Solar sail

Solar sails (also called light sails or photon sails) are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds.

In 2010, IKAROS was the world's first spacecraft designed to use solar sailing propulsion to be successfully launched.[1]

Contents

History

The concept of using photon pressure for propulsion was first proposed by Russian scientist Konstantin Tsiolkovsky in 1921, and in 1924 he and Friedrich Zander wrote of "using tremendous mirrors of very thin sheets" and "using the pressure of sunlight to attain cosmic velocities".

The term "solar sailing" was coined in the late 1950s and popularized by Arthur C. Clarke's short story "Sunjammer" in May 1964.[2]

Physics

There are two sources of solar forces: radiation pressure, and solar wind. Radiation pressure is much stronger than wind pressure.

In 1924, the Russian space engineer Friedrich Zander proposed that, since light provides a small amount of thrust, this effect could be used as a form of space propulsion requiring no fuel. Einstein proposed (and experiments confirm) that photons have a momentum p=E/c;[3][4] therefore, each light photon absorbed by or reflecting from a surface exerts a small amount of radiation pressure. This results in forces of about 4.57x10−6 N/m2 for absorbing surfaces perpendicular to the radiation in Earth orbit, and a little less than twice as much if the radiation is reflected.[5] This was proven experimentally by Russian physicist Pyotr Nikolaevich Lebedev in 1900,[6] and independently by Nichols and Hull at Dartmouth in 1901 using a Nichols radiometer.[7]

Charged particles from the solar wind are able to cause geomagnetic storms which can knock out power grids on Earth, and point the tails of comets away from the Sun. The solar wind averages 6.7 billion tons per hour at 520 km/s with "slow" low energy coronal ejections reaching 400 km/s and "fast," higher energy ejections averaging 750 km/s. At the distance of the Earth, this results in average solar wind pressure of 3.4×10−9 N/m2, and is three orders of magnitude less than the photonic radiation pressure. Still the solar wind dominates many phenomena because its interaction cross section with gases and charged particles is about 109 times larger than that of the photons.[8]

Both of these forces are small and decrease with the inverse square distance from the Sun. Even large sails produce minute acceleration, but over time, sails can build up considerable speeds.[9]

Changing course trajectories can be accomplished in two ways. First, tilting the sail with respect to the light source changes the direction of acceleration because the force on a sail from reflected radiation and wind acts in a direction perpendicular to its surface. Smaller auxiliary vanes can be used to gently pull the main sail into its new position (see the vanes on the illustration labeled Cosmos 1, above).[10] Second, gravity from a nearby mass, such as a star or planet, will alter the direction of a spaceship.

Fly modes

Escaping planetary orbit

Sails orbit, and therefore do not need to hover or move directly toward or away from the Sun. Almost all missions would use the sail to change orbit, rather than thrusting directly away from a planet or the Sun. The sail is rotated slowly as the sail orbits around a planet so the thrust is in the direction of the orbital movement to move to a higher orbit or against it to move to a lower orbit. When an orbit is far enough away from a planet, the sail then begins similar maneuvers in orbit around the Sun.[11]

Beam propelled

Most theoretical studies of interstellar missions with a solar sail plan to push the sail with a very large laser beam-powered propulsion direct impulse beam. The thrust vector (spatial vector) would therefore be away from the Sun and toward the target.

In theory a lightsail driven by a laser or other beam from Earth can be used to slow down a spacecraft approaching a distant star or planet, by detaching part of the sail and using it to focus the beam on the forward-facing surface of the rest of the sail.[12] In practice, however, most of the slowing would happen while the two parts are at a great distance from each other, and that means that, to do that focusing, it would be necessary to give the detached part an accurate optical shape and orientation. This solution is also limited because the lasers used to accelerate or decelerate a sail ship could take years, decades, or centuries to reach the craft, depending on the distance.

Limitations of solar sails

Solar sails do not work well, if at all, in low Earth orbit below about 800 km altitude due to erosion or air drag.[13] Above that altitude they give very small accelerations that take months to build up to useful speeds. Solar sails have to be physically large, and payload size is often small. Deploying solar sails is also highly challenging to date.

Investigated sail designs

"Parachutes" would have very low mass, but theoretical studies show that they will collapse from the forces placed by shrouds. Radiation pressure does not behave like aerodynamic pressure.[14]

The highest thrust-to-mass designs known (as of 2007) were theoretical designs developed by Eric Drexler.[15] He designed a sail using reflective panels of thin aluminium film (30 to 100 nanometres thick) supported by a purely tensile structure. It rotated and would have to be continually under slight thrust. He made and handled samples of the film in the laboratory, but the material is too delicate to survive folding, launch, and deployment, hence the design relied on space-based production of the film panels, joining them to a deployable tension structure. Sails in this class would offer area per unit mass and hence accelerations up to "fifty times higher" than designs based on deployable plastic films.[15]

The highest-thrust to mass designs for ground-assembled deployable structures are square sails with the masts and 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 quite close to the Sun, where the maximum thrust is present. Control would probably use small sails on the ends of the spars.[16]

In the 1970s JPL did extensive studies of rotating blade and rotating ring sails for a mission to rendezvous with Halley's Comet. The intention was that such structures would be stiffened by their 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. So the difference in the thrust-to-mass ratio was almost nil, and the static designs were much easier to control.[16]

JPL's reference design was called the "heliogyro" and 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 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.[16]

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 manned structures. The inner ring, in particular, might be made to have artificial gravity roughly equal to the gravity on the surface of Mars.[16]

A solar sail can serve a dual function as a high-gain antenna.[17] Designs differ, but most modify the metallization pattern to create a holographic monochromatic lens or mirror in the radio frequencies of interest, including visible light.[17]

Pekka Janhunen from FMI has invented a type of solar sail called the electric solar wind sail.[18] Mechanically it has little in common with the traditional solar sail design, because the sails are replaced with straightened conducting tethers (wires) which are placed radially around the host ship. The wires are electrically charged and thus an electric field is created around the wires. The electric field of the wires extends a few tens of metres into the surrounding solar wind plasma. Because the solar wind electrons react on the electric field (similarly to the photons on a traditional solar sail), the functional radius of the wires is based on the electric field that is generated around the wire rather than the actual wire itself. This fact also makes it possible to maneuver a ship with an electric solar wind sail by regulating the electric charge of the wires. A full-sized operational electric solar wind sail would have 50-100 straightened wires with a length of about 20 km each.

A quite similar concept is the magnetic sail, which would also employ the solar wind, but interact with the magnetic charge of the particles in the wind, rather than the electric. Typically it is also constructed with wires as "sails", but in contrast to a electric sail, it uses wire loops, and runs a static current through them instead of applying a static voltage.[19]

All these designs maneuver, though the mechanisms are different. Magnetic sails bend the path of the charged protons that are in the solar wind. By changing the sails' attitudes, and the size of the magnetic fields, they can change the amount and direction of the thrust. Electric solar wind sails can perform similar maneuvers by adjusting their electrostatic fields and sail attitudes.

Sail testing in space

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” (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) spacecraft, which deployed a 200 m2 polyimide experimental solar sail on June 10.[20][21][22] In July, the next phase for the demonstration of acceleration by radiation began. On 9 July, 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.[23] 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 20 m (66 ft) made of a 7.5-micrometre (0.0075 mm) thick sheet of polyimide. A thin-film solar array is embedded in the sail. Eight LCD panels are embedded in the sail, whose reflectance can be adjusted for attitude control.[24][25] IKAROS will spend six months traveling to Venus, and then will begin a three-year journey to the far side of the Sun.[26]

Solar pressure demonstrated for attitude control

Both the Mariner 10 mission, which flew by the planets Mercury and Venus, and the MESSENGER mission to Mercury demonstrated the use of solar pressure as a method of attitude control in order to conserve attitude-control propellant.

Hayabusa also used solar pressure as a method of attitude control to compensate for broken reaction wheels and chemical thruster.

Solar sail deployment tests

NASA has successfully tested deployment technologies on small scale sails in vacuum chambers.[27]

On February 4, 1993, Znamya 2, a 20-meter wide aluminized-mylar reflector, was successfully tested from the Russian Mir space station. Although the deployment test was successful, the experiment only demonstrated the deployment, not propulsion. A second test, Znamaya 2.5, failed to deploy properly.

In 1999, a full-scale deployment test of a solar sail has been performed on ground at DLR/ESA in Cologne.[28]

On August 9, 2004, the Japanese ISAS successfully deployed two prototype solar sails from a sounding rocket. A clover type sail was deployed at 122 km altitude and a fan type sail was deployed at 169 km altitude. Both sails used 7.5 micrometer thick film. The experiment was purely a test of the deployment mechanisms, not of propulsion.[29]

Partially successful solar sail propulsion tests

A joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science launched Cosmos 1 on June 21, 2005, from a submarine in the Barents Sea, but the Volna rocket failed, and the spacecraft failed to reach orbit. A solar sail would have been used to gradually raise the spacecraft to a higher Earth orbit. The mission would have lasted for one month. A suborbital prototype test by the group failed in 2001 as well, also because of rocket failure. The same group announced plans on Carl Sagan's 75th birthday (November 9, 2009) to make three further attempts, dubbed LightSail-1, -2, and -3. The new design will use a 32-square-meter Mylar sail, deployed in four triangular segments like NanoSail-D. The launch configuration is that of three adjacent CubeSats, and is scheduled to launch on a Minotaur IV rocket in Q4 2010.[30]

A 15-meter-diameter solar sail (SSP, solar sail sub payload, soraseiru sabupeiro-do) was launched together with ASTRO-F on a M-V rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely.[31]

NanoSail-D

A team from the NASA Marshall Space Flight Center (Marshall), along with a team from the NASA Ames Research Center, developed a solar sail mission called NanoSail-D which was lost in a launch failure aboard a Falcon 1 rocket on 3 August 2008.[32][33] The second backup version, NanoSail-D2 was launched with FASTSAT on a 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 [34]. The NanoSail-D structure was made of aluminium and plastic, with the spacecraft massing less than 10 pounds (4.5 kg). The sail has about 100 square feet (9.3 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 [35].

Future solar sail propulsion tests

A team from the Surrey Space Centre at the University of Surrey are developing a solar sail demonstration mission called the "CubeSail". This mission is due to launch in late 2011. The CubeSail is based on the CubeSat standard and when stowed it will occupy a 3U standard volume (3, 100mm x 100mm x 100mm). When in orbit, it will extend four 3.6m booms, deploying a sail of 25m2. The mission's primary objective is to demonstrate deployment of a solar sail and the concept of solar sailing. Finally and at its end-of-life it will use its sail to change its ballistic coefficient and reenter the Earth's atmosphere. This final phase of the mission has attracted much media attention as it has the potential to be used on board larger spacecraft as a de-orbiting device and potentially to solve the Space debris problem.[36][37][38][39]

Sail materials

The material developed for the Drexler solar sail was a thin aluminum film with a baseline thickness of 0.1 micrometres, 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.

The most common material in current designs is aluminized 2 µm Kapton film. It resists the heat of a pass close to the Sun and still remains reasonably strong. The aluminium reflecting film is on the Sun side. The sails of Cosmos 1 were made of aluminized PET film (Mylar).

Research by Dr. Geoffrey Landis in 1998-9, funded by the 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.[40]

In 2000, Energy Science Laboratories developed a new carbon fiber material which might be useful for solar sails.[41] 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 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 g/m²,[42] 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 g/m², aluminized Kapton films have a mass as much as 12 g/m²,[16] and Energy Science Laboratories' new carbon fiber material masses 3 g/m².[41]

Applications

Satellites

Robert L. Forward pointed out that a solar sail could be used to modify the orbit of a satellite around 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 about the Sun that 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 potential of the Sun. Such an orbit could be useful for studying the properties of the Sun over long durations.

Such a spacecraft could conceivably be placed directly over a pole of the Sun, and remain at that station for lengthy durations. Likewise a solar sail-equipped spacecraft could also remain on station nearly above the polar terminator of a planet such as the Earth by tilting the sail at the appropriate angle needed to just counteract the planet's gravity.

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 focussed on one of the Martian polar ice caps to significantly warm the planet's atmosphere. Such a statite could be made from asteroid material.

Trajectory corrections

The MESSENGER probe en route to Mercury is using light pressure reacting against its solar panels to perform fine trajectory corrections.[43] By changing the angle of the solar panels relative to the Sun, the amount of solar radiation pressure can be varied to adjust the spacecraft trajectory more delicately than is possible with thrusters. Minor errors are greatly amplified by gravity assist maneuvers, so very small corrections before lead to large savings in propellant afterward.

Interstellar flight

In the 1980s, Robert Forward proposed two beam-powered propulsion schemes using either lasers or masers to push giant sails to a significant fraction of the speed of light.

In The Flight of the Dragonfly, Forward described a light sail propelled by superlasers. 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. Second, they would demand more energy than the Earth currently consumes. Third, Forward's own solution to the electrical problem requires enormous solar panel arrays to be built at or near the planet Mercury. Fourth, a planet-sized mirror or fresnel lens would be needed several dozen astronomical units from the Sun to keep the lasers focused on the sail. Fifth, 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, since the manipulation of microwave radiation is somewhat easier than the manipulation of visible light. The hypothetical "Starwisp" interstellar probe design would use a maser to drive it. Masers spread out more rapidly than optical lasers owing to their longer wavelength, and so would not have as long 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.[44] 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, designs have considered the use of a large zone plate. This would be placed at a location between the laser or maser and the spacecraft. The plate could then be propelled outward using the same energy source, thus maintaining its position so as to focus the energy on the solar sail.

Additionally, it has been theorized by da Vinci Project contributor T. Pesando that solar sail-utilizing spacecraft successful in interstellar travel could be used to carry their own zone plates or perhaps even masers to be deployed during flybys at nearby stars. Such an endeavor could allow future solar-sailed craft to effectively utilize focused energy from other stars rather than from the Earth or Sun, thus propelling them more swiftly through space and perhaps even to more distant stars. However, the potential of such a theory remains uncertain if not dubious due to the high-speed precision involved and possible payloads required.

Another more physically realistic approach would be to use the light from the home star to accelerate. The ship would first orbit continuously away around the home star until the appropriate starting velocity is reached, then the ship would begin its trip away from the system using the light from the star to keep accelerating. Beyond some distance, the ship would no longer receive enough light to accelerate it significantly, but would maintain its course due to inertia. When nearing the target star, the ship could turn its sails toward it and begin to orbit inward to decelerate. Additional forward and reverse thrust could be achieved with more conventional means of propulsion such as rockets.

Future approaches

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 km²) surfaces in space and the sail making advancements. Thus, in the near/medium term, solar sail propulsion is aimed chiefly at accomplishing a very high number of non-crewed missions in any part of the solar system and beyond.

Solar sail launching projects in 2010 and 2011

On 21 May 2010, Japan Aerospace Exploration Agency (Jaxa) launched the world's first interplanetary solar sail spacecraft "IKAROS" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) to Venus.[45] 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.[46] The Planetary Society of the United States plans to launch an artificial satellite "LightSail-1" onto the Earth's orbit in 2011.[47]

Mathematical survey

Solar Sail vessels are classified by their lightness number which is the ratio of the acceleration due to the light force on the sail to the force of gravity. (Note these both vary with the inverse square of distance. So the ratio is constant for any vehicle.) A typical reflective surface needs to provide about 4 square meters of reflective area for every 5 grams of vehicle weight to have a lightness factor of 1.[48]

The light force can be separated into the normal force (away from the light source) and the tangential force as a function of the angle A of the sail face to the light. The Normal Force per area = 8/9 cos^2 A + 1/9 cos A. The Tangential Force per area = 4/9 sin 2A.

The Extended Heliocentric Reference Frame

  1. α = 0 , δ = 0 ⇔ [λr , 0 , 0] ⇔ λ=|L|=λr
  2. α ≠ 0 , δ = 0 ⇔ [λr , λt , 0]
  3. α = 0 , δ ≠ 0 ⇔ [λr , 0 , λn].

A flight example

Conventional strategy

Optimal strategy

The first way - although usable as a good reference mode - requires another high-performance propulsion system.
The second way is ruled out in the present case of σ = 2 g/m²; as a matter of fact, a small α < 0 entails a λr too high and a negative λt too low in absolute value: the sailcraft would go far from the Sun with a decreasing speed (as discussed above).
In the third way, there is a critical negative sail-axis angle in HOF, say, αcr such that for sail orientation angles α < αcr the sailcraft trajectory is characterized as follows:
  1. the distance (from the Sun) first increases, achieves a local maximum at some point M, then decreases. The orbital angular momentum (per unit mass), say, H of the sailcraft decreases in magnitude. It is suitable to define the scalar H = H•k, where k is the unit vector of the HIF Z-axis;
  2. after a short time (few weeks or less, in general), the sailcraft speed V = |V| achieves a local minimum at a point P. H continues to decrease;
  3. past P, the sailcraft speed increases because the total vector acceleration, say, A begins by forming an acute angle with the vector velocity V; in mathematical terms, dV / dt = A • V / V > 0. This is the first key-point to realize;
  4. eventually, the sailcraft achieves a point Q where H = 0; here, the sailcraft's total energy (per unit mass), say, E (including the contribution of the solar pressure on the sail) shows a (negative) local minimum. This is the second key-point;
  5. past Q, the sailcraft - keeping the negative value of the sail orientation - regains angular momentum by reversing its motion (that is H is oriented down and H < 0). R keeps on decreasing while dV/dt augments. This is the third key-point;
  6. the sailcraft energy continues to increase and a point S is reached where E=0, namely, the escape condition is satisfied; the sailcraft keeps on accelerating. S is located before the perihelion. The (negative) H continues to decrease;
  7. if the sail attitude α has been chosen appropriately (about -25.9 deg in this example), the sailcraft flies-by the Sun at the desired (0.2 AU) perihelion, say, U; however, differently from a Keplerian orbit (for which the perihelion is the point of maximum speed), past the perihelion, V increases further while the sailcraft recedes from the Sun.
  8. past U, the sailcraft is very fast and pass through a point, say, W of local maximum for the speed, since λ < 1. Thus, speed decreases but, at a few AU from the Sun (about 2.7 AU in this example), both the (positive) E and the (negative) H begin a plateau or cruise phase; V becomes practically constant and, the most important thing, takes on a cruise value considerably higher than the speed of the circular orbit of the departure planet (the Earth, in this case). This example shows a cruise speed of 14.75 AU/yr or 69.9 km/s. At 100 AU, the sailcraft speed is 69.6 km/s.

H-reversal Sun flyby trajectory

The figure below shows the mentioned sailcraft trajectory. Only the initial arc around the Sun has been plotted. The remaining part is rectilinear, in practice, and represents the cruise phase of the spacecraft. The sail is represented by a short segment with a central arrow that indicates its orientation. Note that the complicate change of sail direction in HIF is very simply achieved by a constant attitude in HOF. That brings about a net non-Keplerian feature to the whole trajectory.

In science fiction

One of the earliest stories about light sails, possibly the earliest, is "The Lady Who Sailed the Soul" by Cordwainer Smith, which was published in 1960. In it, a tragedy results from the slowness of interstellar travel by this method. Another example is the 1962 story "Gateway to Strangeness" (also known as "Sail 25") by Jack Vance, in which the outward direction of propulsion poses a life-threatening dilemma. Also in early 20th century literature, Pierre Boulle's Planet of the Apes starts with a couple floating in space on a ship propelled and maneuvered by light sails. In Larry Niven and Jerry Pournelle's The Mote in God's Eye, a sail is used as a brake and a weapon. Author and scientist Arthur C. Clarke depicted a "yacht race" between solar sail spacecraft in the 1964 short story "Sunjammer". In "Flight of the Dragonfly", Robert Forward (who also proposed the microwave-pushed Starwisp design) described an interstellar journey using a light driven propulsion system, wherein a part of the sail was broken off and used as a reflector to slow the main spacecraft as it approached its destination. In the 1982 film Tron, a "Solar Sailer" was a inner spacecraft with butterfly like sails moved along focused beam of light. In the episode "Explorers" of Star Trek: Deep Space Nine that aired in 1995, a "light ship" was featured. It was designed to use solar wind to fly out of a solar system with no engine.[49] In the film Star Wars Episode II: Attack of the Clones one is used by Count Dooku to propel himself across space. A solar sail was also used in James Cameron's Avatar. In the Disney film Treasure Planet, Solar sails are used literally as sails for interstellar travel of steam-punk styled -masted sailing ship capable of traveling through space.

See also

References

  1. ^ Hsu, Jeremy (21 July 2010). "Japan's Solar Sail Is the Toast of Space Science". Space.com. http://www.space.com/news/solar-sail-exploration-hailed-100721.html. Retrieved 18 August 2010. "first vehicle to have deployed a solar sail and successfully rode the sunlight in deep space." 
  2. ^ Hollerman, William Andrew. "The Physics of Solar Sails". NASA Faculty Fellowship Program. Marshall Space Flight Center. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030093608_2003101292.pdf. Retrieved 17 July 2011. 
  3. ^ [1] http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html
  4. ^ when E is equal to the photon's energy, p is equal to the momentum, and c is the speed of light.
  5. ^ Marcelo Alonso, Edward J. Finn: Fundamental University Physics, Volume II Fields and Waves, Addison-Wesley 1967 (Ninth printing 1978) Library of Congress Catalog Card Number 66-10828; section 19.3 Energy and Momentum in an Electromagnetic Wave. This source cites the number 4.7*10-6 J m-3, based on the less precise 1.4×103W m-2 for the incident energy.
  6. ^ P. Lebedev, 1901, "Untersuchungen über die Druckkräfte des Lichtes", Annalen der Physik, 1901
  7. ^ Lee, Dillon (2008). "A Celebration of the Legacy of Physics at Dartmouth". Dartmouth Undergraduate Journal of Science. Dartmouth College. http://dujs.dartmouth.edu/spring-2008-10th-anniversary-edition/what-else-has-happened-a-celebration-of-the-legacy-of-physics-at-dartmouth. Retrieved 2009-06-11. 
  8. ^ Nicole Meyer-Vernet: How Does the Solar Wind Blow? A Simple Kinetic Model. http://www.lesia.obspm.fr/perso/nicole-meyer/papiers/ejpwind.pdf
  9. ^ In space, aerodynamic and other frictions are absent, and any force will continue to add to the speed; See Newton's first law in any physics text.
  10. ^ Jerome Wright (1992), Space Sailing, Gordon and Breach Science Publishers , chapter 1
  11. ^ Wright, ibid., chapter 2
  12. ^ Forward, R.L. (1984). "Roundtrip Interstellar Travel Using Laser-Pushed Lightsails". J Spacecraft 21 (2): 187–195. Bibcode 1984JSpRo..21..187F. doi:10.2514/3.8632. 
  13. ^ Keith Lofstrom (2002). "Launchloop's discussion of launch altitudes". Archived from the original on 2008-04-14. http://web.archive.org/web/20080414002533/http://www.launchloop.com/isdc2002energy.pdf. 
  14. ^ Wright, ibid., p71, last para
  15. ^ a b Drexler, K.E. (1977). "Design of a High Performance Solar Sail System, MS Thesis,". Dept. of Aeronautics and Astronautics, Massachusetts Institute of Techniology, Boston. http://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741.pdf?sequence=1. 
  16. ^ a b c d e "Design & Construction". NASA JPL. Archived from the original on 2005-03-11. http://web.archive.org/web/20050311004606/http://solarsails.jpl.nasa.gov/introduction/design-construction.html. 
  17. ^ a b Khayatian, Rahmatsamii, Porgorzelski, UCLA and JPL. "An Antenna Concept Integrated with Future Solar Sails". http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/12275/1/01-0276.pdf. 
  18. ^ NASA. "Solar Sails Could Send Spacecraft 'Sailing' Through Space". http://www.space.fmi.fi/~pjanhune/Esail/. 
  19. ^ Zubrin & Andrew's presentation in a pdf.
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Bibliography

External links