Solar sail
Solar sails (also known as lightsails, light sails, and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010.
This article is about spacecraft propulsion by radiation pressure from sunlight. For propulsion by means of the solar wind, see electric sail and magnetic sail. For The Planetary Society spacecraft, see LightSail.
A useful analogy to solar sailing may be a sailing boat; the light exerting a force on the large surface is akin to a sail being blown by the wind. High-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight, a concept known as beam sailing. Solar sail craft offer the possibility of low-cost operations combined with high speeds (relative to chemical rockets) and long operating lifetimes. Since they have few moving parts and use no propellant, they can potentially be used numerous times for the delivery of payloads.
Solar sails use a phenomenon that has a proven, measured effect on astrodynamics. Solar pressure affects all spacecraft, whether in interplanetary space or in orbit around a planet or small body. A typical spacecraft going to Mars, for example, will be displaced thousands of kilometers by solar pressure, so the effects must be accounted for in trajectory planning, which has been done since the time of the earliest interplanetary spacecraft of the 1960s. Solar pressure also affects the orientation of a spacecraft, a factor that must be included in spacecraft design.[1]
The total force exerted on an 800 by 800 metres (2,600 by 2,600 ft) solar sail, for example, is about 5 N (1.1 lbf) at Earth's distance from the Sun,[2] making it a low-thrust propulsion system, similar to spacecraft propelled by electric engines, but as it uses no propellant, that force is exerted almost constantly and the collective effect over time is great enough to be considered a potential manner of propelling spacecraft.
History of concept[edit]
Johannes Kepler observed that comet tails point away from the Sun and suggested that the Sun caused the effect. In a letter to Galileo in 1610, he wrote, "Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void."[3] He might have had the comet tail phenomenon in mind when he wrote those words, although his publications on comet tails came several years later.[4]
James Clerk Maxwell, in 1861–1864, published his theory of electromagnetic fields and radiation, which shows that light has momentum and thus can exert pressure on objects. Maxwell's equations provide the theoretical foundation for sailing with light pressure. So by 1864, the physics community and beyond knew sunlight carried momentum that would exert a pressure on objects.
Jules Verne, in From the Earth to the Moon,[5] published in 1865, wrote "there will some day appear velocities far greater than these [of the planets and the projectile], of which light or electricity will probably be the mechanical agent ... we shall one day travel to the moon, the planets, and the stars."[6] This is possibly the first published recognition that light could move ships through space.
Pyotr Lebedev was first to successfully demonstrate light pressure, which he did in 1899 with a torsional balance;[7] Ernest Nichols and Gordon Hull conducted a similar independent experiment in 1901 using a Nichols radiometer.[8]
Svante Arrhenius predicted in 1908 the possibility of solar radiation pressure distributing life spores across interstellar distances, providing one means to explain the concept of panspermia. He was apparently the first scientist to state that light could move objects between stars.[9]
Konstantin Tsiolkovsky first proposed using the pressure of sunlight to propel spacecraft through space and suggested, "using tremendous mirrors of very thin sheets to utilize the pressure of sunlight to attain cosmic velocities".[10]
Friedrich Zander (Tsander) published a technical paper in 1925 that included technical analysis of solar sailing. Zander wrote of "applying small forces" using "light pressure or transmission of light energy to distances by means of very thin mirrors".[11]
JBS Haldane speculated in 1927 about the invention of tubular spaceships that would take humanity to space and how "wings of metallic foil of a square kilometre or more in area are spread out to catch the Sun's radiation pressure".[12]
J. D. Bernal wrote in 1929, "A form of space sailing might be developed which used the repulsive effect of the Sun's rays instead of wind. A space vessel spreading its large, metallic wings, acres in extent, to the full, might be blown to the limit of Neptune's orbit. Then, to increase its speed, it would tack, close-hauled, down the gravitational field, spreading full sail again as it rushed past the Sun."[13]
Arthur C. Clarke wrote Sunjammer, a science fiction short story originally published in the March 1964 issue of Boys' Life [14] depicting a yacht race between solar sail spacecraft.
Carl Sagan, in the 1970s, popularized the idea of sailing on light using a giant structure which would reflect photons in one direction, creating momentum. He brought up his ideas in college lectures, books, and television shows. He was fixated on quickly launching this spacecraft in time to perform a rendezvous with Halley's Comet. Unfortunately, the mission didn't take place in time and he would never live to finally see it through.[15]
The first formal technology and design effort for a solar sail began in 1976 at Jet Propulsion Laboratory for a proposed mission to rendezvous with Halley's Comet.[2]
Types[edit]
Reflective[edit]
Most solar sails are based on reflection.[16] The surface of the sail is highly reflective, like a mirror, and light reflecting off of the surface imparts a force.
Projects operating or completed[edit]
Attitude (orientation) control[edit]
Both the Mariner 10 mission, which flew by the planets Mercury and Venus, and the MESSENGER mission to Mercury demonstrated the use of solar pressure as a method of attitude control in order to conserve attitude-control propellant.
Hayabusa also used solar pressure on its solar paddles as a method of attitude control to compensate for broken reaction wheels and chemical thruster.
MTSAT-1R (Multi-Functional Transport Satellite)'s solar sail counteracts the torque produced by sunlight pressure on the solar array. The trim tab on the solar array makes small adjustments to the torque balance.
Suborbital tests[edit]
Cosmos 1, a joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science attempted to launch a suborbital prototype vehicle in 2005, which was destroyed due to a rocket failure.
A 15-meter-diameter solar sail (SSP, solar sail sub payload, soraseiru sabupeiro-do) was launched together with ASTRO-F on a M-V rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely.[69]
On August 9, 2004, the Japanese ISAS successfully deployed two prototype solar sails from a sounding rocket. A clover-shaped sail was deployed at 122 km altitude and a fan-shaped sail was deployed at 169 km altitude. Both sails used 7.5-micrometer film. The experiment purely tested the deployment mechanisms, not propulsion.[70]
Projects still in development or unknown status[edit]
Gossamer deorbit sail[edit]
As of December 2013, the European Space Agency (ESA) has a proposed deorbit sail, named "Gossamer", that would be intended to be used to accelerate the deorbiting of small (less than 700 kilograms (1,500 lb)) artificial satellites from low Earth orbits. The launch mass is 2 kilograms (4.4 lb) with a launch volume of only 15×15×25 centimetres (0.49×0.49×0.82 ft). Once deployed, the sail would expand to 5 by 5 metres (16 ft × 16 ft) and would use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite reentry.[43]
In popular culture[edit]
Cordwainer Smith gives a description of solar-sail-powered spaceships in "The Lady Who Sailed The Soul", published first in April 1960.
Jack Vance wrote a short story about a training mission on a solar-sail-powered spaceship in "Sail 25", published in 1961.
Arthur C. Clarke and Poul Anderson (writing as Winston P. Sanders) independently published stories featuring solar sails, both stories titled "Sunjammer," in 1964. Clarke retitled his story "The Wind from the Sun" when it was reprinted, in order to avoid confusion.[118]
In Larry Niven and Jerry Pournelle's 1974 novel The Mote in God's Eye, aliens are discovered when their laser-sail propelled probe enters human space.
A similar technology was the theme in the Star Trek: Deep Space Nine episode "Explorers". In the episode, Lightships are described as an ancient technology used by Bajorans to travel beyond their solar system by using light from the Bajoran sun and specially constructed sails to propel them through space ("Explorers". Star Trek: Deep Space Nine. Season 3. Episode 22.).[119]
In the 2002 Star Wars film Attack of the Clones, the main villain Count Dooku was seen using a spacecraft with solar sails.[120]
In the 2009 film Avatar, the spacecraft which transports the protagonist Jake Sully to the Alpha Centauri system, the ISV Venture Star, uses solar sails as a means of propulsion to accelerate the vehicle away from the Earth towards Alpha Centauri.
In the third season of Apple TV+'s alternate history TV show For All Mankind, the fictional NASA spaceship Sojourner 1 utilises solar sails for additional propulsion on its way to Mars.
In the final episode of the first season of 2024 Netflix 2024 TV show, 3 Body Problem, one of the protagonists, Will Downing, has his cryogenically frozen brain launched into space toward the oncoming Trisolarian spaceship, using solar sails and nuclear pulse propulsion to accelerate it to a fraction of the speed of light.