How Solar Sails Are Remaking Space Exploration

The year: 1974. The location: outer space
between Venus and Mercury. NASA's Mariner 10 probe
had a serious problem. Because of some unplanned maneuvers, they were running much lower
on propellant than expected and in order to maintain
control of the spacecraft, NASA had to come up with a workaround. If they didn't do something quickly, the probe could miss Mercury altogether. That's when engineers came
up with an ingenious plan. And what they ended up doing was using the solar
panels of the spacecraft and just angling those panels
with respect to the sun and letting sunlight pressure move and position the
spacecraft as needed. And it worked. Mariner 10 became the first
probe to fly by Mercury, giving humans the first
close-up images of the planet.

This close call showed that solar pressure could be used to keep a probe on course just like a sailboat uses the wind. So NASA was able to successfully sail with Mariner 10, even though that was not part of the original mission design. Solar sailing uses an existing, almost limitless energy
supply from the sun. If you have a light on right now, or are in the sunlight, you might be surprised
to know that that light is pushing you.

Well believe it or not, sunlight actually does exert a force on us. If you go outside on a bright, sunny day, you're probably feeling the equivalent of maybe the same amount of force as a very light feather might exert resting in the palm of your hand. It's not very much and
we don't even notice it because even the slightest breezes will easily overwhelm our sense of being pushed. But in space, it's a very different story because there is no ground
to anchor yourself against. There is no other wind or breezes or other forces acting on you. So, ever so slowly but surely that sunlight
pressure will build up and will very gradually
accelerate you away. Solar sailing was first written about by Johannes Kepler in 1610 who thought a space sail
might one day capture sunlight the way a boat sail catches the wind. Although he didn't fully
understand the mechanism to make this a reality, it was later theorized by
physicist James Clerk Maxwell, who mathematically showed that sunlight carries momentum that
exerts pressure on objects. If you get in the near vacuum of space and you have a low-mass, low-weight object and a shiny, reflective sail that the light can bounce off of, you can actually use it
to propel a spacecraft.

Or at least that's the theory. Solar sailing offers a possible solution to one of the largest obstacles
facing space missions today: a limited fuel supply. Once you use up all of your propellant, you've got nothing else to push with. And that's a fundamental
limitation of rockets. But with successful solar sailing demonstration missions by the Japanese Aerospace Exploration Agency, NASA, and most recently the Planetary Society, missions could now be longer, cheaper, quicker and go farther out
into space than ever before. It really opens up the
solar system for exploration on a scale that we cannot come close to with our current technology.

Astronomers sometimes
say that space is curved. People like Carl Sagan, the co-founder of the Planetary Society, saw the potential it
had for future missions. Now what will this do? Well, it takes you to where you wanna go. So one mission that's being talked about is to rendezvous with Halley's Comet. I've always wanted to do that. He would inspire a generation to make his dream a reality
years after his death. But the Planetary
Society's first solar sail, Cosmos 1, never made it into orbit after a rocket failure in 2005. It was the Japanese Aerospace
Exploration Agency's IKAROS that became the
first to demonstrate solar sailing in 2010. And a year later, NASA's
NanoSail-D did the same in low-earth orbit.

But it's the development
of even more recent technologies that are starting
to enable real missions. The key enabling technology
behind solar sailing isn't so much the sail, it's making the payload as small and lightweight as possible. And in recent years, we've developed what's called CubeSat technology. We even have what's
called NanoSat technology. And these are tiny satellites that can weigh less than a kilogram and contain all of the
electronics necessary to conduct a mission. Everything from your
avionics, your communication, attitude control, navigation, everything all baked onto
a few chips of silicon. So these CubeSats,
coupled with a solar sail, make for a very effective
yet very low cost payload.

This combination of solar sailing and lightweight craft, when used together, could make space exploration cheaper and more accessible to everyone. And the Planetary Society set out to prove that it could be a practical option. In 2019, their super lightweight CubeSat the size of a loaf of
bread, called LightSail 2, launched aboard the SpaceX Falcon Heavy. So LightSail 2 launched as a
CubeSat that was this size. This is a one-to-one cardboard version. And once it got in orbit, it opened up solar panels exposing inside the sail material and some of the
instrumentation, the cameras. Then we deployed the sail, which is about the size of a boxing ring, 32 square meters, and it deployed these
four triangular sails that come out of the loaf of bread. The material of the sail itself is Mylar, so like Mylar balloons
but actually thinner. It's about four microns in width, micron being one
millionth of a meter, so it's very thin and
to keep it from ripping, it's got so-called rip stops, which are strings that
are in a hash pattern. Light from the sun, which is made up of photons, hit the shiny Mylar
material carrying momentum, bouncing off and causing a push.

The team then used a momentum
wheel to steer the spacecraft. LightSail 2 was the first ever mission to successfully maneuver in
space using solar sailing. The main goal with LightSail 2 was to demonstrate
controlled solar sailing in a small spacecraft,
specifically CubeSat, and we did accomplish that. And it's still sailing. But this is only the beginning. In the next few years, NASA's Artemis 1 will head to the moon and on board will be a solar sailing mission called the Near Earth Asteroid
Scout or NEA Scout. Once in space, it will
separate from Artemis, and travel to an asteroid
within three years after its launch. So we actually have an
agreement with NASA. So we're working directly with their Near Earth Asteroid
Scout solar sail mission and working together to feed
forward what we're learning.

But solar sailing isn't only confined to the inner solar system where there's plenty of sunlight. Quite the opposite. It could offer the best way to reach the outer
solar system and beyond. But it will need to improve
from its current technology. One of the main disadvantages with current solar sail designs is that they are monolithic, which means that you
ultimately have to pitch, roll and yaw the entire sail. But if you can break the
sail up into component parts, you can then individually articulate each of those components and you can gain a lot
more maneuverability. And that's what a company called Xplore are working on with their SunVane concept. SunVane takes a really large sail area and breaks it up into six
or eight individual vanes. The vanes can then be
independently articulated.

That would make SunVane a
highly maneuverable sail. And the advantages of high maneuverability mean that you can reach
a target destination that much faster, because you can plot a more direct and a more efficient course to get you from point A to point B. The SunVane will tack
inward toward the sun, like a sailboat tacking into the wind, and then turn its vanes toward the sun for maximum acceleration. The technology demonstration, which is still in the
initial planning stages, aims to reach speeds of
5 to 8 astronomical units or AU per year. One AU being the average distance
from the Earth to the Sun. That will make the SunVane
demonstration mission the fastest man-made probe ever launched, reaching Jupiter in less than a year.

All without a drop of fuel. But considering the
great distances of space, it will need to go even faster and fly even closer to the sun to accomplish the kind
of deep space missions scientists are hoping to achieve. But so far the technology isn't there. Well, the temperatures in that environment are going to be extremely high. So you need very lightweight
yet very durable materials. So some advanced materials
that might come along might be something like silicon nitride or silica sails. These materials don't yet exist, but there are companies that
are working on developing them. Another limitation is that solar sails won't easily be able to carry
anything heavy, like a person. To propel a larger payload, say a crude payload, well, you're going to
need a very large sail and a lot of time to get to
a sufficient enough speed unless, of course, you
wanna send your crew into a sun-dive maneuver.

But that might not be very
good for their health. But for smaller craft, the possibilities are limitless. The most ambitious
mission using solar sails even involves visiting
another solar system, and would allow us to reach
our nearest star system, Alpha Centauri, in just 20 years. It's called Breakthrough Starshot. So Starshot envisions using
an array of terawatt lasers, concentrating their
light on a tiny sailcraft that weighs less than one gram. In that one-gram package
contains the sail, spacecraft, a camera,
a transmission antenna, everything, all hyper miniaturized. The NanoSails would accelerate
at something like 10% the speed of light and potentially reach Alpha
Centauri in about 20 years. While the technology is nowhere near making Breakthrough Starshot a reality, solar sailing is entering its next phase. Missions that were once huge endeavors because of the cost and size will soon be able to launch
as secondary payloads, piggybacking off other missions.

That means visiting asteroids,
moons of the outer planets or even interstellar objects that enter our solar system could be achieved much more easily. You get an infinite amount of sunlight that is never ending, so you leave your fuel on the ground and you just continue to sail. So it's not like sailing by sunlight is going to replace chemical rockets, but solar sailing will allow us to do more than what we can do with
chemical rockets alone. This technology is important
for future missions because it's an enabling technology. It enables you to do missions with solar-weather monitoring that you couldn't do otherwise, poles sitting on planets that
you couldn't do otherwise, doing multiple encounters and having a flexibility to adapt that you couldn't do otherwise.

And someday maybe doing
interstellar missions, which you couldn't do otherwise..

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