What Will Solar Sail Propulsion Mean for the Future of Space Travel?
Robert H. Goddard couldn’t believe his eyes:
his rocket went finally up to an altitude of 41 feet in 2.5 seconds and landed 184 feet
away. It was March 16, 1926, a date that changed the world. Forever. Today, the Goddard Rocket
Launching Site National Historic Landmark commemorates the site of the world’s first
successful liquid-fueled rocket. You can find it in Auburn, Massachusetts. The original
launch site is indicated by a granite marker. (to the videomaker: show the granite marker)
(and the rocket replica)
Almost 97 years have passed by since that day, and nowadays, the majority of unmanned
rockets that deliver spacecraft and satellites to Earth orbit or on interplanetary expeditions
use a liquid propulsion system, just like Goddard’s rocket. But humans like to look
further, and ever since that day, they have been thinking of ever better solutions: for
instance, we want to go outside the solar system and reach other stars. To do this,
we might need solar sails. As Goddard himself said, “The dream of yesterday
is the hope of today and the reality of tomorrow”.
Let’s explore together the reality of tomorrow learning about solar sails and how they work.
============= Solar sails are a form of spacecraft propulsion
that uses sunlight to push the craft forwards. This revolutionary technology has the potential
to revolutionize space exploration. According to some scientists, we could use
large, reflective sails to capture photons from the sun and turn them into thrust. This
means a spacecraft powered by solar sails could travel much further and faster than
traditional chemical rockets. Theoretically, a craft propelled by this technology could
even travel close to the speed of light. The comparison is straightforward: just like
the wind pushes sailboats across the water, we can use sunlight to fuel a spacecraft.
Isn’t it amazing? Here on Earth, the Sun provides us with the
photons we need to propel these vehicles through space. These particles of light have some
momentum, and when they strike a surface, they impart momentum to it. The idea, therefore,
is to use a reflective lightweight surface on a spacecraft. Literally, a solar sail spacecraft
would consist of a reflective sheet. The photons would bounce off this surface and impart momentum
to it, just like a collision of two billiard balls.
As billions of light particles hit the sheet, they push the sail strongly enough to move
a spacecraft. Over time, the solar particles could keep pushing a spaceship faster and
faster, allowing it to attain very high speeds To work properly, these sheets must be something
like 40 to 100 times thinner than a sheet of paper, and they can be as large as football
fields! So…what kind of material should be used
for this purpose? And what kind of design?
Near-term sails likely will use aluminized Mylar. It is a strong and thin polyester film.
Or maybe they will use CP-1, a space-rated insulating material. Both of them are proven
materials previously flown in space. In the future, more robust sails could be made out
of carbon fibers. The latter offers the most durability but
can be more expensive to produce. Each of these materials has its own strengths and
weaknesses, and the type of sail to be used will depend on the mission.
The design of the sail is also crucial to its success, as it must be lightweight and
strong enough to withstand the harshness of space. There are three basic types of near-term
solar sail designs: the 3-axis stabilized square solar sail system;
the heliogyro sails, and the spinning disc sails.
The first one looks quite much like a kite and uses a rigid structure to extend and suspend
the sail material in space to catch the sunlight.
The heliogyro design was initially considered by the Jet Propulsion Laboratory for a mission
to Halley's Comet. The sail consists of several very long vanes extending from a central hub.
The vanes are deployed from rollers by spinning the craft.
The centripetal force pulls the sails outwards, unrolling them. The vehicle continues to spin
in order to keep the vanes tight. It steers by tilting the vanes, which redirects the
solar pressure. The heliogyro is an attractive option because it requires minimal fuel and
it is highly efficient. It is capable of accelerating to high speeds and it is maneuverable, making
it suitable for interplanetary exploration. Its lightweight design also makes it attractive
for larger mission designs. Despite these advantages, the design has several limitations,
most notably its complexity, lack of redundancy, and lack of qualification for use in deep
space.
The spinning disk sail has a number of advantages. This configuration also uses rotation as a
means of tension across the film similar to the heliogyro. Though, the spinning disk has
a continuous sail film. (
A distinctive feature of the spinning disk is that it can also passively deploy by using
rotation.
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to the channel? ========
Anyway. That sunlight exerts a small amount of pressure as photons bounce off a reflective
surface, we knew since the early work of James Clerk Maxwell. But to be sure, we needed some
experiments. In 1960, NASA sent a metalized balloon satellite,
called Echo-1, to space. It was the first passive communications satellite experiment.
Scientists wanted to make sure we could use satellites as a means of communication from
one location on Earth to another. Among other things, the spacecraft was useful in the calculation
of solar pressure, due to its large area-to-mass ratio. Photon pressure played orbital soccer
with the Echo-1 thin-film balloon in orbit, and the shards were flung far and wide by
sunlight. Later on, in the '70s, JPL led a project to
try the first solar sail flight. Halley's Comet was to make its closest approach
to Earth in 1986, and NASA conceived the exciting idea of propelling a probe via solar sail
to rendezvous with the comet. Eventually, the project was scrapped.
A lot of other experiments, from all over the world, going from Russia to Japan to America
and Europe, have been done.
By the end of the 20th century, however, no solar sail had been deployed in space. Many
automatic probes, starting with Mariner-10, did use the mechanical effect of sunlight
on their solar panels to change their orientation, but this method was never applied to propel
a ship.
The Russian Znamya-2 — did reach orbit in 1993, but it was used not to obtain thrust
from light, but as an experiment on illuminating the Earth’s surface with an orbital mirror.
And even this experiment ended in nothing. The Planetary Society’s first crowdfunded
solar sail mission, Cosmos 1, was also launched in 2005, but it failed to reach orbit.
Finally, in 2010, Japan’s IKAROS spacecraft was the first spacecraft to use controlled
solar sailing as its sole method of propulsion.
It was a kite solar sail that flew by Venus
at a distance of 80.800 km, successfully completing its planned mission. On 30 November 2012,
JAXA announced that IKAROS had been recognized by Guinness World Records as the world's
first solar sail spacecraft between planets and that its two separated cameras, DCAM1
and DCAM2, had been recognized as the smallest size of a spacecraft flying between planets.
Solar sail technology makes it possible to
explore distant stars and planets in a way that was previously unimaginable. This technology
could allow spacecraft to reach the outer regions of our Solar System and beyond, opening
up possibilities for future exploration. Solar sail propulsion could also enable us
to explore the universe in a new way. By harnessing the power of the sun, a solar sail spacecraft
could slowly and consistently accelerate, allowing us to explore distant stars in just
a few years.
Actually, scientists had an idea: knowing that solar light can accelerate our lightweight
sail, what about trying to build a whole system of light beamers and light sails in order
to reach other worlds? This would also allow space travel at a significant
fraction of light speed. The brilliant idea is to build a ground-based light
beamer pushing ultra-light nanocrafts – miniature space probes attached to lightsails –
to speeds of up to 100 million miles an hour. Such a system would allow a flyby mission
to reach Proxima Centauri in just over 20 years from launch! This is amazing! A project
like this already exists! It’s called Starshot. Using advanced miniaturization, sensors, and
communication systems, this spacecraft will travel more than 20 years to reach its destination.
However, given the little size of the lightsails, and their high speed, there are a lot of unsolved
problems and questions to be answered. For instance, how are we gonna navigate a so small
sail at this speed, in interstellar space? What kind of material should we use in order
for the sail not to burn or break apart? We would need a material that is ultra-light,
extremely reflective, and almost completely nonabsorbent, while being rigid and stable
enough to withstand the force and heat of acceleration! And most importantly, will we
be able to send image data back to Earth?
It’s a hard task. PhD positions are now open to find answers to all these questions.
If we ever managed to do so, we will be probably able to send home images of the recently-discovered
exoplanet Proxima b, and any other planets that may lie in the system!
The future of interstellar exploration is
bright, and the Starshot project could be the first step into a universe of possibilities.
As you can see, the possibilities opened up
by solar sail technology are vast and exciting. Solar sail propulsion has the potential to
revolutionize exploration and expand humanity's understanding of the universe.
In the future, solar sail propulsion could become the primary method of interstellar
travel. Combined with other emerging space technologies, such as ion engines and nuclear
reactors, it could enable us to explore the deepest reaches of the universe.
Hey! This video ends here! What do you think about solar sails? Let us know in the comments
below! See you soon on the channel!