View source for Physics:Solar sail

{{short description|Space propulsion method using Sun radiation}}

[[File:IKAROS solar sail.jpg|thumb|250px|IKAROS space-probe with solar sail in flight (artist's depiction) showing a typical square sail configuration]]

'''Solar sails''' (also known as '''lightsails''', '''light sails''', and '''photon sails''') are a method of [[Astronomy:Spacecraft propulsion|spacecraft propulsion]] using [[Astronomy:Radiation pressure|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 [[Engineering:IKAROS|IKAROS]], launched in 2010.

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 [[Engineering:Laser propulsion|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 [[Astronomy:Interplanetary spaceflight|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 [[Engineering:Spacecraft design|spacecraft design]].<ref>Georgevic, R. M. (1973) "The Solar Radiation Pressure Forces and Torques Model", ''The Journal of the Astronautical Sciences'', Vol. 27, No. 1, Jan–Feb. First known publication describing how solar radiation pressure creates forces and torques that affect spacecraft.</ref>

The total force exerted on an {{convert|800 by 800|m}} solar sail, for example, is about {{cvt|5|N|lbf|lk=on}} at Earth's distance from the Sun,<ref name="Wright ">{{citation| author = Jerome Wright| year = 1992| title = Space Sailing| publisher = Gordon and Breach Science Publishers}}</ref> making it a low-thrust [[Astronomy:Spacecraft propulsion|propulsion]] system, similar to spacecraft propelled by [[Engineering:Electrically powered spacecraft propulsion|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==
[[Biography:Johannes Kepler|Johannes Kepler]] observed that [[Astronomy:Comet|comet]] tails point away from the [[Astronomy:Sun|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."<ref>"Da naves aut vela coelesti aurae accommoda, eruntqui ne ab illa quidem vastitate sibi metuant." - ''Dissertatio cum Nuncio Sidereo''</ref> 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.<ref>Johannes Kepler (1604) ''Ad vitellionem parali pomena'', Frankfort; (1619) ''De cometis liballi tres '', Augsburg</ref>

[[Biography:James Clerk Maxwell|James Clerk Maxwell]], in 1861–1864, published his theory of [[Physics:Electromagnetic field|electromagnetic field]]s and radiation, which shows that light has [[Physics:Momentum|momentum]] and thus can exert pressure on objects. [[Physics:Maxwell's equations|Maxwell's equations]] provide the theoretical foundation for sailing with light pressure. So by 1864, the physics community and beyond knew [[Astronomy:Sunlight|sunlight]] carried momentum that would exert a pressure on objects.

Jules Verne, in ''From the Earth to the Moon'',<ref name="Verne1865">Jules Verne (1865) ''De la Terre à la Lune'' (''From the Earth to the Moon'')</ref> 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."<ref name="Impey">Chris Impey, ''Beyond: Our Future in Space,'' W. W. Norton & Company (2015)</ref> This is possibly the first published recognition that light could move ships through space.

[[Biography:Pyotr Lebedev|Pyotr Lebedev]] was first to successfully demonstrate light pressure, which he did in 1899 with a torsional balance;<ref>P. Lebedev, 1901, "Untersuchungen über die Druckkräfte des Lichtes", ''Annalen der Physik'', 1901</ref> Ernest Nichols and Gordon Hull conducted a similar independent experiment in 1901 using a [[Engineering:Nichols radiometer|Nichols radiometer]].<ref>{{cite web|url=http://dujs.dartmouth.edu/spring-2008-10th-anniversary-edition/what-else-has-happened-a-celebration-of-the-legacy-of-physics-at-dartmouth|title=A Celebration of the Legacy of Physics at Dartmouth |last=Lee|first=Dillon |year=2008|work=Dartmouth Undergraduate Journal of Science|publisher=Dartmouth College|access-date=2009-06-11}}</ref>

[[Biography:Svante Arrhenius|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 [[Biology:Panspermia|panspermia]]. He was apparently the first scientist to state that light could move objects between stars.<ref>Svante Arrhenius (1908) ''Worlds in the Making''</ref>

[[Biography:Konstantin Tsiolkovsky|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".<ref>Urbanczyk, Mgr., "Solar Sails-A Realistic Propulsion for Space Craft", Translation Branch Redstone Scientific Information Center Research and Development Directorate U.S. Army Missile Command Redstone Arsenal, Alabama, 1965.</ref>

[[Biography:Friedrich Zander|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".<ref>Friedrich Zander's 1925 paper, "Problems of flight by jet propulsion: interplanetary flights", was translated by NASA. See NASA Technical Translation F-147 (1964), p. 230.</ref>

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".<ref>JBS Haldane, ''The Last Judgement'', New York and London, Harper & Brothers, 1927.</ref>

[[Biography:J. D. Bernal|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."<ref>J. D. Bernal (1929) ''The World, the Flesh & the Devil: An Enquiry into the Future of the Three Enemies of the Rational Soul''</ref>

[[Biography:Arthur C. Clarke|Arthur C. Clarke]] wrote ''Sunjammer'', a science fiction short story originally published in the March 1964 issue of ''Boys' Life'' <ref name=Arthurcclarke>[http://www.arthurcclarke.net/?scifi=1&type=4 Short Stories] {{Webarchive|url=https://web.archive.org/web/20111002023436/http://www.arthurcclarke.net/?scifi=1&type=4 |date=2011-10-02 }}. ''Arthurcclarke.net'', 2007-2011, retrieved June 22, 2011</ref> depicting a yacht race between solar sail spacecraft. 

[[Biography:Carl Sagan|Carl Sagan]], in the 1970s, popularized the idea of sailing on light using a giant structure which would reflect [[Physics:Photons|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 [[Astronomy:Halley's Comet|Halley's Comet]]. Unfortunately, the mission didn't take place in time and he would never live to finally see it through.<ref>{{cite web | url=https://www.centauri-dreams.org/2017/05/05/remembering-the-sail-mission-to-halleys-comet/ | title=Remembering the Sail Mission to Halley's Comet | author=Paul Gilster |date=May 5, 2017}}</ref>

The first formal technology and design effort for a solar sail began in 1976 at [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] for a proposed mission to rendezvous with [[Astronomy:Halley's Comet|Halley's Comet]].<ref name="Wright " />

== Types ==
=== Reflective ===
Most solar sails are based on [[Physics:Reflection|reflection]].<ref name="nasa-popular">{{cite web |last1=Potter |first1=Sean |title=NASA-Supported Solar Sail Could Take Science to New Heights |url=https://www.nasa.gov/press-release/nasa-supported-solar-sail-could-take-science-to-new-heights |website=NASA |access-date=9 February 2023 |date=24 May 2022}}</ref> The surface of the sail is highly reflective, like a [[Physics:Mirror|mirror]], and light reflecting off of the surface imparts a force.

=== Diffractive ===
{{Main|Physics:Diffractive solar sail}}
In 2018, [[Physics:Diffraction|diffraction]] was proposed as a different solar sail propulsion mechanism, which is claimed to have several advantages.<ref>{{cite news |last1=Dvorsky |first1=George |title=NASA Moves Ahead With Wild Solar Sail Concept |url=https://gizmodo.com/nasa-solar-sail-diffractive-lightsails-1848971175 |access-date=25 May 2022 |work=Gizmodo |issue=25 May 2022 |language=en-us}}</ref><ref name="adv">{{cite web |last1=Hall |first1=Loura |title=Diffractive Solar Sailing |url=https://www.nasa.gov/directorates/spacetech/niac/2022/diffractive_solar_sailing/ |website=NASA |access-date=9 February 2023 |date=24 May 2022 |archive-date=9 February 2023 |archive-url=https://web.archive.org/web/20230209135439/https://www.nasa.gov/directorates/spacetech/niac/2022/diffractive_solar_sailing/ |url-status=dead }}</ref>

== Alternatives ==
=== Electric solar wind ===
{{main | Engineering:Electric sail }}

Pekka Janhunen from [[Organization:Finnish Meteorological Institute|FMI]] has  proposed a type of solar sail called the electric solar wind sail.<ref>{{cite web|url=http://www.space.fmi.fi/~pjanhune/Esail/|title=Solar Sails Could Send Spacecraft 'Sailing' Through Space|author=NASA}}</ref> Mechanically it has little in common with the traditional solar sail design. The sails are replaced with straightened conducting tethers (wires) placed [[Radius|radially]] around the host ship. The wires are electrically charged to create an [[Physics:Electric field|electric field]] around the wires. The electric field extends a few tens of metres into the plasma of the surrounding solar wind. The solar electrons are reflected by the electric field (like the photons on a traditional solar sail). The radius of the sail is from the electric field rather than the actual wire itself, making the sail lighter. The craft can also be steered by regulating the electric charge of the wires. A practical electric sail would have 50–100 straightened wires with a length of about 20&nbsp;km each.<ref>{{cite web |access-date= Jan 2, 2022 | url=https://www.electric-sailing.fi/ | title=Electric Solar Wind Sail (E-sail)}}</ref>

Electric solar wind sails can adjust their electrostatic fields and sail attitudes.

=== Magnetic ===
{{main | Physics:Magnetic sail }}

A [[Physics:Magnetic sail|magnetic sail]] would also employ the solar wind. However, the magnetic field deflects the electrically charged particles in the wind. It uses wire loops, and runs a static current through them instead of applying a static voltage.<ref>{{cite web|url=http://www.niac.usra.edu/files/library/meetings/fellows/nov99/320Zubrin.pdf |title=Fellows meeting |date=1999 |website=www.niac.usra.edu/files }}</ref>

All these designs maneuver, though the mechanisms are different.

Magnetic sails bend the path of the charged protons that are in the [[Astronomy:Solar wind|solar wind]]. By changing the sails' attitudes, and the size of the magnetic fields, they can change the amount and direction of the thrust.

==Physical principles for reflective sails==

===Solar radiation pressure===
{{Main|Astronomy:Radiation pressure}}
The force imparted to a solar sail arises from the momentum of photons. The momentum of a [[Physics:Photon|photon]] or an entire flux is given by [[Physics:Energy–momentum relation|Einstein's relation]]:<ref>{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html |title=Relativistic Momentum |publisher=Hyperphysics.phy-astr.gsu.edu |access-date=2015-02-02}}</ref><ref name="wright-appendixA">Wright, Appendix A</ref>

:<math>p = E/c</math>

where p is the momentum, E is the energy (of the photon or flux), and c is the [[Physics:Speed of light|speed of light]]. Specifically, the momentum of a photon depends on its wavelength {{math|''p'' {{=}} ''h/λ''}}

Solar radiation pressure can be related to the irradiance ([[Astronomy:Solar constant|solar constant]]) value of 1361&nbsp;W/m<sup>2</sup> at 1&nbsp;[[Astronomy:Astronomical unit|AU]] (Earth-Sun distance), as revised in 2011:<ref>{{cite journal|author1=Kopp, G. |author2=Lean, J. L. |title=A new, lower value of total solar irradiance: Evidence and climate significance|journal=Geophysical Research Letters |volume=38 |issue=1 |year=2011|pages=n/a |doi=10.1029/2010GL045777|bibcode=2011GeoRL..38.1706K |doi-access=free }}</ref><!--DO NOT CHANGE FROM SIG FIGURES: LEADS TO MISLEADING VALUES & INCONSISTENCIES-->

*perfect absorbance: F = 4.54&nbsp;μN per square metre (4.54&nbsp;μ[[Pascal (unit)|Pa]]) in the direction of the incident beam (a [[Physics:Inelastic collision|perfectly inelastic collision]])
*perfect reflectance: F = 9.08&nbsp;μN per square metre (9.08&nbsp;μPa) in the direction normal to surface (an [[Physics:Elastic collision|elastic collision]])

An ideal sail is flat and has 100% [[Physics:Specular reflection|specular reflection]]. An actual sail will have an overall efficiency of about 90%, about 8.17&nbsp;μN/m<sup>2</sup>,<ref name="wright-appendixA"/> due to curvature (billow), wrinkles, absorbance, re-radiation from front and back, non-specular effects, and other factors.
[[File:Sail-Force1.gif|thumb|Force on a sail results from reflecting the photon flux]]
The force on a sail and the actual acceleration of the craft vary by the inverse square of distance from the Sun (unless extremely close to the Sun<ref>McInnes, C. R. and Brown, J. C. (1989) ''Solar Sail Dynamics with an Extended Source of Radiation Pressure'', [[Organization:International Astronautical Federation|International Astronautical Federation]], IAF-89-350, October.</ref>), and by the square of the cosine of the angle between the sail force vector and the radial from the Sun, so

:<math>F = F_0 \cos^2(\theta) / R^2</math> (for an ideal sail)

where R is distance from the Sun in AU. An actual square sail can be modelled as:

:<math>F = F_0 (0.349 + 0.662 \cos( 2\theta) - 0.011 \cos( 4\theta)) / R^2</math>

Note that the force and acceleration approach zero generally around θ = 60° rather than 90° as one might expect with an ideal sail.<ref>Wright, Appendix B.</ref>

If some of the energy is absorbed, the absorbed energy will heat the sail, which re-radiates that energy from the front and rear surfaces, depending on the [[Physics:Emissivity|emissivity]] of those two surfaces.

[[Astronomy:Solar wind|Solar wind]], the flux of charged particles blown out from the Sun, exerts a nominal dynamic pressure of about 3 to 4 [[Pascal (unit)|nPa]], three orders of magnitude less than solar radiation pressure on a reflective sail.<ref>{{Cite web|url=http://www.swpc.noaa.gov/SWN/index.html|archive-url=https://web.archive.org/web/20141127142813/http://www.swpc.noaa.gov/SWN/index.html|url-status=dead|title=NOAA / Space Weather Prediction Center|archive-date=November 27, 2014}}</ref>

===Sail parameters===
Sail loading (areal density) is an important parameter, which is the total mass divided by the sail area, expressed in g/m<sup>2</sup>. It is represented by the Greek letter σ (sigma).

A sail craft has a characteristic acceleration, a<sub>c</sub>, which it would experience at 1&nbsp;AU when facing the Sun. Note this value accounts for both the incident and reflected momentums. Using the value from above of 9.08 μN per square metre of radiation pressure at 1 AU, a<sub>c</sub> is related to areal density by:

:a<sub>c</sub> = 9.08(efficiency) / σ mm/s<sup>2</sup>

Assuming 90% efficiency, a<sub>c</sub> =  8.17 / σ mm/s<sup>2</sup>

The lightness number, λ, is the dimensionless ratio of maximum vehicle acceleration divided by the Sun's local gravity.  Using the values at 1&nbsp;AU:

:λ = a<sub>c</sub> / 5.93

The lightness number is also independent of distance from the Sun because both gravity and light pressure fall off as the inverse square of the distance from the Sun. Therefore, this number defines the types of orbit maneuvers that are possible for a given vessel.

The table presents some example values. Payloads are not included. The first two are from the detailed design effort at JPL in the 1970s. The third, the lattice sailer, might represent about the best possible performance level.<ref name="Wright " />  The dimensions for square and lattice sails are edges.  The dimension for heliogyro is blade tip to blade tip.

{| class="wikitable" style="text-align: center;"
|-
!Type
!σ (g/m<sup>2</sup>)
!a<sub>c</sub> (mm/s<sup>2</sup>)
!λ
!Size (km<sup>2</sup>)
|-
|Square sail
|5.27
|1.56
|0.26
|0.820
|-
|Heliogyro
|6.39
|1.29
|0.22
|15
|-
|Lattice&nbsp;sailer
|0.07
|117
|20
|0.840
|}

===Attitude control===
An active [[Astronomy:Spacecraft attitude control|attitude control]] system (ACS) is essential for a sail craft to achieve and maintain a desired orientation. The required sail orientation changes slowly (often less than 1 degree per day) in interplanetary space, but much more rapidly in a planetary orbit. The ACS must be capable of meeting these orientation requirements. Attitude control is achieved by a relative shift between the craft's [[Center of pressure (fluid mechanics)|center of pressure]] and its [[Physics:Center of mass|center of mass]]. This can be achieved with control vanes, movement of individual sails, movement of a control mass, or altering reflectivity.

Holding a constant attitude requires that the ACS maintain a net torque of zero on the craft. The total force and torque on a sail, or set of sails, is not constant along a trajectory. The force changes with solar distance and sail angle, which changes the billow in the sail and deflects some elements of the supporting structure, resulting in changes in the sail force and torque.

Sail temperature also changes with solar distance and sail angle, which changes sail dimensions. The radiant heat from the sail changes the temperature of the supporting structure. Both factors affect total force and torque.

To hold the desired attitude the ACS must compensate for all of these changes.<ref name="wright 6+B">Wright, ibid., Ch 6 and Appendix B.</ref>

===Constraints===
In Earth orbit, solar pressure and drag pressure are typically equal at an altitude of about 800&nbsp;km, which means that a sail craft would have to operate above that altitude. Sail craft must operate in orbits where their turn rates are compatible with the orbits, which is generally a concern only for spinning disk configurations.

Sail operating temperatures are a function of solar distance, sail angle, reflectivity, and front and back emissivities. A sail can be used only where its temperature is kept within its material limits. Generally, a sail can be used rather close to the Sun, around 0.25&nbsp;AU, or even closer if carefully designed for those conditions.<ref name="Wright " />

==Applications==
Potential applications for sail craft range throughout the [[Astronomy:Solar System|Solar System]], from near the Sun to the comet clouds beyond Neptune.  The craft can make outbound voyages to deliver loads or to take up station keeping at the destination.  They can be used to haul cargo and possibly also used for human travel.<ref name="Wright " />

===Inner planets===
For trips within the inner Solar System, they can deliver payloads and then return to Earth for subsequent voyages, operating as an interplanetary shuttle.  For Mars in particular, the craft could provide economical means of routinely supplying operations on the planet according to Jerome Wright, "The cost of launching the necessary conventional propellants from Earth are enormous for manned missions. Use of sailing ships could potentially save more than $10 billion in mission costs."<ref name="Wright "/>

Solar sail craft can approach the Sun to deliver observation payloads or to take up station keeping orbits.  They can operate at 0.25 AU or closer.  They can reach high orbital inclinations, including polar.

Solar sails can travel to and from all of the inner planets.  Trips to Mercury and Venus are for rendezvous and orbit entry for the payload.  Trips to Mars could be either for rendezvous or swing-by with release of the payload for [[Astronomy:Aerobraking|aerodynamic braking]].<ref name="Wright " />

{|class=wikitable style="text-align:right"
|-
!rowspan=2|Sail size<br/>m!!colspan=2|Mercury Rendezvous!!colspan=2|Venus Rendezvous!!colspan=2|Mars Rendezvous!!colspan=2|Mars Aerobrake
|-
!days!!tons!!days!!tons!!days!!tons!!days!!tons
|-
|rowspan=3|800<br/>σ = 5 g/m<sup>2</sup><br/>w/o cargo
|600||9||200||1||400||2||131||2
|-
|900||19||270||5||500||5||200||5
|-
|1200||28|| || ||700||9||338||10
|-
|rowspan=3|2000<br/>σ = 3 g/m<sup>2</sup><br/>w/o cargo
|600||66||200||17||400||23||131||20
|-
|900||124||270||36||500||40||200||40
|-
|1200||184|| || ||700||66||338||70
|}

===Outer planets===
Minimum transfer times to the outer planets benefit from using an indirect transfer (solar swing-by).  However, this method results in high arrival speeds.  Slower transfers have lower arrival speeds.

The minimum transfer time to Jupiter for ''a<sub>c</sub>'' of 1&nbsp;mm/s<sup>2</sup> with no departure velocity relative to Earth is 2 years when using an indirect transfer (solar swing-by).  The arrival speed (''V''<span style="font-size:140%;"><sub>∞</sub></span>) is close to 17&nbsp;km/s.  For Saturn, the minimum trip time is 3.3 years, with an arrival speed of nearly 19&nbsp;km/s.<ref name="Wright " />

{| class="wikitable" style="text-align: center; width: 300px; height: 120px;"
|+ Minimum times to the outer planets (''a<sub>c</sub>'' = 1&nbsp;mm/s<sup>2</sup>)
|-
!&nbsp;
!&nbsp;&nbsp;Jupiter&nbsp;&nbsp;
!&nbsp;&nbsp;Saturn&nbsp;&nbsp;
!&nbsp;&nbsp;Uranus&nbsp;&nbsp;
!&nbsp;&nbsp;Neptune&nbsp;&nbsp;
|-
|Time, yr
|2.0
|3.3
|5.8
|8.5
|-
|Speed, km/s
|17
|19
|20
|20
|}

=== Oort Cloud/Sun's inner gravity focus ===

The Sun's inner [[Astronomy:Solar gravitational lens|gravitational focus]] point lies at minimum distance of 550 AU from the Sun, and is the point to which light from distant objects is [[Physics:Two-body problem in general relativity#Bending of light by gravity|focused by gravity]] as a result of it passing by the Sun. This is thus the distant point to which solar gravity will cause the region of deep space on the other side of the Sun to be focused, thus serving effectively as a very large telescope objective lens.<ref>Eshleman, Von R., "Gravitational lens of the Sun: its potential for observations and communications over interstellar distances," ''Science, Vol. 205'', No. 4411 (1979) pp. 1133-1135. {{doi|10.1126/science.205.4411.1133}}</ref><ref name=lens>{{cite web|last1=Maccone |first1=Claudio |title=The Sun as a Gravitational Lens : A Target for Space Missions A Target for Space Missions Reaching 550 AU to 1000 AU |url=http://www.spaceroutes.com/astrocon/AstroconVTalks/Maccone-AstroconV.pdf |archive-url=https://web.archive.org/web/20100715033119/http://www.spaceroutes.com/astrocon/AstroconVTalks/Maccone-AstroconV.pdf |url-status=dead |archive-date=15 July 2010 |access-date=29 October 2014 }}</ref>

It has been proposed that an inflated sail, made of [[Chemistry:Beryllium|beryllium]], that starts at 0.05 AU from the Sun would gain an initial acceleration of 36.4&nbsp;m/s<sup>2</sup>, and reach a speed of 0.00264c (about 950&nbsp;km/s) in less than a day. Such proximity to the Sun could prove to be impractical in the near term due to the structural degradation of beryllium at high temperatures, diffusion of hydrogen at high temperatures as well as an electrostatic gradient, generated by the ionization of beryllium from the solar wind, posing a burst risk. A revised perihelion of 0.1 AU would reduce the aforementioned temperature and solar flux exposure.<ref>{{cite web|author=Paul Gilster |url=http://www.centauri-dreams.org/?p=4238 |title=An Inflatable Sail to the Oort Cloud |publisher=Centauri-dreams.org |date=2008-11-12 |access-date=2015-02-02}}</ref>
Such a sail would take "Two and a half years to reach the heliopause, six and a half years to reach the Sun’s inner [[Physics:Gravitational focusing|gravitational focus]], with arrival at the inner Oort Cloud in no more than thirty years."<ref name=lens/> "Such a mission could perform useful astrophysical observations en route, explore gravitational focusing techniques, and image Oort Cloud objects while exploring particles and fields in that region that are of galactic rather than solar origin."

===Satellites===
[[Biography:Robert L. Forward|Robert L. Forward]] has commented that a solar sail could be used to modify the orbit of a satellite about the Earth. In the limit, a sail could be used to "hover" a satellite above one pole of the Earth. Spacecraft fitted with solar sails could also be placed in close orbits such that they are stationary with respect to either the Sun or the Earth, a type of satellite named by Forward a "[[Astronomy:Statite|statite]]". This is possible because the propulsion provided by the sail offsets the gravitational attraction of the Sun. Such an orbit could be useful for studying the properties of the Sun for long durations.<ref name=ESA/> Likewise a solar sail-equipped spacecraft could also remain on station nearly above the polar [[Astronomy:Terminator (solar)|solar terminator]] of a planet such as the Earth by tilting the sail at the appropriate angle needed to counteract the planet's gravity.<ref name=ESA>{{cite journal | journal= ESA Bulletin |volume=98 | date=1999 | title=Solar Sails for Space Exploration – The Development and Demonstration of Critical Technologies in Partnership |author=M. Leipold, D. Kassing, M. Eiden, L. Herbeck | url=https://www.esa.int/esapub/bulletin/bullet98/LEIPOLD.pdf}}</ref>

In his book ''[[Astronomy:The Case for Mars|The Case for Mars]]'', [[Biography:Robert Zubrin|Robert Zubrin]] points out that the reflected sunlight from a large statite, placed near the polar terminator of the planet Mars, could be focused on one of the Martian polar ice caps to significantly warm the planet's atmosphere. Such a statite could be made from asteroid material.

A group of satellites designed to act as sails has been proposed to measure Earth's Energy Imbalance which is the most fundamental measure of the planet's rate of [[Earth:Global warming|global warming]]. On-board state-of-the-art [[Physics:Accelerometer|accelerometer]]s would measure shifts in the pressure differential between incoming solar and outgoing [[Physics:Thermal radiation|thermal radiation]] on opposing sides of each satellite.   Measurement accuracy has been projected to be better than that achievable with compact [[Astronomy:Radiometry|radiometric]] detectors.<ref>{{cite journal |last1=Hakuba |first1=Maria Z. |last2=Stephens |first2=Graeme L. |last3=Christophe |first3=Bruno |last4=Nash |first4=Alfred E. |last5=Foulon |first5=Bernard |display-authors=et al |title=Earth's Energy Imbalance Measured From Space |journal=IEEE Transactions on Geoscience and Remote Sensing |year=2019 |volume=57 |issue=1 |pages=32–45 |doi=10.1109/TGRS.2018.2851976|bibcode=2019ITGRS..57...32H |s2cid=57192349 |url=https://hal.archives-ouvertes.fr/hal-01870008/file/DFIE17094.1535440400_postprint.pdf }}</ref>

===Trajectory corrections===
The [[Astronomy:MESSENGER|MESSENGER]] probe orbiting [[Astronomy:Mercury (planet)|Mercury]] used light pressure on its solar panels to perform fine trajectory corrections on the way to Mercury.<ref>{{cite web|url=http://messenger.jhuapl.edu/news_room/details.php?id=102 |archive-url=https://web.archive.org/web/20130514095117/http://messenger.jhuapl.edu/news_room/details.php?id=102 |url-status=dead |archive-date=2013-05-14 |title=MESSENGER Sails on Sun's Fire for Second Flyby of Mercury |date=2008-09-05 |quote=On September 4, the MESSENGER team announced that it would not need to implement a scheduled maneuver to adjust the probe's trajectory. This is the fourth time this year that such a maneuver has been called off. The reason? A recently implemented navigational technique that makes use of solar-radiation pressure (SRP) to guide the probe has been extremely successful at maintaining MESSENGER on a trajectory that will carry it over the cratered surface of Mercury for a second time on October 6.}}</ref> By changing the angle of the solar panels relative to the Sun, the amount of solar radiation pressure was varied to adjust the spacecraft trajectory more delicately than possible with thrusters. Minor errors are greatly amplified by [[Astronomy:Gravity assist|gravity assist]] maneuvers, so using radiation pressure to make very small corrections saved large amounts of propellant.

===Interstellar flight===
In the 1970s, Robert Forward proposed two [[Astronomy:Beam-powered propulsion|beam-powered propulsion]] schemes using either lasers or [[Physics:Maser|maser]]s to push giant sails to a significant fraction of the [[Physics:Speed of light|speed of light]].<ref name="Forward1984RoundtripInterstellar">{{Cite journal| author=Forward, R.L. | title=Roundtrip Interstellar Travel Using Laser-Pushed Lightsails | journal=J Spacecraft | volume=21 | issue=2 | pages=187–195 | year=1984 | doi=10.2514/3.8632 |bibcode = 1984JSpRo..21..187F }}</ref>

In the science fiction novel ''Rocheworld'', Forward described a light sail propelled by super lasers. As the starship neared its destination, the outer portion of the sail would detach. The outer sail would then refocus and reflect the lasers back onto a smaller, inner sail. This would provide braking thrust to stop the ship in the destination star system.

Both methods pose monumental engineering challenges. The lasers would have to operate for years continuously at [[Gigawatt|gigawatt]] strength. Forward's solution to this requires enormous solar panel arrays to be built at or near the planet Mercury. A planet-sized mirror or [[Physics:Fresnel lens|Fresnel lens]] would need to be located at several dozen [[Astronomy:Astronomical unit|astronomical unit]]s from the Sun to keep the lasers focused on the sail. The giant braking sail would have to act as a precision mirror to focus the braking beam onto the inner "deceleration" sail.

A potentially easier approach would be to use a maser to drive a "solar sail" composed of a mesh of wires with the same spacing as the wavelength of the microwaves directed at the sail, since the manipulation of microwave radiation is somewhat easier than the manipulation of visible light. The hypothetical "[[Physics:Starwisp|Starwisp]]" interstellar probe design<ref name=starwisp>Forward, Robert L., "Starwisp: An Ultralight Interstellar Probe,” ''J. Spacecraft and Rockets, Vol. 22'', May–June 1985, pp. 345-350.</ref><ref name=starwisp2>Landis, Geoffrey A., "Microwave Pushed Interstellar Sail: Starwisp Revisited," paper AIAA-2000-3337, 36th Joint Propulsion Conference, Huntsville AL, July 17–19, 2000.</ref> would use microwaves, rather than visible light, to push it. Masers spread out more rapidly than optical lasers owing to their longer wavelength, and so would not have as great an effective range.

Masers could also be used to power a painted solar sail, a conventional sail coated with a layer of chemicals designed to evaporate when struck by microwave radiation.<ref>{{cite web|url=http://www.space.com/businesstechnology/technology/technovel_sail_050211.html |title=Earth To Mars in a Month With Painted Solar Sail |publisher=SPACE.com |date=2005-02-11 |access-date=2011-01-18}}</ref> The momentum generated by this [[Physics:Evaporation|evaporation]] could significantly increase the [[Thrust|thrust]] generated by solar sails, as a form of lightweight ablative laser propulsion.

To further focus the energy on a distant solar sail, Forward proposed a lens designed as a large [[Physics:Zone plate|zone plate]]. This would be placed at a location between the laser or maser and the spacecraft.<ref name="Forward1984RoundtripInterstellar" />

Another more physically realistic approach would be to use the light from the Sun to accelerate the spacecraft.<ref>"Solar Sail Starships:Clipper Ships of the Galaxy," chapter 6, Eugene F. Mallove and Gregory L. Matloff, ''The Starflight Handbook: A Pioneer's Guide to Interstellar Travel'', pp. 89-106, John Wiley & Sons, 1989. {{ISBN|978-0471619123}}</ref> The ship would first drop into an orbit making a close pass to the Sun, to maximize the solar energy input on the sail, then it would begin to accelerate away from the system using the light from the Sun. Acceleration will drop approximately as the inverse square of the distance from the Sun, and beyond some distance, the ship would no longer receive enough light to accelerate it significantly, but would maintain the final velocity attained. When nearing the target star, the ship could turn its sails toward it and begin to use the outward pressure of the destination star to decelerate. Rockets could augment the solar thrust.

Similar solar sailing launch and capture were suggested for [[Unsolved:Directed panspermia|directed panspermia]] to expand life in other solar systems. Velocities of 0.05% the speed of light could be obtained by solar sails carrying 10&nbsp;kg payloads, using thin solar sail vehicles with effective areal densities of 0.1&nbsp;g/m<sup>2</sup> with thin sails of 0.1&nbsp;[[Micrometre|µm]] thickness and sizes on the order of one square kilometer. Alternatively, swarms of 1&nbsp;mm capsules could be launched on solar sails with radii of 42&nbsp;cm, each carrying 10,000 capsules of a hundred million [[Earth:Extremophile|extremophile]] microorganisms to seed life in diverse target environments.<ref>{{Cite journal|last1=Meot-Ner (Mautner) |first1=Michael N. |last2=Matloff |first2=Gregory L. |title=Directed panspermia: A technical and ethical evaluation of seeding nearby solar systems |journal=Journal of the British Interplanetary Society |year=1979 |volume=32 |pages=419–423 |url=http://www.astro-ecology.com/PDFDirectedPanspermia1JBIS1997Paper.pdf |bibcode=1979JBIS...32..419M }}{{Dead link|date=June 2016|bot=medic}}{{cbignore|bot=medic}}</ref><ref>{{Cite journal|last = Mautner |first = Michael N. | title = Directed panspermia. 2. Technological advances toward seeding other solar systems, and the foundations of panbiotic ethics | journal = Journal of the British Interplanetary Society | year = 1995 | volume = 48 | pages = 435–440 }}</ref>

Theoretical studies suggest relativistic speeds if the solar sail harnesses a supernova.<ref>{{cite news |last1=Loeb |first1=Abraham |title=Surfing a Supernova |url=https://blogs.scientificamerican.com/observations/surfing-a-supernova/ |access-date=14 February 2020 |work=Scientific American Blogs |date=3 February 2019}}</ref>

===Deorbiting artificial satellites===
Small solar sails have been proposed to accelerate the deorbiting of small artificial satellites from Earth orbits.  Satellites in [[Astronomy:Low Earth orbit|low Earth orbit]] can use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite [[Astronomy:Atmospheric entry|reentry]].<ref name=ps20131226/>  A de-orbit sail developed at [[Organization:Cranfield University|Cranfield University]] is part of the UK satellite TechDemoSat-1, launched in 2014. The sail deployed at the end of the satellite's five-year useful life in May 2019.<ref>{{cite web|title = TechDemoSat-1 on-board camera captures drag sail deployment|url = https://www.sstl.co.uk/media-hub/latest-news/2019/techdemosat-1-on-board-camera-captures-drag-sail-deployment|access-date = 2022-11-10}}</ref> The sail's purpose is to bring the satellite out of orbit over a period of about 25 years.<ref>[https://interact.innovateuk.org/-/22-295-864-amazing-things-you-need-to-know-about-the-uk-s-newest-satellite "22,295,864 amazing things you need to know about the UK’s newest satellite"] {{Webarchive|url=https://web.archive.org/web/20151208152650/https://interact.innovateuk.org/-/22-295-864-amazing-things-you-need-to-know-about-the-uk-s-newest-satellite |date=2015-12-08 }}. ''Innovate UK''.</ref> In July 2015 British 3U [[Engineering:CubeSat|CubeSat]] called DeorbitSail was launched into space with the purpose of testing 16 m<sup>2</sup> deorbit structure,<ref>{{cite web|title = Mission|url = http://www.surrey.ac.uk/ssc/research/space_vehicle_control/deorbitsail/mission/index.htm|website = www.surrey.ac.uk|access-date = 2016-01-30|archive-date = 2016-03-04|archive-url = https://web.archive.org/web/20160304103911/http://www.surrey.ac.uk/ssc/research/space_vehicle_control/deorbitsail/mission/index.htm|url-status = dead}}</ref> but eventually it failed to deploy it.<ref>{{cite web|title = DeorbitSail Update and Initial Camera Image|url = http://amsat-uk.org/2015/11/13/deorbitsail-update-and-initial-camera-image/|website = AMSAT-UK|access-date = 2016-01-30|date = 2015-11-13}}</ref> A student 2U CubeSat mission called [[Engineering:PW-Sat2|PW-Sat2]], launched in December 2018 and tested a 4 m<sup>2</sup> deorbit sail. It successfully deorbited in February 2021.<ref>{{cite web|title = PW-Sat2 gets 180 000 € to fund the launch|url = http://pw-sat.pl/en/2016/01/pw-sat2-gets-180-000-e/|archive-url = https://web.archive.org/web/20160131013601/http://pw-sat.pl/en/2016/01/pw-sat2-gets-180-000-e/|url-status = dead|archive-date = 2016-01-31|website = PW-Sat2: Polish student satellite project|access-date = 2016-01-30|language = en-GB}}</ref> In June 2017, a second British 3U [[Engineering:CubeSat|CubeSat]] called InflateSail deployed a 10 m<sup>2</sup> deorbit sail at an altitude of {{convert|500|km|mi|sp=us}}.<ref name="UoS2017">{{cite web|title=Surrey Space Centre celebrates successful operation of InflateSail satellite|url=https://www.surrey.ac.uk/mediacentre/press/2017/surrey-space-centre-celebrates-successful-operation-inflatesail-satellite|website=surrey.ac.uk|access-date=15 July 2017}}</ref>
In June 2017 the 3U Cubesat URSAMAIOR has been launched in [[Astronomy:Low Earth orbit|low Earth orbit]] to test the deorbiting system ARTICA developed by Spacemind.<ref>{{cite web|title = URSA MAIOR (QB50 IT02)|url = http://space.skyrocket.de/doc_sdat/ursa-maior.htm|access-date = 2018-07-04}}</ref>  The device, which occupies only 0.4 U of the cubesat, shall deploy a sail of 2.1 m<sup>2</sup> to deorbit the satellite at the end of the operational life.<ref>{{cite web|title = ARTICA Spacemind|url = https://www.npcspacemind.com/in-space-now/|access-date = 2018-07-04}}</ref>

==Sail configurations==
[[File:Solarsail msfc.jpg|left|thumb|NASA illustration of the unlit side of a half-kilometre solar sail, showing the struts stretching the sail.]]
[[File:Cosmos1 in orbit.jpg|thumb|left|250px|An artist's depiction of a Cosmos&nbsp;1-type spaceship in orbit]]

[[Engineering:IKAROS|IKAROS]], launched in 2010, was the first practical solar sail vehicle.  As of 2015, it was still under thrust, proving the practicality of a solar sail for long-duration missions.<ref>{{cite web | url=http://www.jaxa.jp/press/2012/03/20120321_sac_ikaros.pdf | title=Small Solar Power Sail Demonstrator machine (小型ソーラー電力セイル実証機) | publisher=JAXA | access-date=24 March 2014}}</ref>  It is spin-deployed, with tip-masses in the corners of its square sail.  The sail is made of thin [[Chemistry:Polyimide|polyimide]] film, coated with evaporated aluminium.  It steers with electrically controlled [[Physics:Liquid crystal|liquid crystal]] panels.  The sail slowly spins, and these panels turn on and off to control the attitude of the vehicle.  When on, they diffuse light, reducing the momentum transfer to that part of the sail.  When off, the sail reflects more light, transferring more momentum.  In that way, they turn the sail.<ref>{{cite web|last=JAXA|title=Small Solar Power Sail Demonstrator 'IKAROS' Successful Attitude Control by Liquid Crystal Device|url=http://www.jaxa.jp/press/2010/07/20100723_ikaros_e.html|publisher=JAXA|access-date=24 March 2014}}</ref>  Thin-film [[Physics:Solar cell|solar cell]]s are also integrated into the sail, powering the spacecraft.  The design is very reliable, because spin deployment, which is preferable for large sails, simplified the mechanisms to unfold the sail and the LCD panels have no moving parts.

Parachutes have very low mass, but a parachute is not a workable configuration for a solar sail. Analysis shows that a parachute configuration would collapse from the forces exerted by shroud lines, since radiation pressure does not behave like aerodynamic pressure, and would not act to keep the parachute open.<ref>Wright, ibid., p. 71, last paragraph</ref>

The highest thrust-to-mass designs for ground-assembled deploy-able structures are square sails with the masts and [[Engineering:Guy (sailing)|guy]] lines on the dark side of the sail. Usually there are four masts that spread the corners of the sail, and a mast in the center to hold guy-wires. One of the largest advantages is that there are no hot spots in the rigging from wrinkling or bagging, and the sail protects the structure from the Sun. This form can, therefore, go close to the Sun for maximum thrust. Most designs steer with small moving sails on the ends of the spars.<ref name=jpl>{{cite web|url=http://solarsails.jpl.nasa.gov/introduction/design-construction.html |title=Design & Construction|publisher=NASA JPL |url-status=dead |archive-url = https://web.archive.org/web/20050311004606/http://solarsails.jpl.nasa.gov/introduction/design-construction.html |archive-date = 2005-03-11}}</ref>

[[File:sail-design-types.gif|center]]

In the 1970s [[Organization:JPL|JPL]] studied many rotating blade and ring sails for a mission to rendezvous with [[Astronomy:Halley's Comet|Halley's Comet]]. The intention was to stiffen the structures using angular momentum, eliminating the need for struts, and saving mass. In all cases, surprisingly large amounts of tensile strength were needed to cope with dynamic loads. Weaker sails would ripple or oscillate when the sail's attitude changed, and the oscillations would add and cause structural failure. The difference in the thrust-to-mass ratio between practical designs was almost nil, and the static designs were easier to control.<ref name=jpl />

JPL's reference design was called the "heliogyro". It had plastic-film blades deployed from rollers and held out by centrifugal forces as it rotated. The spacecraft's attitude and direction were to be completely controlled by changing the angle of the blades in various ways, similar to the cyclic and collective pitch of a [[Engineering:Helicopter|helicopter]]. Although the design had no mass advantage over a square sail, it remained attractive because the method of deploying the sail was simpler than a strut-based design.<ref name=jpl /> The [[Engineering:CubeSail (UltraSail)|CubeSail (UltraSail)]] is an active project aiming to deploy a heliogyro sail.

Heliogyro design is similar to the blades on a helicopter. The design is faster to manufacture due to lightweight centrifugal stiffening of sails. Also, they are highly efficient in cost and velocity because the blades are lightweight and long. Unlike the square and spinning disk designs, heliogyro is easier to deploy because the blades are compacted on a reel. The blades roll out when they are deploying after the ejection from the spacecraft. As the heliogyro travels through space the system spins around because of the centrifugal acceleration. Finally, payloads for the space flights are placed in the center of gravity to even out the distribution of weight to ensure stable flight.<ref name=jpl />

JPL also investigated "ring sails" (Spinning Disk Sail in the above diagram), panels attached to the edge of a rotating spacecraft. The panels would have slight gaps, about one to five percent of the total area. Lines would connect the edge of one sail to the other. Masses in the middles of these lines would pull the sails taut against the coning caused by the radiation pressure. JPL researchers said that this might be an attractive sail design for large crewed structures. The inner ring, in particular, might be made to have artificial gravity roughly equal to the gravity on the surface of Mars.<ref name=jpl />

A solar sail can serve a dual function as a high-gain antenna.<ref name=ant>{{cite web|first1=B.|last1=Khayatian|first2=Y.|last2=Rahmat-Samii|first3=R.|last3=Pogorzelski|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/12275/1/01-0276.pdf|archive-url=https://web.archive.org/web/20100527065541/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/12275/1/01-0276.pdf|url-status=dead|archive-date=2010-05-27|title=An Antenna Concept Integrated with Future Solar Sails}}</ref> Designs differ, but most modify the [[Engineering:Metallizing|metalization]] pattern to create a holographic monochromatic lens or mirror in the radio frequencies of interest, including visible light.<ref name=ant />

==Reflective sail making==
[[File:Solar sail material.jpg|thumb|Proposed material for the construction of solar sails - carbon fiber.]]

===Materials===

The most common material in current designs is a thin layer of aluminum coating on a polymer (plastic) sheet, such as aluminized 2&nbsp;µm [[Chemistry:Kapton|Kapton]] film. The polymer provides mechanical support as well as flexibility, while the thin metal layer provides the reflectivity.  Such material resists the heat of a pass close to the Sun and still remains reasonably strong. The aluminum reflecting film is on the Sun side. The sails of ''[[Engineering:Cosmos 1|Cosmos 1]]'' were made of aluminized PET film (Mylar).

Eric Drexler developed a concept for a sail in which the polymer was removed.<ref name=Drexler>{{cite web|url=http://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741.pdf?sequence=1|archive-url=https://web.archive.org/web/20110604235745/http://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741.pdf?sequence=1|url-status=dead|archive-date=2011-06-04|author=Drexler, K. E.|year=1977|title=Design of a High Performance Solar Sail System, MS Thesis |publisher=Dept. of Aeronautics and Astronautics, Massachusetts Institute of Techniology, Boston}}</ref> He proposed very high thrust-to-mass solar sails, and made prototypes of the sail material. His sail would use panels of thin aluminium film (30 to 100 [[Nanometre|nanometre]]s thick) supported by a [[Physics:Tension|tensile]] structure. The sail would rotate and would have to be continually under thrust. He made and handled samples of the film in the laboratory, but the material was too delicate to survive folding, launch, and deployment. The design planned to rely on space-based production of the film panels, joining them to a deploy-able tension structure. Sails in this class would offer high area per unit mass and hence accelerations up to "fifty times higher" than designs based on deploy-able plastic films.<ref name=Drexler />
The material developed for the Drexler solar sail was a thin aluminium film with a baseline thickness of 0.1&nbsp;µm, to be fabricated by vapor deposition in a space-based system. Drexler used a similar process to prepare films on the ground. As anticipated, these films demonstrated adequate strength and robustness for handling in the laboratory and for use in space, but not for folding, launch, and deployment.

Research by Geoffrey Landis in 1998–1999, funded by the [[Organization:NASA Institute for Advanced Concepts|NASA Institute for Advanced Concepts]], showed that various materials such as alumina for laser lightsails and carbon fiber for microwave pushed lightsails were superior sail materials to the previously standard aluminium or Kapton films.<ref>{{cite web|url=http://www.niac.usra.edu/files/studies/final_report/4Landis.pdf|title=Advanced Solar- and Laser-pushed Lightsail Concepts|author=Geoffrey A. Landis, Ohio Aerospace Institute|year=1999}}</ref>

In 2000, Energy Science Laboratories developed a new carbon fiber material that might be useful for solar sails.<ref name="carbonsail_000302.html">{{cite web |url=http://www.space.com/businesstechnology/technology/carbonsail_000302.html |work=SPACE.com |title=Breakthrough In Solar Sail Technology |archive-url=https://web.archive.org/web/20110101191444/http://www.space.com/businesstechnology/technology/carbonsail_000302.html |archive-date=January 1, 2011 |url-status=dead <!--alive, but it's now a different text-->}}</ref><ref>{{cite web|url=http://sbir.nasa.gov/SBIR/abstracts/99/sbir/phase1/SBIR-99-1-25.02-2034.html|title=Carbon Solar Sail|website=sbir.nasa.gov|access-date=2015-12-25|archive-date=2011-10-22|archive-url=https://web.archive.org/web/20111022203607/http://sbir.nasa.gov/SBIR/abstracts/99/sbir/phase1/SBIR-99-1-25.02-2034.html|url-status=dead}}</ref> The material is over 200 times thicker than conventional solar sail designs, but it is so porous that it has the same mass. The rigidity and durability of this material could make solar sails that are significantly sturdier than plastic films. The material could self-deploy and should withstand higher temperatures.

There has been some theoretical speculation about using molecular manufacturing techniques to create advanced, strong, hyper-light sail material, based on [[Physics:Carbon nanotube|nanotube]] mesh weaves, where the weave "spaces" are less than half the wavelength of light impinging on the sail. While such materials have so far only been produced in laboratory conditions, and the means for manufacturing such material on an industrial scale are not yet available, such materials could mass less than 0.1&nbsp;g/m<sup>2</sup>,<ref>{{cite web|url=http://www.physorg.com/news5890.html |title=Researchers produce strong, transparent carbon nanotube sheets |publisher=Physorg.com |date=2005-08-18 |access-date=2011-01-18}}</ref> making them lighter than any current sail material by a factor of at least 30. For comparison, 5 micrometre thick Mylar sail material mass 7&nbsp;g/m<sup>2</sup>, aluminized Kapton films have a mass as much as 12&nbsp;g/m<sup>2</sup>,<ref name=jpl /> and Energy Science Laboratories' new carbon fiber material masses 3&nbsp;g/m<sup>2</sup>.<ref name="carbonsail_000302.html"/>

The least dense metal is [[Chemistry:Lithium|lithium]], about 5 times less dense than aluminium.  Fresh, unoxidized surfaces are reflective.  At a thickness of 20&nbsp;nm, lithium has an area density of 0.011&nbsp;g/m<sup>2</sup>.  A high-performance sail could be made of lithium alone at 20&nbsp;nm (no emission layer).  It would have to be fabricated in space and not used to approach the Sun. In the limit, a sail craft might be constructed with a total areal density of around 0.02&nbsp;g/m<sup>2</sup>, giving it a lightness number of 67 and a<sub>c</sub> of about 400&nbsp;mm/s<sup>2</sup>. [[Chemistry:Magnesium|Magnesium]] and [[Chemistry:Beryllium|beryllium]] are also potential materials for high-performance sails.  These 3 metals can be alloyed with each other and with aluminium.<ref name="Wright" />

===Reflection and emissivity layers===
Aluminium is the common choice for the reflection layer.  It typically has a thickness of at least 20&nbsp;nm, with a reflectivity of 0.88 to 0.90.  Chromium is a good choice for the emission layer on the face away from the Sun.  It can readily provide emissivity values of 0.63 to 0.73 for thicknesses from 5 to 20&nbsp;nm on plastic film.  Usable emissivity values are empirical because thin-film effects dominate; bulk emissivity values do not hold up in these cases because material thickness is much thinner than the emitted wavelengths.<ref name="Wright Ch4">Wright, ibid. Ch 4</ref>

===Fabrication===
Sails are fabricated on Earth on long tables where ribbons are unrolled and joined to create the sails. Sail material needed to have as little weight as possible because it would require the use of the shuttle to carry the craft into orbit. Thus, these sails are packed, launched, and unfurled in space.<ref>Rowe, W. m. 'Sail film materials and supporting structure for a solar sail, a preliminary design, volume 4." Jet Propulsion Lab. California, Pasadena, California.</ref>

In the future, fabrication could take place in orbit inside large frames that support the sail.  This would result in lower mass sails and elimination of the risk of deployment failure.

==Operations==
[[File:Sail-InOut.gif|thumb|A solar sail can spiral inward or outward by setting the sail angle]]

===Changing orbits===
Sailing operations are simplest in interplanetary orbits, where altitude changes are done at low rates. For outward bound trajectories, the sail force vector is oriented forward of the Sun line, which increases orbital energy and angular momentum, resulting in the craft moving farther from the Sun. For inward trajectories, the sail force vector is oriented behind the Sun line, which decreases orbital energy and angular momentum, resulting in the craft moving in toward the Sun.  It is worth noting that only the Sun's gravity pulls the craft toward the Sun—there is no analog to a sailboat's tacking to windward. To change orbital inclination, the force vector is turned out of the plane of the velocity vector.

In orbits around planets or other bodies, the sail is oriented so that its force vector has a component along the velocity vector, either in the direction of motion for an outward spiral, or against the direction of motion for an inward spiral.

Trajectory optimizations can often require intervals of reduced or zero thrust.  This can be achieved by rolling the craft around the Sun line with the sail set at an appropriate angle to reduce or remove the thrust.<ref name="Wright" />

===Swing-by maneuvers===
A close solar passage can be used to increase a craft's energy.  The increased radiation pressure combines with the efficacy of being deep in the Sun's gravity well to substantially increase the energy for runs to the outer Solar System.  The optimal approach to the Sun is done by increasing the orbital eccentricity while keeping the energy level as high as practical.  The minimum approach distance is a function of sail angle, thermal properties of the sail and other structure, load effects on structure, and sail optical characteristics (reflectivity and emissivity).  A close passage can result in substantial optical degradation.  Required turn rates can increase substantially for a close passage.  A sail craft arriving at a star can use a close passage to reduce energy, which also applies to a sail craft on a return trip from the outer Solar System.

A lunar swing-by can have important benefits for trajectories leaving from or arriving at Earth.  This can reduce trip times, especially in cases where the sail is heavily loaded.  A swing-by can also be used to obtain favorable departure or arrival directions relative to Earth.

A planetary swing-by could also be employed similar to what is done with coasting spacecraft, but good alignments might not exist due to the requirements for overall optimization of the trajectory.<ref>Wright, ibid., Ch 6 and Appendix C.</ref>

The following table lists some example concepts using beamed laser propulsion as proposed by the physicist [[Biography:Robert L. Forward|Robert L. Forward]]:<ref>{{cite book | author= Landis, Geoffrey A. | chapter= The Ultimate Exploration: A Review of Propulsion Concepts for Interstellar Flight | title= Interstellar Travel and Multi-Generation Space Ships | editor= Yoji Kondo | editor2= Frederick Bruhweiler | editor3= John H. Moore, Charles Sheffield |page=52 | publisher= Apogee Books | date= 2003 | isbn= 978-1-896522-99-9}}</ref>

{| class="wikitable"
|-
! Mission !! Laser Power !! Vehicle Mass !! Acceleration !! Sail Diameter !! Maximum Velocity (% of the speed of light)
|-
| colspan=6| 1. Flyby – Alpha Centauri, 40 years
|-
| ''outbound stage'' || 65 GW || 1 t || 0.036 g || 3.6&nbsp;km || 11% @ 0.17 ly
|-
| colspan=6| 2. Rendezvous – Alpha Centauri, 41 years
|-
| ''outbound stage'' || 7,200 GW|| 785 t || 0.005 g || 100&nbsp;km || 21% @ 4.29 ly
|-
| ''deceleration stage'' || 26,000 GW || 71 t || 0.2 g || 30&nbsp;km || 21% @ 4.29 ly
|-
| colspan=6| 3. Crewed – Epsilon Eridani, 51 years (including 5 years exploring star system)
|-
| ''outbound stage'' || 75,000,000 GW || 78,500 t || 0.3 g || 1000&nbsp;km || 50% @ 0.4 ly
|-
| ''deceleration stage'' || 21,500,000 GW || 7,850 t || 0.3 g || 320&nbsp;km || 50% @ 10.4 ly
|-
| ''return stage'' || 710,000 GW || 785 t || 0.3 g || 100&nbsp;km || 50% @ 10.4 ly
|-
| ''deceleration stage'' || 60,000 GW || 785 t || 0.3 g || 100&nbsp;km || 50% @ 0.4 ly
|}

====Interstellar travel catalog to use photogravitational assists for a full stop====

{| class="wikitable"
|-
! Name !! Travel time<br /> (yr)!!  Distance<br />  (ly)!! Luminosity<br /> ([[Astronomy:Sun|L<sub>☉</sub>]])
|-
| ''Sirius A'' || 68.90 || 8.58 || 24.20
|-
| ''α Centauri A'' || 101.25 || 4.36 || 1.52
|-
| ''α Centauri B'' || 147.58|| 4.36 ||  0.50
|-
| ''Procyon A'' || 154.06 || 11.44 || 6.94
|-
| ''Vega'' || 167.39 ||25.02 || 50.05
|-
| '' Altair'' || 176.67 ||  16.69 ||  10.70
|-
| ''Fomalhaut A'' || 221.33 || 25.13 || 16.67
|-
| ''Denebola'' || 325.56 ||  35.78||  14.66
|-
| ''Castor A'' || 341.35|| 50.98 || 49.85
|-
| ''Epsilon Eridani'' ||  363.35 || 10.50 || 0.50
|}
* Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
* Lightsail has a nominal mass-to-surface ratio (σ<sub>nom</sub>) of 8.6×10<sup>−4</sup> gram m<sup>−2</sup> for a nominal graphene-class sail.
* Area of the Lightsail, about 10<sup>5</sup> m<sup>2</sup> = (316 m)<sup>2</sup>
* Velocity up to 37,300&nbsp;km s<sup>−1</sup> (12.5% c)
.
Ref:<ref>{{cite journal |arxiv=1704.03871 |title=Optimized trajectories to the nearest stars using lightweight high-velocity photon sails |first1=René|last1=Heller |first2=Michael|last2=Hippke |first3=Pierre|last3=Kervella |journal=The Astronomical Journal |date=2017|volume=154 |issue=3 |page=115 |doi=10.3847/1538-3881/aa813f |bibcode=2017AJ....154..115H |s2cid=119070263 |doi-access=free }}</ref>

==Projects operating or completed==

===Attitude (orientation) control===
Both the [[Astronomy:Mariner 10|Mariner 10]] mission, which flew by the planets [[Astronomy:Mercury (planet)|Mercury]] and [[Astronomy:Venus|Venus]], and the [[Astronomy:MESSENGER|MESSENGER]] mission to Mercury demonstrated the use of solar pressure as a method of [[Astronomy:Spacecraft attitude control|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 [[Engineering:Reaction wheel|reaction wheel]]s and chemical thruster.

MTSAT-1R ([[Engineering:Multi-Functional Transport Satellite|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.

===Ground deployment tests===
NASA has successfully tested deployment technologies on small scale sails in vacuum chambers.<ref>{{Cite web|url=https://www.nasa.gov/vision/universe/roboticexplorers/solar_sails.html|title=NASA - Solar Sails Could Send Spacecraft 'Sailing' Through Space|website=www.nasa.gov|access-date=2019-07-22|archive-date=2016-11-15|archive-url=https://web.archive.org/web/20161115114138/http://www.nasa.gov/vision/universe/roboticexplorers/solar_sails.html|url-status=dead}}</ref>

In 1999, a full-scale deployment of a solar sail was tested on the ground at DLR/ESA in Cologne.<ref>{{cite web|url=http://www.esa.int/esapub/bulletin/bullet98/LEIPOLD.pdf|title=Full-scale deployment test of the DLR/ESA Solar Sail|year=1999}}</ref>

===Suborbital tests ===

[[Engineering:Cosmos 1|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 [[Engineering:M-V|M-V]] rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely.<ref>{{cite web|url=http://space.skyrocket.de/doc_sdat/ssp.htm |title=SSSat 1, 2 |publisher=Space.skyrocket.de |access-date=2011-01-18}}</ref>

On August 9, 2004, the Japanese [[Organization:Institute of Space and Astronautical Science|ISAS]] successfully deployed two prototype solar sails from a sounding rocket. A clover-shaped sail was deployed at 122&nbsp;km altitude and a fan-shaped sail was deployed at 169&nbsp;km altitude. Both sails used 7.5-[[Micrometre|micrometer]] film. The experiment purely tested the deployment mechanisms, not propulsion.<ref>{{cite web|url=http://www.planetary.org/news/2004/0810_Japanese_Researchers_Successfully_Test.html |archive-url=https://web.archive.org/web/20060203030741/http://www.planetary.org/news/2004/0810_Japanese_Researchers_Successfully_Test.html |url-status=dead |archive-date=2006-02-03 |title=Cosmos 1 - Solar Sail (2004) Japanese Researchers Successfully Test Unfurling of Solar Sail on Rocket Flight |year=2004 }}</ref>

===Znamya 2===
On February 4, 1993, the Znamya 2, a 20-meter wide aluminized-mylar reflector, was successfully deployed from the Russian [[Astronomy:Mir|Mir]] space station. It was the first thin film reflector of such type successfully deployed in space using the mechanism based on centrifugal force.<ref name="«folger»">Tim Folger, «New moon — Russian satellite acts as a mirror to light remote areas» ''Discover'', Jan, 1994 ([http://findarticles.com/p/articles/mi_m1511/is_n1_v15/ai_14898893 web version] {{webarchive|url=https://web.archive.org/web/20080920035018/http://findarticles.com/p/articles/mi_m1511/is_n1_v15/ai_14898893}}, (accessed 2008 August 29)).</ref> Although the deployment succeeded, propulsion was not demonstrated. A second test in 1999, Znamya 2.5, failed to deploy properly.
[[File:Znamya-2.jpg|thumb|Znamya-2 (Знамя-2) after its deployment]]

===IKAROS 2010===
{{Main|Engineering:IKAROS}}
[[File:IKAROS IAC 2010.jpg|thumb|220px|The model of IKAROS at the 61st [[Organization:International Astronautical Congress|International Astronautical Congress]] in 2010]]

On 21 May 2010, Japan Aerospace Exploration Agency (JAXA) launched the [[Philosophy:World|world]]'s first [[Astronomy:Interplanetary spaceflight|interplanetary]] solar sail [[Engineering:Spacecraft|spacecraft]] "[[Engineering:IKAROS|IKAROS]]" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) to Venus.<ref>{{cite web|url=http://www.jspec.jaxa.jp/e/activity/ikaros.html |archive-url=https://web.archive.org/web/20080922170700/http://www.jspec.jaxa.jp/e/activity/ikaros.html |url-status=dead |archive-date=2008-09-22 |title=IKAROS Project｜JAXA Space Exploration Center |publisher=Jspec.jaxa.jp |date=2010-05-21 |access-date=2011-01-18 }}</ref> Using a new solar-photon propulsion method,<ref>{{cite book|url=https://books.google.com/books?id=c4vJpFCs1kQC&pg=PA308|title=Protection of Materials and Structures From the Space Environment|first1=Jacob|last1=Kleiman|first2=Masahito|last2=Tagawa|first3=Yugo|last3=Kimoto|date=22 September 2012|publisher=Springer Science & Business Media|via=Google Books|isbn=9783642302299}}</ref> it was the first true solar sail spacecraft fully propelled by sunlight,<ref>[https://www.newscientist.com/article/mg20627603-800-maiden-voyage-for-first-true-space-sail/ Maiden voyage for first true space sail], ''New Scientist''</ref><ref>{{cite book|url=https://books.google.com/books?id=jaExBQAAQBAJ&pg=PA169|title=Solar Sails: A Novel Approach to Interplanetary Travel|first1=Giovanni|last1=Vulpetti|first2=Les|last2=Johnson|first3=Gregory L.|last3=Matloff|date=5 November 2014|publisher=Springer|via=Google Books|isbn=9781493909414}}</ref> and was the first spacecraft to succeed in solar sail flight.<ref>{{cite book|url=https://books.google.com/books?id=9tP-CgAAQBAJ&pg=PA32|title=Human Spaceflight: From Mars to the Stars|first=Louis|last=Friedman|date=5 November 2015|publisher=University of Arizona Press|via=Google Books|isbn=9780816531462}}</ref>

JAXA successfully tested IKAROS in 2010. The goal was to deploy and control the sail and, for the first time, to determine the minute orbit perturbations caused by light pressure. Orbit determination was done by the nearby [[Engineering:Akatsuki (spacecraft)|AKATSUKI probe]] from which IKAROS detached after both had been brought into a transfer orbit to Venus. The total effect over the six month flight was 100&nbsp;m/s.<ref>{{cite web|url=http://www.isas.jaxa.jp/e/forefront/2011/tsuda/index.shtml|title=Solar Sail Navigation Technology of IKAROS|last=Tsuda|first=Yuichi|year=2011|publisher=[[Organization:JAXA|JAXA]]}}</ref>

Until 2010, no solar sails had been successfully used in space as primary propulsion systems. On 21 May 2010, the Japan Aerospace Exploration Agency (JAXA) launched the IKAROS spacecraft, which deployed a 200 m<sup>2</sup> polyimide experimental solar sail on June 10.<ref name="jaxa.jp/press/2010/06/20100611_ikaros_e">{{cite web| title = Small Solar Power Sail Demonstrator 'IKAROS' Successful Solar Sail Deployment | work = JAXA website press release | publisher = Japan Aerospace Exploration Agency | date = 2010-06-11 | url = http://www.jaxa.jp/press/2010/06/20100611_ikaros_e.html | access-date = 2010-06-17}}</ref><ref name=Nature>{{Cite news| title=News briefing: 27 May 2010 | url=http://www.nature.com/news/2010/100526/full/465402a.html | work= NatureNEWS | date=26 May 2010 | access-date= 2 June 2010}}</ref><ref>{{cite web | author=Samantha Harvey | title=Solar System Exploration: Missions: By Target: Venus: Future: Akatsuki | url=http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Akatsuki | publisher=NASA | date=21 May 2010 | access-date=2010-05-21 | archive-date=2010-05-27 | archive-url=https://web.archive.org/web/20100527210311/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Akatsuki | url-status=dead }}</ref> In July, the next phase for the demonstration of acceleration by radiation began. On 9 July 2010, it was verified that IKAROS collected radiation from the Sun and began photon acceleration by the orbit determination of IKAROS by range-and-range-rate (RARR) that is newly calculated in addition to the data of the relativization accelerating speed of IKAROS between IKAROS and the Earth that has been taken since before the Doppler effect was utilized.<ref name="http://www.jaxa.jp/press/2010/07/20100709_ikaros_j.html">{{cite web| title = About the confirmation of photon acceleration of "IKAROS" the small solar-sail demonstrating craft ('''There is not English press release yet''')| work = JAXA website press release | publisher = Japan Aerospace Exploration Agency | date = 2010-07-09 | url = http://www.jaxa.jp/press/2010/07/20100709_ikaros_j.html| access-date = 2010-07-10 }}</ref> The data showed that IKAROS appears to have been solar-sailing since 3 June when it deployed the sail.

IKAROS has a diagonal spinning square sail 14×14 m (196 m<sup>2</sup>) made of a {{convert|adj=on|7.5|μm|mm}} thick sheet of [[Chemistry:Polyimide|polyimide]]. The polyimide sheet had a mass of about 10 grams per square metre.<!-- calculated from polyimide density 1430 kg/m^3 --> A thin-film solar array is embedded in the sail. Eight LCD panels are embedded in the sail, whose reflectance can be adjusted for [[Astronomy:Spacecraft attitude control|attitude control]].<ref name=jaxa20100311>{{cite web | title=Small Solar Power Sail Demonstrator | url=http://www.jaxa.jp/projects/sat/ikaros/index_e.html | publisher=JAXA | date=11 March 2010 | access-date=2010-05-07 | archive-date=2013-10-30 | archive-url=https://web.archive.org/web/20131030175323/http://www.jaxa.jp/projects/sat/ikaros/index_e.html | url-status=dead }}</ref><ref>{{cite web|url=http://www.jspec.jaxa.jp/e/activity/ikaros.html |archive-url=https://web.archive.org/web/20080922170700/http://www.jspec.jaxa.jp/e/activity/ikaros.html |url-status=dead |archive-date=22 September 2008 |title=IKAROS Project |year=2008 |publisher=JAXA |access-date=30 March 2010 }}</ref> IKAROS spent six months traveling to Venus, and then began a three-year journey to the far side of the Sun.<ref>{{cite magazine| last = McCurry | first = Justin | title = Space yacht Ikaros ready to cast off for far side of the Sun | magazine = The Guardian Weekly | date = 2010-05-17 | url = https://www.theguardian.com/world/2010/may/17/space-yacht-ikaros-japan-venus | access-date = 2010-05-18 | location=London}}</ref>

===NanoSail-D 2010===
[[File:Nano Sail D.jpg|right|thumb|A photo of the experimental solar sail, NanoSail-D.]]

A team from the NASA [[Organization:Marshall Space Flight Center|Marshall Space Flight Center]] (Marshall), along with a team from the NASA [[Organization:Ames Research Center|Ames Research Center]], developed a solar sail mission called NanoSail-D, which was lost in a launch failure aboard a [[Engineering:Falcon 1|Falcon 1]] rocket on 3 August 2008.<ref>{{Cite web|url=http://www.nasaspaceflight.com/content/?cid=5482|archive-url=https://web.archive.org/web/20080811134536/http://www.nasaspaceflight.com/content/?cid=5482|url-status=dead|title=NASASpaceflight.com - SpaceX Falcon I FAILS during first stage flight|archive-date=August 11, 2008}}</ref><ref>{{cite web|url=https://science.nasa.gov/headlines/y2008/26jun_nanosaild.htm?list1097511 |archive-url=https://web.archive.org/web/20090211221207/https://science.nasa.gov/headlines/y2008/26jun_nanosaild.htm?list1097511 |url-status=dead |archive-date=2009-02-11 |title=NASA to Attempt Historic Solar Sail Deployment |publisher=NASA |date=2008-06-26 }}</ref> The second backup version, NanoSail-D2, also sometimes called simply NanoSail-D,<ref>{{cite web|url=http://www.nasa.gov/connect/chat/nanosail_chat2_prt.htm|title=NASA Chat: First Solar Sail Deploys in Low-Earth Orbit|date=2011-01-27|publisher=NASA|quote=Sometimes the satellite is called NanoSail-D and sometimes NanoSail-D2. ... Dean: The project is just NanoSail-D. NanoSail-D2 is the serial #2 version.|access-date=18 May 2012|archive-date=2012-06-22|archive-url=https://web.archive.org/web/20120622134237/http://www.nasa.gov/connect/chat/nanosail_chat2_prt.htm|url-status=dead}}</ref> was launched with FASTSAT on a [[Engineering:Minotaur IV|Minotaur IV]] on November 19, 2010, becoming NASA's first solar sail deployed in low earth orbit. The objectives of the mission were to test sail deployment technologies, and to gather data about the use of solar sails as a simple, "passive" means of de-orbiting dead satellites and space debris.<ref>{{cite web|url=http://www.nasa.gov/centers/marshall/news/news/releases/2011/11-055.html|title=NASA - NASA's NanoSail-D Satellite Continues to Slowly De-Orbit Earth's Upper Atmosphere|website=www.nasa.gov|access-date=2012-01-04|archive-date=2012-01-06|archive-url=https://web.archive.org/web/20120106051247/http://www.nasa.gov/centers/marshall/news/news/releases/2011/11-055.html|url-status=dead}}</ref> The NanoSail-D structure was made of aluminium and plastic, with the spacecraft massing less than {{convert |10|lb|kg}}. The sail has about {{convert|100|sqft|m2}} of light-catching surface. After some initial problems with deployment, the solar sail was deployed and over the course of its 240-day mission reportedly produced a "wealth of data" concerning the use of solar sails as passive deorbit devices.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/smallsats/11-148.html|title=NASA - NASA's Nanosail-D 'Sails' Home -- Mission Complete|website=www.nasa.gov|access-date=2012-01-04|archive-date=2011-12-01|archive-url=https://web.archive.org/web/20111201161645/http://www.nasa.gov/mission_pages/smallsats/11-148.html|url-status=dead}}</ref> 

[[Organization:NASA|NASA]] launched the second NanoSail-D unit stowed inside the FASTSAT satellite on the Minotaur IV on November 19, 2010. The ejection date from the FASTSAT microsatellite was planned for December 6, 2010, but deployment only occurred on January 20, 2011.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/smallsats/nanosaild.html |title=NASA - NanoSail-D Home Page |publisher=Nasa.gov |date=2011-01-21 |access-date=2011-01-24 |archive-date=2008-07-07 |archive-url=https://web.archive.org/web/20080707022615/http://www.nasa.gov/mission_pages/smallsats/nanosaild.html |url-status=dead }}</ref>

===Planetary Society LightSail Projects===
{{main|Engineering:LightSail}}

On June 21, 2005, a joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science  launched a prototype sail ''Cosmos 1''  from a submarine in the Barents Sea, but the [[Engineering:Volna|Volna]] rocket failed, and the spacecraft failed to reach orbit. They intended to use the sail to gradually raise the spacecraft to a higher Earth orbit over a mission duration of one month. The launch attempt sparked public interest according to Louis Friedman.<ref>{{cite web|last=Friedman|first=Louis|title=The Rise and Fall of Cosmos 1|url=http://sail.planetary.org/story-part-2.html|work=sail.planetary.org}}</ref> Despite the failed launch attempt of Cosmos 1, [[Organization:The Planetary Society|The Planetary Society]] received applause for their efforts from the space community and sparked a rekindled interest in solar sail technology.

On Carl Sagan's 75th birthday (November 9, 2009) the Planetary Society announced plans<ref>{{cite news| url=https://www.nytimes.com/2009/11/10/science/space/10solar.html| title=Setting Sail Into Space, Propelled by Sunshine| last=Overbye| first=Dennis| work=The New York Times| date=November 9, 2009| quote=Planetary Society, ... the next three years, ... series of solar-sail spacecraft dubbed LightSails|access-date=18 May 2012}}</ref> to make three further attempts, dubbed [[Engineering:LightSail#LightSail-1|LightSail-1]], [[Engineering:LightSail#LightSail-2|-2]], and -3.<ref name="planetary">{{cite web|url=http://www.planetary.org/explore/projects/lightsail-solar-sailing/lightsail-mission-faq.html |archive-url=https://web.archive.org/web/20120430105820/http://www.planetary.org/explore/projects/lightsail-solar-sailing/lightsail-mission-faq.html |url-status=dead |archive-date=30 April 2012 |title=LightSail Mission FAQ |publisher=[[Organization:The Planetary Society|The Planetary Society]] |access-date=18 May 2012 }}</ref> The new design will use a 32 m<sup>2</sup> Mylar sail, deployed in four triangular segments like NanoSail-D.<ref name="planetary"/> The launch configuration is a 3U [[Engineering:CubeSat|CubeSat]] format, and as of 2015, it was scheduled as a secondary payload for a 2016 launch on the first [[Company:SpaceX|SpaceX]] [[Engineering:Falcon Heavy|Falcon Heavy]] launch.<ref>{{cite AV media |last1=Nye| first1=Bill |title=Kickstart LightSail |url=https://www.youtube.com/watch?v=kDBzRa9RzfM | archive-url=https://ghostarchive.org/varchive/youtube/20211117/kDBzRa9RzfM| archive-date=2021-11-17 | url-status=live|time=3:20 |access-date=15 May 2015 }}{{cbignore}}</ref>

"[[Engineering:LightSail#LightSail-1|LightSail-1]]" was launched on 20 May 2015.<ref name="NBCNEWS">{{Cite web|url=https://www.nbcnews.com/science/space/blastoff-x-37b-space-plane-lightsail-solar-sail-go-space-n361931|title=Blastoff! X-37B Space Plane and LightSail Solar Sail Go Into Orbit|website=NBC News|date=20 May 2015 }}</ref> The purpose of the test was to allow a full checkout of the satellite's systems in advance of LightSail-2.  Its deployment orbit was not high enough to escape Earth's atmospheric drag and demonstrate true solar sailing.

"[[Engineering:LightSail#LightSail-2|LightSail-2]]" was launched on 25 June 2019, and deployed into a much higher low Earth orbit. Its solar sails were deployed on 23 July 2019.<ref name="NYT-20190723">{{cite news |last=Stirone |first=Shannon |title=LightSail 2 Unfurls, Next Step Toward Space Travel by Solar Sail - The Planetary Society deployed LightSail 2, aiming to further demonstrate the potential of the technology for space propulsion. |url=https://www.nytimes.com/2019/07/23/science/lightsail-solar-sail.html |date=July 23, 2019 |work={{wipe|The New York Times}} |access-date=July 24, 2019 }}</ref> It reentered the atmosphere on 17 November 2022.

===NEA Scout===
[[File:Near Earth Asteroid Scout.jpg|thumb|NEA Scout concept: a controllable CubeSat solar sail spacecraft]]
{{main|Astronomy:Near-Earth Asteroid Scout}}

The Near-Earth Asteroid Scout (NEA Scout) was a mission jointly developed by [[Organization:NASA|NASA]]'s [[Organization:Marshall Space Flight Center|Marshall Space Flight Center]] (MSFC) and the [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]] (JPL), consisting of a controllable low-cost [[Engineering:CubeSat|CubeSat]] solar sail spacecraft capable of encountering [[Astronomy:Near-Earth asteroid|near-Earth asteroid]]s (NEA).<ref>{{cite web |date=2015-10-30 |title=NEA Scout |url=https://www.nasa.gov/content/nea-scout |access-date=February 11, 2016 |publisher=NASA |archive-date=2017-05-23 |archive-url=https://web.archive.org/web/20170523141323/https://www.nasa.gov/content/nea-scout/ |url-status=dead }}</ref> Four {{cvt|7|m}} booms were to deploy, unfurling the {{cvt|83|m2}} aluminized polyimide solar sail.<ref name="McNutt">{{cite journal |last1=McNutt |first1=Leslie |last2=Castillo-Rogez |first2=Julie |date=2014 |title=Near-Earth Asteroid Scout |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140012882.pdf |journal=NASA |publisher=American Institute of Aeronautics and Astronautics |access-date=2015-05-13}}</ref><ref name="Gunter2015">{{cite web |last=Krebs |first=Gunter Dirk |date=13 April 2015 |title=NEA-Scout |url=http://space.skyrocket.de/doc_sdat/nea-scout.htm |access-date=2015-05-13}}</ref><ref name="Castillo">{{cite web |last1=Castillo-Rogez |first1=Julie |last2=Abell |first2=Paul |title=Near Earth Asteroid Scout Mission |url=http://www.lpi.usra.edu/sbag/meetings/jul2014/presentations/0930_Thu_Castillo_NEAScout.pdf |access-date=2015-05-13 |work=NASA |publisher=Lunar and Planetary Institute}}</ref> In 2015, NASA announced it had selected NEA Scout to launch as one of several secondary payloads aboard [[Engineering:Artemis 1|Artemis 1]], the first flight of the agency's heavy-lift [[Astronomy:Space Launch System|SLS]] launch vehicle.<ref>{{cite web |last=Gebhardt |first=Chris |date=November 27, 2015 |title=NASA identifies secondary payloads for SLS's EM-1 mission |url=http://www.nasaspaceflight.com/2015/11/nasa-identifies-secondary-payloads-sls-em-1/ |publisher=NASAspaceflight}}</ref> However, the craft was considered lost with the failure to establish communications shortly after launch in 2022.<ref name="Dickinson2022">{{cite news |last=Dickinson |first=David |date=6 December 2022 |title=Status Update: Artemis 1's SmallSat Missions |newspaper=Sky & Telescope |publisher=Sky&Telescope |url=https://skyandtelescope.org/astronomy-news/status-update-artemis-1s-smallsat-missions/ |access-date=8 December 2022}}</ref>

== Projects proposed or cancelled or not selected ==
Despite the losses of ''Cosmos 1'' and NanoSail-D (which were due to failure of their launchers), scientists and engineers around the world remain encouraged and continue to work on solar sails. While most direct applications created so far intend to use the sails as inexpensive modes of cargo transport, some scientists are investigating the possibility of using solar sails as a means of transporting humans. This goal is strongly related to the management of very large (i.e. well above 1&nbsp;km<sup>2</sup>) surfaces in space and the sail making advancements. Development of solar sails for crewed space flight is still in its infancy.

===Sunjammer 2015===
{{Main|Engineering:Sunjammer (spacecraft)}}
A technology demonstration sail craft, dubbed [[Engineering:Sunjammer (spacecraft)|''Sunjammer'']], was in development with the intent to prove the viability and value of sailing technology.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/tdm/solarsail/solarsail_overview.html |title=Nasa Solar Sail Demonstration |publisher=www.nasa.gov |date=2013-10-28 |access-date=2013-03-25 |archive-date=2015-12-24 |archive-url=https://web.archive.org/web/20151224180251/http://www.nasa.gov/mission_pages/tdm/solarsail/solarsail_overview.html |url-status=dead }}</ref> ''Sunjammer'' had a square sail, {{convert|38|m}} wide on each side, giving it an effective area of {{convert|1200|m2}}.  It would have traveled from the Sun-Earth {{L1}} [[Astronomy:Lagrangian point|Lagrangian point]] {{convert|1.5|e6km|mi|abbr=off}} from Earth to a distance of {{convert|3|e6km|e6mi|abbr=off}}.<ref>{{cite web|url=http://www.space.com/19565-worlds-largest-solar-sail-sunjammer.html|title=NASA to Launch World's Largest Solar Sail in 2014|author=Leonard David|publisher=Space.com|date=January 31, 2013|access-date=June 13, 2013}}</ref> The demonstration was expected to launch on a [[Engineering:Falcon 9|Falcon 9]] in January 2015.<ref name="Yahoo">{{cite web|url=https://news.yahoo.com/worlds-largest-solar-sail-launch-november-2014-214450113.html|title=World's Largest Solar Sail to Launch in November 2014|author=Mike Wall|publisher=Space.com|date=June 13, 2013|access-date=June 13, 2013}}</ref> It would have been a secondary payload, released after the placement of the [[Engineering:Deep Space Climate Observatory|DSCOVR]] climate satellite at the L1 point.<ref name="Yahoo"/> Citing a lack of confidence in the ability of its contractor [[Company:LGarde|L'Garde]] to deliver, the mission was cancelled by NASA in October 2014.<ref>{{cite news|url=http://www.spacenews.com/article/civil-space/42227nasa-nixes-sunjammer-mission-cites-integration-schedule-risk|archive-url=https://archive.today/20141018025439/http://www.spacenews.com/article/civil-space/42227nasa-nixes-sunjammer-mission-cites-integration-schedule-risk|url-status=dead|archive-date=October 18, 2014|title=NASA Nixes Sunjammer Mission, Cites Integration, Schedule Risk|last=Leone|first=Dan|work=spacenews.com|date=October 17, 2014}}</ref>


===OKEANOS===
{{main|Astronomy:OKEANOS}}
OKEANOS (Outsized Kite-craft for Exploration and Astronautics in the Outer Solar System) was a proposed mission concept by Japan's [[Organization:JAXA|JAXA]] to Jupiter's Trojan asteroids using a hybrid solar sail for propulsion; the sail would have been covered with thin [[Physics:Solar panels on spacecraft|solar panels]] to power an ion engine. ''In-situ'' analysis of the collected samples would have been performed by either direct contact or using a lander carrying a high-resolution mass spectrometer. A lander and a sample-return to Earth were options under study.<ref name="Matsumoto 2015">[http://www.hayabusa.isas.jaxa.jp/kawalab/astro/pdf/2015A_16.pdf Sampling Scenario for the Trojan Asteroid Exploration Mission] {{Webarchive|url=https://web.archive.org/web/20171231155341/http://www.hayabusa.isas.jaxa.jp/kawalab/astro/pdf/2015A_16.pdf |date=2017-12-31 }} (PDF). Jun Matsumoto, Jun Aoki, Yuske Oki, Hajime Yano. 2015.</ref> The OKEANOS Jupiter Trojan Asteroid Explorer was a finalist for Japan's [[Organization:Institute of Space and Astronautical Science|ISAS]]{{'}} 2nd Large-class mission to be launched in the late 2020s. However, it was not selected.


===''Solar Cruiser''===
{{main|Astronomy:Solar Cruiser}}

In August 2019, NASA awarded the ''Solar Cruiser'' team $400,000 for nine-month mission concept studies. The spacecraft would have a {{cvt|1672|sqm}} solar sail and would orbit the Sun in a polar orbit, while the [[Astronomy:Coronagraph|coronagraph]] instrument would enable simultaneous measurements of the [[Astronomy:Sun#Magnetic field|Sun's magnetic field]] structure and velocity of [[Astronomy:Coronal mass ejection|coronal mass ejection]]s.<ref name='PR Helio'>[https://www.nasa.gov/press-release/nasa-selects-proposals-to-demonstrate-smallsat-technologies-to-study-interplanetary NASA Selects Proposals to Demonstrate SmallSat Technologies to Study Interplanetary Space.] NASA press release, 15 August 2019.</ref> If selected for further development, it would have launched in 2025. However, ''Solar Cruiser'' was not approved to advance to phase C of its development cycle and was subsequently discontinued.<ref>{{cite web |last=Christe |first=Steve |url=https://hesto.smce.nasa.gov/2023/08/02/solar-cruiser-enabling-new-vistas-for-heliophysics-science/ |title=Solar Cruiser: Enabling new vistas for Heliophysics Science |work=Heliophysics Strategic Technology Office |publisher=[[Organization:NASA|NASA]] |date=2 August 2023 |access-date=5 December 2023}}</ref>

==Projects still in development or unknown status==

===Gossamer deorbit sail===
{{asof|2013|12}}, the [[Organization:European Space Agency|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 {{convert|700|kg}}) artificial satellites from [[Astronomy:Low Earth orbit|low Earth orbit]]s.  The launch mass is {{convert|2|kg}} with a launch volume of only {{convert|15|*|15|*|25|cm|ft}}.  Once deployed, the sail would expand to {{convert|5|x|5|m|ft}} and would use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite [[Astronomy:Atmospheric entry|reentry]].<ref name=ps20131226>
{{cite news |last=Messier|first=Doug |title=ESA Developing Solar Sail to Safely Deorbit Satellites |url=http://www.parabolicarc.com/2013/12/26/esa-solar-sail-deorbiter/ |access-date=2013-12-28 |newspaper=Parabolic Arc |date=2013-12-26 }}</ref>


===Breakthrough Starshot===
{{main|Astronomy:Breakthrough Starshot}}
The well-funded Breakthrough Starshot project announced on April 12, 2016, aims to develop a fleet of 1000 light sail nanocraft carrying miniature cameras, propelled by ground-based lasers and send them to [[Astronomy:Alpha Centauri|Alpha Centauri]] at 20% the speed of light.<ref name="Starshot home">{{cite web |url=http://breakthroughinitiatives.org/Initiative/3 |title=Breakthrough Starshot |work=Breakthrough Initiatives |date=12 April 2016 |access-date=2016-04-12 }}</ref><ref name="concept'">[http://breakthroughinitiatives.org/Concept/3 Starshot - Concept].</ref><ref>{{cite web|url=http://breakthroughinitiatives.org/Target/3|title=Breakthrough Initiatives|website=breakthroughinitiatives.org}}</ref> The trip would take 20 years.

== In popular culture ==
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.

[[Biography:Arthur C. Clarke|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.<ref>[http://www.isfdb.org/cgi-bin/adv_search_results.cgi?USE_1=title_title&O_1=exact&TERM_1=Sunjammer&C=AND&USE_2=title_copyright&O_2=exact&TERM_2=1964&USE_3=title_title&O_3=exact&TERM_3=&USE_4=title_title&O_4=exact&TERM_4=&USE_5=title_title&O_5=exact&TERM_5=&USE_6=title_title&O_6=exact&TERM_6=&USE_7=title_title&O_7=exact&TERM_7=&USE_8=title_title&O_8=exact&TERM_8=&USE_9=title_title&O_9=exact&TERM_9=&USE_10=title_title&O_10=exact&TERM_10=&ORDERBY=title_title&ACTION=query&START=0&TYPE=Title Sunjammer], ISFDB.</ref>

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 ({{cite episode|title=Explorers|series=Star Trek: Deep Space Nine|season=3|number=22}}).<ref>{{Cite web|url=http://www.imdb.com/title/tt0708534/?ref_=ttep_ep22|title="Star Trek Deep Space Nine" Explorers (TV Episode 1995) - IMDB|website=IMDB|date=8 February 2018}}</ref>

In the 2002 ''Star Wars'' film ''Attack of the Clones'', the main villain Count Dooku was seen using a spacecraft with solar sails.<ref>{{cite book|title=Star Wars: Attack of the Clones Incredible Cross-Sections|isbn=9780789485748|author=Curtis Saxton|publisher=DK Publishing|date=2002}}</ref>

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.

==See also==
* {{annotated link|Physics:Optical lift}}
* {{annotated link|Astronomy:Poynting–Robertson effect}}
* {{annotated link|Astronomy:Technosignature}}
* {{annotated link|Yarkovsky effect}}

==References==
{{reflist}}

==Bibliography==
*G. Vulpetti, ''Fast Solar Sailing: Astrodynamics of Special Sailcraft Trajectories'', ;;Space Technology Library'' Vol. 30, Springer, August 2012, (Hardcover) https://www.springer.com/engineering/mechanical+engineering/book/978-94-007-4776-0, (Kindle-edition), ASIN: B00A9YGY4I
*G. Vulpetti, L. Johnson, G. L. Matloff, ''Solar Sails: A Novel Approach to Interplanetary Flight'', Springer, August 2008, {{ISBN|978-0-387-34404-1}}
* J. L. Wright, ''Space Sailing'', Gordon and Breach Science Publishers, London, 1992; Wright was involved with JPL's effort to use a solar sail for a rendezvous with Halley's comet.
* ''[https://web.archive.org/web/20070930204850/http://nuke.giovannivulpetti.it/SolarSailing/tabid/56/Default.aspx NASA/CR 2002-211730, Chapter IV]''— presents an optimized escape trajectory via the H-reversal sailing mode
*G. Vulpetti, The Sailcraft Splitting Concept, ''[[Organization:Journal of the British Interplanetary Society|JBIS]]'', Vol. 59, pp.&nbsp;48–53, February 2006
*G. L. Matloff, ''Deep-Space Probes: To the Outer Solar System and Beyond'', 2nd ed., Springer-Praxis, UK, 2005, {{ISBN|978-3-540-24772-2}}
*T. Taylor, D. Robinson, T. Moton, T. C. Powell, G. Matloff, and J. Hall, "Solar Sail Propulsion Systems Integration and Analysis (for Option Period)", Final Report for NASA/MSFC, Contract No. H-35191D Option Period, Teledyne Brown Engineering Inc., Huntsville, AL, May 11, 2004
*G. Vulpetti, "Sailcraft Trajectory Options for the Interstellar Probe: Mathematical Theory and Numerical Results", the Chapter IV of NASA/CR-2002-211730, ''The Interstellar Probe (ISP): Pre-Perihelion Trajectories and Application of Holography'', June 2002
*G. Vulpetti, Sailcraft-Based Mission to The Solar Gravitational Lens, STAIF-2000, Albuquerque (New Mexico, USA), 30 January – 3 February 2000
*G. Vulpetti, "General 3D H-Reversal Trajectories for High-Speed Sailcraft", ''Acta Astronautica'', Vol. 44, No. 1, pp.&nbsp;67–73, 1999
*C. R. McInnes, ''Solar Sailing: Technology, Dynamics, and Mission Applications'', Springer-Praxis Publishing Ltd, Chichester, UK, 1999, {{ISBN|978-3-540-21062-7}}
*Genta, G., and Brusa, E., "The AURORA Project: a New Sail Layout", ''Acta Astronautica'', 44, No. 2–4, pp.&nbsp;141–146 (1999)
*S. Scaglione and G. Vulpetti, "The Aurora Project: Removal of Plastic Substrate to Obtain an All-Metal Solar Sail", special issue of ''Acta Astronautica'', vol. 44, No. 2–4, pp.&nbsp;147–150, 1999

==External links==
* [https://spectrum.ieee.org/aerospace/space-flight/deflecting-asteroids "Deflecting Asteroids"] by Gregory L. Matloff, ''IEEE Spectrum,'' April 2012
* [http://www.planetary.org/explore/projects/lightsail-solar-sailing/ Planetary Society's solar sailing project]
*[https://web.archive.org/web/20140330023506/http://astroreview.com/issue/2012/article/the-solar-photon-sail-comes-of-age The Solar Photon Sail Comes of Age] by Gregory L. Matloff
* [http://www.nasa.gov/mission_pages/smallsats/nanosaild.html NASA Mission Site for NanoSail-D] {{Webarchive|url=https://web.archive.org/web/20080707022615/http://www.nasa.gov/mission_pages/smallsats/nanosaild.html |date=2008-07-07 }}
* ''NanoSail-D'' mission: Dana Coulter, [https://web.archive.org/web/20090211221207/https://science.nasa.gov/headlines/y2008/26jun_nanosaild.htm?list1097511 "NASA to Attempt Historic Solar Sail Deployment"], NASA, June 28, 2008
* [http://www-spof.gsfc.nasa.gov/stargaze/Solsail.htm Far-out Pathways to Space: Solar Sails] {{Webarchive|url=https://web.archive.org/web/20061017194705/http://www-spof.gsfc.nasa.gov/stargaze/Solsail.htm |date=2006-10-17 }} from NASA
* [http://www.solarsails.info/ Solar Sails] Comprehensive collection of solar sail information and references, maintained by Benjamin Diedrich. [http://wiki.solarsails.info/index.php?title=Tacking_Solar_Sails Good diagrams] showing how light sailors must tack.
* [http://www.u3p.net/ U3P] Multilingual site with news and flight simulators
* [http://www.isas.jaxa.jp/e/snews/2004/0809.shtml ISAS Deployed Solar Sail Film in Space]
* [http://www.solar-thruster-sailor.info/figs/fig13.html Suggestion of a solar sail with roller reefing, hybrid propulsion and a central docking and payload station.]
* [http://www.andybrain.com/extras/solar-sail.htm Interview with NASA's JPL about solar sail technology and missions]
* [https://web.archive.org/web/20070930204850/http://nuke.giovannivulpetti.it/SolarSailing/tabid/56/Default.aspx Website with technical pdf-files about solar-sailing, including NASA report and lectures at Aerospace Engineering School of Rome University]
* [https://web.archive.org/web/20060304160747/http://www.niac.usra.edu/files/studies/final_report/4Landis.pdf Advanced Solar- and Laser-pushed Lightsail Concepts]
* {{Cite journal
 |url=http://www.andrews-space.com/images/videos/PAPERS/Pub-InterstellarTransportation(200307).pdf
 |archive-url=https://web.archive.org/web/20060311195517/http://www.andrews-space.com/images/videos/PAPERS/Pub-InterstellarTransportation%28200307%29.pdf
 |url-status=dead
 |archive-date=2006-03-11
 |title=Interstellar Transportation using Today's Physics
 |author=Andrews, D. G.
 |journal=AIAA Paper 2003-4691
 |year=2003
}}
*[https://web.archive.org/web/20081226193057/http://www.aibep.org/ www.aibep.org: Official site of American Institute of Beamed Energy Propulsion]
* [http://www.spacesailing.com/ Space Sailing] Sailing ship concepts, operations, and history of concept
* [http://www.spacesailing.net/ Bernd Dachwald's Website] Broad information on sail propulsion and missions

{{spacecraft propulsion}}
{{emerging technologies|topics=yes|space=yes}}

{{DEFAULTSORT:Solar Sail}}
[[Category:Spacecraft attitude control]]
[[Category:Spacecraft propulsion]]
[[Category:Spacecraft components]]
[[Category:Interstellar travel]]
[[Category:Microwave technology]]
[[Category:Photonics]]

{{Sourceattribution|Solar sail}}