Editing Solar sail (section)

==Applications==
Potential applications for sail craft range throughout the [[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 [[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 [[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 [[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 [[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 (astronomy)|heliopause]], six and a half years to reach the Sun’s inner [[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===
[[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 "[[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 [[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 ''[[The Case for Mars]]'', [[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 [[global warming]]. On-board state-of-the-art [[accelerometer]]s would measure shifts in the pressure differential between incoming solar and outgoing [[thermal radiation]] on opposing sides of each satellite.   Measurement accuracy has been projected to be better than that achievable with compact [[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 [[MESSENGER]] probe orbiting [[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 [[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 [[beam-powered propulsion]] schemes using either lasers or [[maser]]s to push giant sails to a significant fraction of the [[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]] 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 [[Fresnel lens]] would need to be located at several dozen [[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 "[[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 [[evaporation]] could significantly increase the [[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 [[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 [[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 [[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=https://ui.adsabs.harvard.edu/abs/1979JBIS...32..419M/abstract |bibcode=1979JBIS...32..419M }}</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 [[low Earth orbit]] can use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite [[atmospheric entry|reentry]].<ref name=ps20131226/>  A de-orbit sail developed at [[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|archive-date = 2022-11-10|archive-url = https://web.archive.org/web/20221110230210/https://www.sstl.co.uk/media-hub/latest-news/2019/techdemosat-1-on-board-camera-captures-drag-sail-deployment|url-status = dead}}</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 [[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 [[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 [[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 [[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>