[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/IKAROS_solar_sail_3853.jpg]]
[[caption-width-right:350:This image depicts the [[UsefulNotes/{{JAXA}} Japanese]] IKAROS spacecraft, which used its solar sail to control altitude and rotation speed. Yes, this trope is TruthInTelevision.]]

->"In frigid darkness they slept, and as they slept, the cold winds of light between the stars swept them onward, slowly..."

So you've got your nice big spaceship, but you have one big problem - fuel. It's heavy and runs out real quick.

The solution? Build a paper-thin mirrored sail a hundred kilometers across, and hang it in front of your ship - the pressure of light from stars will slowly propel your ship outwards. As you get closer to a star, you get more thrust, and as you get further away, the thrust drops off according to the inverse-square law. Using the thrust to move directly away from the sun is rarely the goal, since the acceleration is low and continuous and doesn't usually equal the sun's gravity.

Like a sailing ship, which uses the contrary force vectors of the water and the wind to choose its direction, a solar sail ship uses the contrary vectors of the sun's gravity (always in) and the sun's light (straight out). A sail ship angles relative to the sun to either increase or decrease its tangential orbital velocity, and therefore the radius of its orbit. In some cases, a solar sail might be used to "hang" a ship or satellite over a star in a place orbital mechanics don't allow (see: DysonSphere), but in this case it's more of a solar parachute.

Unlike a sailing ship at the waters, however, a solar sail cannot "tack" into the solar wind. Tacking requires a keel submerged in a medium with much greater drag (e.g. water), which a solar sailing vessel lacks.

A close cousin is the magnetic sail, a system that uses a huge conductor (kilometers of superconducting wire or a cloud of ionized gas) and a magnetic field to steal kinetic energy from passing solar wind. Since the charged particles streaming from the sun are more massive than photons, this system delivers more thrust, but it requires input energy, and isn't as visually interesting since the "sail" is invisible.

For interstellar voyages, the ship is usually propelled by a giant [[FrickinLaserBeams laser cannon]] in space shooting at the sail.

Real-life solar sailing is limited to attitude and rotational control, but it has still advanced by quite a lot despite the technology's infancy - Japan has already sent a solar sailing spacecraft on a Venus flyby trajectory in 2010, and other agencies and groups are planning to launch solar sails for purposes other than to test the sail itself.

Common in [[MohsScaleOfScienceFictionHardness hard science fiction]], or as TechnoBabble for SpaceSailing starships.

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!!Examples
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[[folder:Anime]]
* The ''Odette II'', the yacht club's training vessel (and a former pirate ship), in ''LightNovel/BodaciousSpacePirates''.
* The ''Anime/MobileSuitGundamSeedDestiny'' ''Stargazer'' ONA has the "[[TitleDrop Stargazer]]" Gundam. It uses a Voiture Lumiere system as a magnetic sail. It is meant to be an unmanned probe controlled by a rudimentary AI for extrasolar exploration, though it can carry a couple of passengers/pilots if necessary. It also takes the Gundam about a month to make it from Venus to Earth using just the Sun's output for thrust (it rode a giant particle beam to get out to Venus in the space of a couple of minutes).
* ''Anime/MartianSuccessorNadesico'' used this brilliantly. To lure out a hidden Jovian weapon that's been attacking them, Yurika shuts off the Nadesico and has the Aestivalises hooked up to solar sails to keep them powered up, making it akin to fishing. Once the weapon is finally revealed, everything's reactivated and the crew forces it to escape.
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[[folder:Comics]]
* Highly obscure Creator/MarvelComics character Starhawk had these built into his spandex super-suit, one set one his back and a matching set on his head. Which is impractical and unlikely, [[RuleOfCool but...]]
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[[folder:Film]]
* The ''Venture Star'' in ''{{Film/Avatar}}'' uses a solar sail to accelerate to its destination several lightyears away. A laser in the Sol System provides thrust for the sail to get up to 70% lightspeed. However, the ship uses an antimatter rocket to slow down when it reaches Alpha Centauri. The reverse is true on return trip: accelerating away from Alpha Centauri with antimatter rocket and slow down to Sol with laser.
* Count Dooku in ''[[Film/AttackOfTheClones Star Wars: Episode II]]'' uses a ship equipped with a (unrealistically small) solar sail to escape from a battle.
* Jim Hawkings' sailboard and the RLS Legacy from ''Disney/TreasurePlanet'' are referred to as solar sails, but they have little in common with actual solar sails.
* In ''Film/{{Tron}}'', a simulated vehicle called a Solar Sailer is stolen by two of the movie's protagonists to make a hasty exit from the facility where it just happens to have been under construction. To avert the need for steering, a Solar Sailer's path follows the path of whatever data beam it rides on. A much larger version is used in ''Tron Legacy'' for bulk transport of [[spoiler:abducted programs]].
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[[folder:Literature]]
* The Martians in ''Literature/LastAndFirstMen'' by Creator/OlafStapledon, being creatures whose body is composed of trillions of nanoscopic (not microscopic) viruses that communicate on a central nervous system of radiation, are able to conform their bodies into thin solid sheets that can traverse interplanetary distances. This is how they reach an Earth inhabited by the Second Men to begin their crusade to 'liberate' terrestrial diamonds which they believe are being handled sacrilegiously by the planet's dominate species, which the Martians also mistakenly think are the humans' radio devices.
* A derelict alien-built solar sail vessel appears in ''Decency'' by Creator/RobertReed. The sail is wider than the Moon, and is punctured from impacts with stray atoms of dust in interstellar space. When it impacts with the Earth, the impact itself is harmless due to the sail being so fragile.
* The arrival of an alien solar sail vessel in a human colonized system in ''Literature/TheMoteInGodsEye'' starts off the plot - although this one was the variation that is initially accelerated by a planet-based laser emitter.
* ''The Wind from the Sun'' by Creator/ArthurCClarke is about an international race by solar sailing ships from the Earth to the Moon, patterned on America's Cup style yacht racing.
* Creator/RobertLForwards's ''Rocheworld'' series features solar sails heavily. They are used for cargo vessels in the solar system, and the interstellar ship sent to the Barnard system uses a solar sail propelled by a laser on Mercury.
* Solar sails are used as weapons in Creator/AlastairReynolds' ''Literature/RevelationSpace'' trilogy - a monolayer solar sail does wonders at killing the starships flying at 90% the speed of light. In an interstellar chase, a sail is released behind the ship being pursued, and a powerful laser pushes the sail back towards the pursuer; with the speed difference between the two objects, contact would result in instantaneous destruction.
* [[TropeMaker The original]] StarfishAliens, the Elder Things introduced in Creator/HPLovecraft's ''Literature/AtTheMountainsOfMadness'' have fan-like wings that act as biomechanical ones allowing them to fly through space in the nude. [[BatmanCanBreatheInSpace They're apparently very good at holding their breath]]. (Although holding your breath in outer space would be a really bad idea as the air inside your lungs will expand and rupture your insides)
* In the Russian collaborative novel ''The Road to Mars'', the [[MultinationalTeam multinational crew]] of the ''Ares'' receives orders from MissionControl to beat the Chinese ''Millennium Boat'' in a race to be the first humans on the red planet. TheCaptain of the ''Ares'' has the crew adjust the course to get dangerously close to the Sun in order to shave off a few hours and orders the crew into the living pod in order to shield everyone from increased heat and radiation. Just then, he gets a message from MissionControl, letting him know that there is a secret container aboard the craft, containing an experimental solar sail (the knowledge was kept secret in order to allow the company to file a patent on the new lightweight material). He is also told that a solar flare is about to occur just as they're passing the Sun. This will not only allow the sail to unfurl and give them the needed boost to beat the Chinese, but the magnetic field will also shield the craft from radiation, allowing the crew to go EVA to set up the sail ([[spoiler:unfortunately, a tool failure results in one of the crew members receiving a lethal dose of radiation]]).
* Nathan Lowell’s [[http://www.solarclipper.com Golden Age of the Solar Clipper]] series has the titular ships using the magnetic sail variant to cruise out of star systems on the solar wind, then use a jump drive to reach the edge of the next system and a “gravity keel” to tack against the solar wind there.
* ''Avengers of the Moon'', by Creator/AllenSteele. The ''Creator/LeighBrackett'' makes use of an enormous lens located at a Lagrange point near the Moon to concentrate photonic energy against its sail. Smaller vessels use it as TheMothership to carry them to Mars. This becomes a plot-point when a saboteur tries to detach Literature/CaptainFuture's spaceship from its mooring cradle so they'll be [[DramaticSpaceDrifting stranded in space]], as a vessel with this form of propulsion can't just stop and pick them up again without becoming stranded themselves.
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[[folder:LiveActionTelevision]]
* ''Series/StarTrekDeepSpaceNine'' has Captain Sisko recreate an ancient Bajoran spacecraft with solar sails. Supposedly it made it all the way to a neighboring star system, though some characters doubt the voyage could be achieved at sublight speeds. [[spoiler:Turns out the sails can also catch tachyons in order to travel FasterThanLight.]]
* TheReveal in ''Series/TheOuterLimits1995'' episode "The Message" is that the 1s and 0s the woman keeps furiously scribbling at 3:10 AM every night are a cry of help from an alien ship that is propelled by a solar sail. The ship is moving on a trajectory towards the Sun, much too fast for the solar sail to stop. They instruct the woman how to build a high-energy laser to push the craft onto a safer course. It works.
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[[folder:RealLife]]
* The Japanese [[IcarusAllusion IKAROS]] ([[https://en.wikipedia.org/wiki/IKAROS Interplanetary Kite-craft Accelerated by Radiation Of the Sun]]) space probe was launched in 2010. It was the first spacecraft to use a solar sail as its main method of control (a traditional chemical rocket placed the probe on its Venus flyby trajectory) and was the first interplanetary solar sail spacecraft. The craft's journey to Venus was intended to test the sail's control system - LCD panels on the sail itself can adjust their reflectivity, giving the craft a method of attitude control. Cycling the panels on and off also allows the spacecraft to control its rotational speed. Since its launch in 2010, IKAROS has completed its original mission successfully and now orbits the Sun once every ten months, periodically waking up and transmitting data back to Earth.
* NASA's first attempt at launching a solar sail-powered craft was much less ambitious- the [=NanoSail-D=] mission was designed to test a solar sail in low Earth orbit. The first launch in 2008 failed, destroying the probe; however, a launch spare was modified and improved to become [=NanoSail-D2=], which was launched successfully in 2010, after IKAROS was launched. Unlike IKAROS, [=NanoSail-D2=] does not exist anymore - it reentered the atmosphere and burned up as planned.
** Although [=NanoSail-D2=] was NASA's replacement for [=NanoSail-D=], the original [=NanoSail-D=] mission was handed to the non-profit Planetary Society. [=NanoSail-D=] was renamed [=LightSail-1=], and although [=NanoSail-D's=] successor had been launched successfully in 2010, [=LightSail-1=] still awaits launch. The Planetary Society had earlier tried to launch in 2005 the first ever solar sail-powered spacecraft, Cosmos 1, but the launch vehicle failed to reach orbit.
* Proposed as a far less dangerous method of dealing with a [[ColonyDrop meteor heading towards Earth]] than [[DeusExNukina launching a giant nuke at it]]. A robot spacecraft would attach a solar sail which would gradually pull it off course - if the meteor is caught early, even the minuscule acceleration from a solar sail is enough to change its trajectory substantially by the time it comes close to Earth.
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[[folder:RolePlayingGames]]
* ''CentauriKnights'' uses beam-assisted magsail ships as the only means of travel between Alpha Centauri and the Sol system. They travel at a significant fraction of light speed, but the trip still takes seven years.
* ''TheJovianChronicles'' have solar sail and mag-sail craft as the primary bulk cargo carriers. The trade fleets operate from Mercury, because its central location next to the sun makes it a convenient stopping point. Solar sails are used in the inner systems, but only magsails are practical to reach the Jovian colonies and the asteroid belt. Past that, the solar wind is so diffuse that the Jupiter to Saturn trade relies on fusion-powered ships - fortunately there are big sources of hydrogen at both ends of that run.
* An optional technology in ''TabletopGame/{{Traveller}}'', but usually too slow to be worth it except for sport.
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[[folder:TabletopGames]]
* In ''TabletopGame/BattlefleetGothic'', Eldar Craftworld and Corsair starships are propelled by large solar sails. In game this is represented by Eldar ships having three movement speeds representing whether they are moving towards, away from or parallel to the sun, meaning that they have to tack like a sailing ship to get the best speed across the battlefield.
* ''TabletopGame/BattleTech'' Jumpships and Warships use jump sails to recharge their jump drives. The sails take a long time to set up and it takes a week to fully recharge the drives. It's worth noting that in this case the sails only act as basically giant flexible solar panels; any actual sublight ''propulsion'' worth mentioning is done via fusion rocket, it's just that the average [=JumpShip=] is essentially just a single FTL drive core with some station-keeping engines and quarters for the crew as an afterthought.
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[[folder:VideoGames]]
* Starting in ''Videogame/SpaceEmpires IV'', you can place solar sails on your ships for bonus movement. They still work even if there isn't an actual star in the system, though.
* The ''Interstellar'' GameMod for ''Videogame/KerbalSpaceProgram'' is a roughly 2500m^2 square sail. It has a truly pathetic amount of thrust even when close to the sun, but it's fairly lightweight and has infinite delta-V, useful for trimming interplanetary orbits. Navigation with the solar sail is DifficultButAwesome, as its flight mechanics are completely different from traditional rockets and only receives thrust with the sun in direct line-of-sight.
* A random event in ''Videogame/{{Stellaris}}'' has you discovering a derelict solar sail ship. Sadly, you can't reverse-engineer the tech to use it yourself, but you do get some bonus engineering research off of it.
* ''VideoGame/TreasurePlanetBattleAtProcyon'': Most of the ships are powered by solar sails, with the exception being the Ironclads, which are powered by dark matter. The sails on ships that have them can be targetted to cripple the ship's mobility. Ships with sails will also lose power if the ship moves into a [[{{Space Clouds}} Nebula]], as it obstructs light from nearby stars.
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[[folder:Webcomics]]
* ''Webcomic/SchlockMercenary'':
** The Gatekeepers use "solar sail material" to make Dyson Spheres, their word for which translates to "this was expensive to build."
** In one arc the crew encounter a small STL starship with a solar sail that "you could giftwrap planets with."
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