Solar Sails

7/18/2019 Solar Sails

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TECHNICAL LECTURE REPORT ON

SOLAR SAILS

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GUIDE’S OBSERVATION:

HOF (L)’S OBSERVATION:



CONTENTS

SL NO CHAPTER PAGE NO

01 Introduction to Solar Sails 4

02 History

0! Pr"s"nt Sc"nario #

04 Princi$l" o% Solar Sails &

0' Construction o% Solar Sails 11

0 (or)in* o% Solar Sails 12

0+ Ca$a,ility 1

0# A$$lications 1#

0& Conclusion 21

10 R"%"r"nc"s 22

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CHAPTER 1

INTRO-UCTION TO SOLAR SAILS

1.1 Introduction.Harnessing the power of the Sun to propel a spacecraft may appear somewhat ambitious and

the observation that light exerts a force contradicts everyday experiences. However, it is and

accepted phenomenon that the quantum packets of energy which compose Sunlight, that is to

say photons, perturb the orbit attitude of spacecraft through conservation of momentum; this

perturbation is known as solar radiation pressure S!"#. $o be exact, the momentum of the

electromagnetic energy from the Sun pushes the spacecraft and from %ewton&s second law

momentum is transferred when the energy strikes and when it is reflected. $he concept of solar

sailing is thus the use of these quantum packets of energy, i.e. S!", to propel a

spacecraft,potentially providing a continuous acceleration limited only by the lifetime of the sail

materials in the space environment. $he momentum carried by individual photons is extremely

small; at best a solar sail will experience ' % of force per square kilometre of sail located in (arth

orbit )c*nnes, 1'''#, thus to provide a suitably large momentum transfer the sail is required to

have a large surface area while maintaining as low a mass as possible.

+dding the impulse due to incident and reflected photons it is found that the idealised thrust

vector is directed normal to the surface of the sail, hence by controlling the orientation of the sail

relative to the Sun orbital angular momentum can be gained or reduced. sing momentum change

through reflecting such quantum packets of energy the sail slowly but continuously accelerates to

accomplish a wide-range of potential missions.

1. Solar sails also called light sails or photon sails# are a form of spacecraft propulsion using

the radiation pressure also called solar pressure# from stars to push large ultra-thin mirrors to

high speeds. /ight sails could also be driven by energy beams to extend their range of

operations, which is strictly beam sailing rather than solar sailing.

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Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes.

Since they have few moving parts and use no propellant, they can potentially be used numerous

times for delivery of payloads. Solar sails use a phenomenon that has a proven, measured effect on spacecraft. Solar pressure

affects all spacecraft, whether in interplanetary space or in orbit around a planet or small body. +

typical spacecraft going to )ars, for example, will be displaced by thousands of kilometres by

solar pressure, so the effects must be accounted for in tra0ectory planning, which has been done

since the time of the earliest interplanetary spacecraft of the 1'2s. Solar pressure also affects

the attitude of a craft, a factor that must be included in spacecraft design. $he total force exerted on an 322 by 322 meter solar sail, for example, is about 4 newtons 1.1

lbf# at (arth5s distance from the Sun,67 making it a low-thrust propulsion system, similar to

spacecraft propelled by electric engines.

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1.8 Conc"$t. Solar !adiation "ressure

Solar radiation exerts a pressure on the sail due to reflection and a small fraction that is

absorbed. $he absorbed energy heats the sail, which re-radiates that energy from the front and

rear surfaces.$he momentum of a photon or an entire flux is given by p 9 (:c, where ( is the photon or flux

energy, p is the momentum, and c is the speed of light. Solar radiation pressure is calculated on an

irradiance solar constant# value of 181 :m at 1 + (arth-Sun distance#, perfect absorbance<

= 9 >.4> ?% per square metre >.4> ?"a# perfect reflectance< = 9 '.23 ?% per square metre

'.23 ?"a# normal to surface#

+ perfect sail is flat and has 122@ specular reflection. +n actual sail will have an overall efficiency

of about '2@, about 3.1A ?%:m, due to curvature billow#, wrinkles, absorbance, re-radiation from

front and back, non-specular effects, and other factors.

=orce on a sail results from reflecting the photon flux

$he force on a sail and the actual acceleration of the craft vary by the inverse square of distance

from the Sun unless close to the Sun#, and by the square of the cosine of the angle between the

sail force vector and the radial from the Sun, so

= 9 =2 cos B : ! ideal sail#

where ! is distance from the Sun in +. +n actual square sail can be modelled as<

= 9 =2 2.8>' C 2. cos B D 2.211 cos >B# : !

%ote that the force and acceleration approach Eero generally around B 9 2F rather than '2Fas one

might expect with an ideal sail.

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https://en.wikipedia.org/wiki/Pressure

https://en.wikipedia.org/wiki/Photon

https://en.wikipedia.org/wiki/Solar_constant

https://en.wikipedia.org/wiki/Astronomical_unit

https://en.wikipedia.org/wiki/Pascal_(unit)

https://en.wikipedia.org/wiki/Specular_reflection

https://en.wikipedia.org/wiki/File:Sail-Force1.gif

https://en.wikipedia.org/wiki/Pressure

https://en.wikipedia.org/wiki/Photon

https://en.wikipedia.org/wiki/Solar_constant

https://en.wikipedia.org/wiki/Astronomical_unit


https://en.wikipedia.org/wiki/Specular_reflection



Solar wind, the flux of charged particles blown out from the Sun, exerts a nominal dynamic

pressure of about 8 to > n"a, three orders of magnitude less than solar radiation pressure on a

reflective sail.

Sail "arameters

Sail loading areal density# is an important parameter, which is the total mass divided by the sailarea, expressed in g:m. *t is represented by the Greek letter .

+ sail craft has a characteristic acceleration, ac, which it would experience at 1 + when facing the

Sun. sing the value from above of '.23 ?% per square metre of radiation pressure at 1 +, ac is

related to areal density by<ac 9 '.23efficiency# : mm:s

+ssuming '2@ efficiency, ac 9 3.1A : mm:s$he lightness number, I, is the dimensionless ratio of maximum vehicle acceleration divided by the

Sun5s local gravity. sing the values at 1 +<

I 9 ac : 4.'8$he 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. $herefore, this number defines

the types of orbit maneuvers that are possible for a given vessel.$he table presents some example values. "ayloads are not included. $he first two are from the

detailed design effort at J"/ in the 1'A2s. $he third, the lattice sailer, might represent about the

best possible performance level. $he dimensions for square and lattice sails are edges. $he

dimension for heliogyro is blade tip to blade tip.

Ty$" .

/*2ac/s2 3

Si"

/)

Square sail 4.A 1.4 2. 2.32

Heliogyro .8' 1.' 2. 14

/attice sailer 2.2A 11A 2 1

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https://en.wikipedia.org/wiki/Solar_wind


https://en.wikipedia.org/wiki/Solar_wind




CHAPTER 2

HISTOR5

.1 Johannes Kepler observed that comet tails point away from the Sun and suggested that the

Sun caused the effect. *n a letter to Galileo in 112, he wrote, L"rovide ships or sails adapted to

the heavenly breeEes, and there will be some who will brave even that void.L 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.

James Mlerk )axwell, in 131N>, published his theory of electromagnetic fields and radiation,

which shows that light has momentum and thus can exert pressure on ob0ects. )axwell5s

equations provide the theoretical foundation for sailing with light pressure. So by 13>, the physics

community and beyond knew sunlight carried momentum that would exert a pressure on ob0ects.

. Jules Oerne, in =rom the (arth to the )oon, published in 134, wrote Lthere will some day

appear velocities far greater than these 6of the planets and the pro0ectile7, of which light or

electricity will probably be the mechanical agent, we shall one day travel to the moon, the planets,

and the stars.L $his is possibly the first published recognition that light could move ships through

space. Given the date of his publication and the widespread, permanent distribution of his work, it

appears that he should be regarded as the originator of the concept of space sailing by lightpressure, although he did not develop the concept further6original research. Oerne probably got the

idea directly and immediately from )axwell5s 13> theory although it cannot be ruled out that

)axwell or an intermediary recogniEed the sailing potential and became the source for Oerne#.

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+lbert (instein provided a different formalism by his recogniEing the equivalence of mass and

energy. He simply wrote p 9 (:c as the relationship between the momentum, the energy, and the

speed of light.

$he first formal technology and design effort for a solar sail began in 1'A at Jet "ropulsion

/aboratory for a proposed mission to rendeEvous with Halley5s Mome

CHAPTER !

PRESENT SCENARIO

8.1 =ollowing the Momet Halley studies solar sailing entered a hiatus until the early 1''2&s

when further advances in spacecraft technology led to renewed interest in the concept. $he first

ever ground deployment of a solar sail was performed in KPln in Qecember 1''' by the

German space agency, Q/!, in association with (S+ and *%O(%$ GmbH when they deployed a

square 2-m solar sail, shown in =ig. 1 /eipold et al, 222; Sebolt et al, 222#.

$his ground deployment and the associated technology developed by Q/! and (S+ has

struggled to progress to flight, initially an in-orbit deployment was planned for 22 however this

pro0ect floundered, with a similar, but smaller, demonstration now planned for 218 as part of a

three-step solar sail technology development program /ura et al, 212#.

*n 224 %+S+ completed dual solar sail development programs, funding a solar sail design by

+$K and another by /&Garde *nc. who used the inflatable boom technology developed under the

*+( program. Roth solar sail systems were deployed to 2-m side length# in the large vacuum

chamber at %+S+ Glenn !esearch Menter5s Space "ower =acility at "lum Rrook Station in

Sandusky, hio, .S.+, the world5s largest vacuum chamber /ichodEie0ewski et al, 228;

)urphy et al, 228 T 22>#.

=ollowing the deployment demonstrations the /&Garde design was down-selected due to its

perceived scalability to much larger sail siEes for the subsequent %+S+ %ew )illennium Space

$echnology ' S$-'# proposal, prior to the S$-' program being cancelled. However, it should be

noted that the +$K sail was considered a lower risk option. $he intention of the %+S+ funding

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was to develop solar sail technology to $echnology !eadiness /evel $!/# six, however a

subsequent assessment found that actually both the /&Garde and +$K sail failed to fully achieve

either $!/ 4 or , with the +$K sail achieving 3'@ and 3@, respectively and the /&Garde sail

reaching 3> @ and A3 @, respectively Uoung et al, 22A#.

*n )ay 212 the first spacecraft to use solar radiation pressure as its primary form of propulsion

was launched by the Japanese space agency, J+V+, onboard an H-**+ launch vehicle from the

$anegashima Space Menter as an auxiliary payload alongside the Japanese Oenus orbiter

+katsuki, formerly known as the Oenus Mlimate rbiter OM# and "lanet-M,and four micro-

spacecraft. $he solar sail spacecraft is called *K+!S *nterplanetary Kite-craft +ccelerated by

!adiation f the Sun# and like the +katsuki spacecraft was launched onto a near-Oenus transfer

tra0ectory. $he *K+!S is a square solar sail, deployed using spinning motion and 2.4 kg tip

masses, the polyimide film used for solar sailing also has thin-film solar arrays embedded in the

film for power generation and liquid crystal devises which can, using electrical power, be

switched from diffusely to specularly reflective for attitude control )oriet al, 212#. *K+!S has

demonstrated a propulsive force of 1.1m% )ori et al, 212# and is shown in =ig. 8. $he

*K+!S mission is envisaged as a technology demonstrated towards a power sail spacecraft,

using the large deployable structure to host thin-film solar cells to generate large volumes of

power to drive a S(" system Kawaguchi, 212#.

*n addition to the traditional view of solar sailing as a very large structure several organisations,

including %+S+ and the "lanetary Society, are developing MubeSat based solar sails. *ndeed,

%+S+ flew the first MubeSat solar sails on board the third SpaceV =alcon1 launch on +ugust

223 which failed approximately minutes after launch. *t is however unclear how such

MubeSail programs will complement traditional solar sailing and whether they will provide

sufficient confidence in the technology to enable larger, more advanced solar sail demonstrator

missions. *t is clear that the technology of solar sailing is beginning to emerge from the drawing

board. +dditionally, since the %+S+ Momet Halley mission studies a large number of solar sail

mission concepts have been devised and promoted by solar sail proponents. +s such, thisrange of mission applications and concepts enables technology requirements derivation and a

technology application pull roadmap to be developed based on the key features of missions

which are enabled, or significantly enhance, through solar sail propulsion. $his book chapter will

thus attempt to link the technology application pull to the current technology developments and

to establish a new vision for the future of solar sailing.

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CHAPTER 4

PRINCIPLE O6 SOLAR SAILS

>.1 $he direction and the magnitude of the solar radiation pressure are depending on the

distance between sun and sail as well as the sail attitude. $he orbital dynamics of solar sailcraft is

in many respects similar to the orbital dynamics of other spacecraft, where a small continuous

thrust is applied to modify the spacecraft5s orbit over an extended period of time. However, other

continuous thrust spacecraft e.g. using electric propulsion# may orient its thrust vector into any

desired direction and vary its thrust level within a wide range, whereas the thrust vector of a solar

sail is constrained to lie on the surface of a Wbubble& directed away from the sun. %evertheless, by

controlling the sail orientation relative to the sun, solar sailcraft can gain orbital angular momentumand spiral outwards N away from the sun N or lose orbital angular momentum and spiral inwards N

towards the sun.

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CHAPTER '

CONSTRUCTION O6 SOLAR SAILS

4.1 Solar Sail 7at"rials

hile solar sails have been designed before %+S+5s had a solar sail program back in the 1'A2s#,

materials available until the last decade or so were much too heavy to design a practical solar

sailing vehicle. Resides being lightweight, the material must be highly reflective and able to tolerate

extreme temperatures. $he giant sails being tested by %+S+ today are made of very lightweight,

reflective material that is upwards of 122 times thinner than an average sheet of stationery. $his

LaluminiEed, temperature-resistant materialL is called M"-1. $he reflective nature of the sails is key. +s photons light particles# bounce off the reflective material, they gently push the sail along by

transferring momentum to the sail. Recause there are so many photons from sunlight, and

because they are constantly hitting the sail, there is a constant pressure force per unit area#

exerted on the sail that produces a constant acceleration of the spacecraft. +lthough the force on a

solar-sail spacecraft is less than a conventional chemical rocket, such as the space shuttle, the

solar-sail spacecraft constantly accelerates over time and achieves a greater velocity.Uou might be

wondering what happens when the spacecraft finds itself far from sunlight. +n onboard laser could

take over providing the necessary propulsion to the sails.

$he material developed for the Qrexler solar sail was a thin aluminium film with a baseline

thickness of 2.1 Xm, to be fabricated by vapor deposition in a space-based system. Qrexler used a

similar process to prepare films on the ground. +s anticipated, these films demonstrated adequate

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strength and robustness for handling in the laboratory and for use in space, but not for folding,

launch, and deployment.

$he most common material in current designs is aluminiEed Xm Kapton film. *t resists the heat of

a pass close to the Sun and still remains reasonably strong. $he aluminium reflecting film is on the

Sun side. $he sails of Mosmos 1 were made of aluminiEed "($ film )ylar#.

$here 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 LspacesL are less than half the wavelength of light impinging on the sail. hile 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 2.1 g:m, making them lighter than any current sail material by a factor of at least

82. =or comparison, 4 micrometre thick )ylar sail material mass A g:m, aluminiEed Kapton films

have a mass as much as 1 g:m, and (nergy Science /aboratories5 new carbon fiber material

masses 8 g:m.

$he least dense metal is lithium, about 4 times less dense than aluminium. =resh, unoxidiEed

surfaces are reflective. +t a thickness of 2 nm, lithium has an areal density of 2.211 g:m. + high-

performance sail could be made of lithium alone at 2 nm no emission layer#. *t would have to be

fabricated in space and not used to approach the Sun. *n the limit, a sail craft might be constructed

with a total areal density of around 2.2 g:m, giving it a lightness number of A and ac of about

>22 mm:s. )agnesium and beryllium are also potential materials for high-performance sails.

$hese 8 metals can be alloyed with each other and with aluminium.

'82 R"%l"cti9" and Eissi9" lay"rs : +luminium is the common choice for the reflection layer. *t

typically has a thickness of at least 2 nm, with a reflectivity of 2.33 to 2.'2. Mhromium is a good

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choice for the emission layer on the face away from the Sun. *t can readily provide emissivity

values of 2.8 to 2.A8 for thicknesses from 4 to 2 nm on plastic film. sable 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.

'8! 6a,rication

Sails are fabricated on (arth on long tables where ribbons are unrolled and 0oined to create the

sails. $hese sails are packed, launched, and unfurled in space.

*n the future, fabrication could take place in orbit inside large frames that support the sail. $his

would result in lower mass sails and elimination of the risk of deployment failure.

CHAPTER

(OR;ING O6 SOLAR SAIL

81 C<an*in* or,its

Sailing operations are simplest in interplanetary orbits, where attitude changes are done at low

rates. =or outward bound tra0ectories, 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. =or inward tra0ectories, 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.

*t is worth noting that only the Sun5s gravity pulls the craft toward the SunYthere is no analog to a

sailboat5s tacking to windward. $o change orbital inclination, the force vector is turned out of the

plane of the velocity vector.

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*n 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.

$ra0ectory optimiEations can often require intervals of reduced or Eero thrust. $his 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.

82 S=in*>,y 7an"u9"rs

+ close solar passage can be used to increase a craft5s energy. $he increased radiation pressure

combines with the efficacy of being deep in the Sun5s gravity well to substantially increase the

energy for runs to the outer Solar System. $he optimal approach to the Sun is done by increasing

the orbital eccentricity while keeping the energy level as high as practical. $he 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#. + close passage can result

in substantial optical degradation. !equired turn rates can increase substantially for a close

passage. + 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.

+ lunar swing-by can have important benefits for tra0ectories leaving from or arriving at (arth. $his

can reduce trip times, especially in cases where the sail is heavily loaded. + swing-by can also be

used to obtain favorable departure or arrival directions relative to (arth.

+ 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 optimiEation of the tra0ectory.

8! Sart lin"s

+ smart line could be a critical element of sailing operations. +s with maritime ships, lines are

essential for a wide range of uses. ne difference is that some lines may be very long and need tobe self-guiding. $he lines could extend from and retract into the sail craft.

+ maneuverable grappling device can be used at the end of a line to place or pick up payload

containers, to secure a ship to a structure such as a station, to pick up samples from an asteroid or

comet, or to engage in towing. $he maneuvering unit is like a small spacecraft, with many of the

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same sensors and control systems. *t could draw power from and communicate with the sail craft

through the line. $hese operations could be done autonomously.

/ines a few hundred kilometers long may be used to move a ship from a space station to an orbit

farther out where it could begin sailing.

84 To=in*

Smart lines can enable towing operations by being able to attach to or release ob0ects at the

remote end of the line. +ttached ob0ects might be pulled in to the body of the sailer or remain at the

end of the deployed line. b0ects to be towed may have attachment points that allow multiple sail

craft to engage in the towing. $owing operations can include deflecting large bodies that pose a

haEard to (arth, bringing natural bodies to (arth or other sites for resource recovery, and

transporting disabled spacecraft or other structures.

$o tow or deflect a large body, poles can be inserted on the spin axis of the body. Sail craft can

attach to the embedded poles using smart lines. Slip rings enable the craft to tow without the lines

getting wrapped up as a result of rotation of the body.

CHAPTER +

CAPA?ILIT5

A.1 ;"y c<aract"ristics

Solar sailing has traditionally been perceived as an enabling technology for high-energy emissions;

however, as has been shown in the preceding sections the key characteristics of a mission which

is enabled, or significantly enhanced by solar sailing are more complex than simply this. Solar

sailing is, due to the lack of propellant mass, often noted as reducing the launch mass of an

equivalent chemical or S(" concept, which is in-turn noted as reducing launch and emission cost.

However, while it is accurate that the launch mass is typically reduced this does not directly result

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in a reduced launch vehicle cost as the reduction may not be sufficient to allow the use of a less

capable, and hence lower cost, launch vehicle. +s such the launch cost is only reduced if the

reduced launch mass allows a smaller launch vehicle to be used, meaning that launch cost varies

as a step function while launch mass linearly increases. =inally, it should be noted that if the total

mission cost is high, say, 422C )Z then reducing the launch mass cost by 12 N 2 )Z is a cost

saving of order N > @, which may not be considered a good cost:risk ratio for the pro0ect and

indeed, the cost saving may be insufficient to pay for the additional development of the technology.

$hus for the reduction in launch mass to be an enabling, or significantly enhancing aspect of a

solar sail mission concept the cost saving must also be a significant percentage of the total

mission cost. +ll solar sail mission concepts can be sub-divided into two classes, these are<

[ Mlass ne

here the solar sail is used to reach a high-energy target and after which the sail can be

0ettisoned by the spacecraft, for example the Solar "olar rbiter mission.

[ Mlass $wo

here the solar sail is required to maintain a novel or otherwise unsustainable observation

outpost, for example, highly non-keplerian or non-inertial orbit applications, such as Geostorm and

GeoSail.

$his distinction is important as the later compares very favourably against most other propulsion

systems, especially as the mission duration and hence reaction mass is increased.

However, a solar sail is a very large structure and could adversely impact the mission ob0ectives

either through a characteristically low pointing accuracy due to low frequency structural flexing, or

due to the solar sail interfering with the local environment in, for example, particle and field

measurements. $hus, a critical requirement on early solar sail demonstration missions must be to

validate the simulated pointing accuracy of the platform and the effect of the sail on the local space

environment.

=rom the mission catalogue it is seen that solar sail propulsion has been considered for a large

range of mission applications, some of which it is more suitable for than others. (ach of the solar sail applications within the mission catalogue are sub-divided by the level of enhancement offered

by solar sail propulsion.

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CHAPTER #

APPLICATIONS

3.1 "lanet-centred and other short orbit period applications.

$his category is essentially planet, minor-planet and small body centred tra0ectories.

"lanet centered tra0ectory design has been largely restricted to escape manoeuvres or relatively

simplistic orbit manoeuvring, such as lunar fly-by&s or orbit inclination change. Such tra0ectories

place significant technology demands on the solar sail architecture, for example a locally optimal

energy gain control profile for an (arth-centered orbit requires the sail to be rotated through 132

degrees once per orbit and then rapidly reset to maximise energy gain; as the sail siEe grows

clearly this becomes an increasingly demanding technology requirement.

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3. Highly non-keplerian orbit applications.

$his category is, in some regards, an extension of the concept embodied by non-inertial

orbits, with the sail providing a small but continuous acceleration to enable an otherwise

unattainable or unsustainable observation outpost to be maintained. $wo primary solar sail

applications of Highly %Ks are found in the literature; Geostorm and "olesitter also called "olar

bserver# Riggs T )c*nnes, 22'; Mhen-wan, 22>; Qriver, 1'32; =orward, 1''1; )atloff, 22>;

)c*nnes et al, 1''>; Sauer, Jr., 22>; aters T )c*nnes, 22A; est, 1'', 222, 22>#. $he

Geostorm mission concept provides real-time monitoring of solar activity; the spacecraft would

operate sunward of the (arth&s /1 point, thus increasing the warning time for geomagnetic storms.

Ry imparting a radial outward force from the Sun the solar radiation pressure in-effect reduces

solar gravity and allows the /1 point to be moved sunward. +s sail performance is increased solar

gravity is further Wreduced&, thus providing enhanced solar storm warning.

$he "olesitter concept extends the Geostorm concept from a singular equilibrium point to

derive equilibrium surfaces which extend out of the ecliptic plane and are again parameterised by

the sail performance )c*nnes et al, 1''>#. Ry extending the artificial equilibrium points out of the

ecliptic plane, the small but continuous acceleration allows a spacecraft to be stationed above, or

below, the second body within the 8-body problem. + further example of a highly non-keplerian

orbit application is the Statite proposed by =orward 1''1#, which would use a high-performance

solar sail to directly balance the solar gravity to hover stationary over the poles of the Sun.

3.8 *nner solar system rendeEvous missions

$his category covers missions which use the solar sail to rendeEvous, and perhaps bound

the orbit to, a body in the inner solar system; defined as all bodies from the asteroid belt inwards,

specifically excluding bodies which are, in-effect, part of the Jupiter system, for example the Hilda

and Jupiter $ro0an asteroids. Solar sailing, like other forms of low-thrust propulsion ,requires that if

a bound orbit about the target body is desired then at arrival the spacecraft must have, in-effect,

Eero hyperbolic excess velocity. $herefore, any wholly low-thrust interplanetary mission is required,unlike high-thrust missions, to slow-down prior to arrival at the target body and subsequently the

transfer duration is typically significantly increased; this is especially true for bodies which can be

relatively easily reached by high-thrust, chemical propulsion systems such as )ars and Oenus.

=urthermore, once the solar sail has been captured into a bound-orbit about the target body it then

has the typical disadvantages discussed previously for planet-centred solar sail application

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3.> uter solar system rendeEvous missions

$he use of solar sails for outer solar system rendeEvous missions has been long discussed within

the literature Garner et al, 221; /eipold, 1'''; right, 1''; right T armke,1'A#.

=urthermore, an assessment study was previously conducted by the +uthors and Hughes looking

at a range of solar sail Jupiter missions )c*nnes et al, 228e, 22>a#, including concepts for

exploration of the Galilean moons. +s with low-thrust inner solar system rendeEvous missions the

hyperbolic excess velocity at the target outer solar system body must be lower than high-thrust

missions. $he inverse squared variation in S!" with solar distance however means that the sail

performance is significantly reduced over the same sail at (arth. +s such the requirement to

reduce the hyperbolic excess velocity prior to arrival at the outer solar system body leads to

prolonged transfer durations

3.4 uter solar system flyby missions

uter solar system fly-by missions remove the requirement to reduce the hyperbolic excess

velocity prior to arrival at the target body and as such negate much of the negative elements of

solar sail outer solar system rendeEvous missions. + Jupiter atmospheric probe mission was

considered by the +uthors and Hughes )c*nnes et al, 228e# as a potential Jupiter flyby mission.

*t was concluded that due to the mass of the atmospheric probes, of which three were required,

and the relative ease of such a mission with chemical propulsion that solar sail propulsion offered

little to such a mission. *t is of note that as the target flyby body moves further from the Sun,

3. Solar missions

$he lysses spacecraft used a Jupiter gravity assist to pass over the solar poles, obtaining field

and particle measurements but no images of the poles. =urthermore, the lysses orbit is highly

elliptical, with a pole revisit time of approximately years. *t is desired that future solar analysis be

performed much closer to the sun, as well as from an out-of-ecliptic perspective. $he MosmicOisions mission concept Solar rbiter intends to deliver a science suite of order 132 kg to a

maximum inclination of order 84 deg with respect to the solar equator and to a minimum solar

approach radius of 2. au using S(". $he inability of the Solar rbiter mission to attain a solar

polar orbit highlights the difficulty of such a goal with conventional propulsion.

21



3.A Reyond %eptune

*t has been shown that solar sail propulsion offers significant benefits to missions concepts which

aim to deliver a spacecraft beyond %eptune, for either a Kuiper Relt or *nterstellar Heliopause at

approximately 22 au# mission. Such outer solar system missions initially exploit the inverse

squared variation in S!" with solar distance by approaching the Sun to gain a rapid energy boast

which generates a hyperbolic tra0ectory and allows the spacecraft to rapidly escape the solar

system. Solar sails mission concepts significantly beyond the *nterstellar Heliopause were

considered by )acdonald et al 212#. *n-order to determine the limit of the solar sail concept an

ort cloud mission was examined using solely S!" to propel the spacecraft. *t was found that

although no fundamental reason existed why such a mission may not be possible the practicalities

were such that the *nterstellar Heliopause "robe *H"# mission concept could be considered

representative of the upper limiting bound of the solar sail concept.

22



CHAPTER &

CONCLUSION

'.1

+ solar sail mission catalogue has been developed and presented. $he mission catalogue

was sub-divided into applications which were enabled, or significantly enhanced by solar

sailing, of which solar sailing is of marginal benefit and of which solar sailing could

beconsidered unconstructive. =rom this the key characteristics of solar sail enabled,

orsignificantly enhanced, missions were detailed prior to a detailed discussion of three key

applications of solar sailing and the presentation of a solar sail application pull technology

development roadmap. Monsidering the solar sail application pull technology development

roadmap it was noted that the near-term was sparsely populated, with the significantma0ority of applications clustered in the mid to far term. $he concept of a system level

+dvancement Qegree of Qifficulty was introduced and it was illustrated that how through, for

example, hybridisation with solar electric propulsion the pro0ect risk of solar sailing could be

reduced while simultaneously.

23



CHAPTER 10

RE6ERENCES

1. Georgevic, !. ). 1'A8# L$he Solar !adiation "ressure =orces and $orques )odelL, $he

Journal of the +stronautical Sciences, Ool. A, %o. 1, JanN=eb. =irst known publication

describing how solar radiation pressure creates forces and torques that affect

spacecraft.

. Jerome right 1''#, Space Sailing, Gordon and Rreach Science "ublishers

8. Jump up\ =riedrich ]ander5s 1'4 paper, L"roblems of flight by 0et propulsion<

interplanetary flightsL, was translated by %+S+. See %+S+ $echnical $ranslation =-1>A

1'>#

>. LQesign of a High "erformance Solar Sail System, )S $hesis,L "Q=#. Qept. of

+eronautics and +stronautics, )assachusetts *nstitute of $echniology, Roston.

4.

24

Solar Sails

Documents