Around the Sun Without a Sail

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 aerodynamic braking. 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. For Saturn, the minimum trip time is 3. The Sun's inner gravitational focus point lies at minimum distance of AU from the Sun, and is the point to which light from distant objects is 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. It has been proposed that an inflated sail, made of beryllium , that starts at 0. 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. 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. 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.

Minor errors are greatly amplified by gravity assist maneuvers, so using radiation pressure to make very small corrections saved large amounts of propellant. In the s, 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 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.

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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 units 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 [26] [27] 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. 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. Another more physically realistic approach would be to use the light from the Sun to accelerate. 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 system. 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 reentry.

The sail's purpose is to bring the satellite out of orbit over a period of about 25 years. As of , it was still under thrust, proving the practicality of a solar sail for long-duration missions. The sail is made of thin polyimide film, coated with evaporated aluminium. It steers with electrically-controlled 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. 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. The highest thrust-to-mass designs for ground-assembled deploy-able 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 close to the Sun for maximum thrust. Most designs steer with small moving sails on the ends of the spars. In the s JPL studied many rotating blade and ring sails for a mission to rendezvous with 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.

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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 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.

Are Solar Sails the Future of Space Travel?

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. 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. A solar sail can serve a dual function as a high-gain antenna. Pekka Janhunen from FMI has invented a type of solar sail called the electric solar wind sail. The sails are replaced with straightened conducting tethers wires placed radially around the host ship.

The wires are electrically charged to create an 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 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. 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. The polymer provides mechanical support as well as flexibility, while the thin metal layer provides the reflectivity.

Solar Sail Spacecraft Could Explore Beyond Solar System

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. Eric Drexler developed a concept for a sail in which the polymer was removed. His sail would use panels of thin aluminium film 30 to nanometres thick supported by a 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. 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 —, 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.

In , Energy Science Laboratories developed a new carbon fiber material that might be useful for solar sails. 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. The least dense metal is lithium , about 5 times less dense than aluminium. Fresh, unoxidized surfaces are reflective. 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. Magnesium and beryllium are also potential materials for high-performance sails.

These 3 metals can be alloyed with each other and with aluminium. Aluminium is the common choice for the reflection layer. Chromium is a good choice for the emission layer on the face away from the Sun.

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It can readily provide emissivity values of 0. 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. 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. 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. Sailing operations are simplest in interplanetary orbits, where attitude changes are done at low rates.

Your Answer

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.

Sail Across the Sun

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. 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.

The following table lists some example concepts using beamed laser propulsion as proposed by the physicist Robert L. Hayabusa also used solar pressure on its solar paddles as a method of attitude control to compensate for broken reaction wheels and chemical thruster. The trim tab on the solar array makes small adjustments to the torque balance.

NASA has successfully tested deployment technologies on small scale sails in vacuum chambers. On February 4, , the Znamya 2 , a meter wide aluminized-mylar reflector, was successfully deployed from the Russian Mir space station. Although the deployment succeeded, propulsion was not demonstrated.

A second test, Znamya 2. A joint private project between Planetary Society , Cosmos Studios and Russian Academy of Science in made a suborbital prototype test, which failed because of rocket failure. It deployed from the stage, but opened incompletely.

Both sails used 7. The experiment purely tested the deployment mechanisms, not propulsion. The goal was to deploy and control the sail and, for the first time, to determine the minute orbit perturbations caused by light pressure. Until , no solar sails had been successfully used in space as primary propulsion systems. The polyimide sheet had a mass of about 10 grams per square metre. 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. So no zigging, no zagging, using anything like tacking.

Now maybe gravity can be used as another vector via orbital mechanics as Pearson and SF mention, and maybe one day this will be called "tacking" but the physics are wholly different than a keel through water. In some ways an E-sail [made of 20km-long tethers with a positive charge, repelling solar wind particles] resembles a solar sail, a rival idea for powering craft cheaply through space.

A solar sail provides propulsion because the sunlight it reflects exerts pressure on the sail, pushing it forward. But E-sails have an important advantage over solar sails. Once unfurled, there is no easy way to stop a craft with a solar sail gathering speed. An E-sail-powered craft can be prevented from accelerating simply by switching off its electron gun.

This means it can return to Earth under the influence of the sun's gravity. A solar "sail" is basically a mirror. The analogy of wind and sails on ships is not useful for understanding how solar sails work. Each photon from the sun which strikes the sail is reflected. Each photon imparts a small amount of momentum. If the sail is pointed directly at the sun then you get twice the photon's momentum added to the sail.

If you angle the sail, then you are sending each photon off in a direction that is not directly back towards the sun; That gives you a net force to one side. So you can control the vector of the total force of the reflecting photons, but the net direction is always more than 90 degrees from the sun.

As the mirror approaches edge-on to the sun, the net force vector would approach 90 degrees from the sun and drop to zero magnitude. Note that the pressure from the sun's photons applies to anything. It doesn't have to be a designed sail. Orbital mechanics currently take "light pressure" into account for accurate determinations of space craft orbits.

You can use the momentum from the solar sail to alter the orbital eccentricity to move a part of the orbit closer to the sun, etc. If you want to go directly towards the sun from the earth, you don't need a force pushing you directly toward the sun. You need a force pushing against your normal orbital direction. That decreases your angular momentum about the sun, and you then fall towards the sun due to gravity. This is actually somewhat easier than you would think.

So, all you have to do is create a net momentum that pushes to slow down your orbital velocity. However, a big part of what makes tacking work is the fact that you are forcing the water to act as a friction medium against the wind, in essence, causing it to slow you down. I'm not an expert in such motion, but I believe a configuration like below would work, assuring the arrow is the direction of orbital motion, and the sail is the T like item.

The direction could be off by 90 degrees to make this happen, and it might not work really close to the sun, but it should get you in the right direction at least. Travelling towards the sun http: In fact, this has already been done, by a Japanese probe called Ikaros. It sailed using the sun to Venus, from Earth Orbit, and thus demonstrated that this is possible.

While you can't do tricks common for normal sails due to lack of water to keep your keel from drifting sideways and normally lets the ship travel upwind, you are still able to extract force diagonal to the sun radius the angle of incidence equals the angle of reflection; resulting force is perpendicular to the surface , aimed outside the Solar system. Now, this wouldn't let you travel inwards, except That way, despite the parallel component pushing you outside, against the Sun gravity, your orbital speed and resulting centrifugal force drops; and while the outwards component of the solar sail push is only momentary, your orbital speed loss accumulates and leads to continuous reduction of your orbital radius.

Solar sail lets you change orbital speed. Sun gravity can make you travel towards the Sun, depending on said speed. In sailing, tacking is used to sail as close to the wind as you can obviously not straight into it, though the hard wing Americas Cup boat might have been able to while still generating lift in the sail. For normal boats this means at best a degree angle to the wind. Thus you sail a zig zag pattern and need to tack, else you get way off course. Wind sails do not work by pressure of the wind, pushing them, except in straight downwind situations or in older square sail you see in movies about pirates, etc.

Modern sails have curvature and loft and work as vertical wings, generating lift from the pressure differential created by airflow at different speeds over the two sides of the wing. Solar sails do not have that ability, as photons do not act like air molecules in an atmosphere. Thus they need to sail, straight 'down wind' as it were. By using gravity gradient from nearby planets and the Sun.

The sail isn't moving trait out from the Sun. It is also in orbit around the sun as it is moving all the sail would have to do is large body or angle the radiation pressure in the direction of travel to slow its speed to where the Sun's gravity pulls it in. By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies.

Home Questions Tags Users Unanswered. Can you tack against the sun using a solar sail? Not all Ocean going ships are able to tack against the wind. Sails with the proper shapes are needed. Uwe see related sister site question; Do square-riggers also use 'aircraft-wing-style' propulsion?