its dimensional stability and reflectivity.
This Mylar sail has ripstop sown in,
just like a parachute, so that if a micrometeoroid
by chance punches a hole in the sail,
you can still continue to function
while preventing the hole from growing in size.
This Mylar sail is 4.5 microns thick,
or one-five thousandth of an inch.
It's also pretty light.
The entire spacecraft, including the sail,
comes in at 11 pounds.
So, so tiny! (bright music)
With LightSail 2's launch on the SpaceX Falcon Heavy rocket
currently set for late June, we'll be one step closer
to realizing the dream of affordable long-distance travel
by harnessing the free and ever-present rays from the sun.
It's been a long time coming,
and this tech is ready to take us places
because space! (upbeat electronic music)
Thanks for watching this episode of Because Space.
Remember to give us a thumbs up
and if you want to learn more about the LightSail
and The Planetary Society, you can join the mission
over at planetary.org. (bright music)