MEMS and Solar Sail for Space Application

MEMS AND SOLAR SAIL FOR SPACE APPLICATION
ABSTRACT
Micro-Electro-Mechanical system, or MEMS, are integrated micro devices or system combining
electrical and mechanical components. They are fabricated using integrated circuit (IC) batch
processing techniques and can range in size from micrometers to millimeters. These systems can
sense, control anad actuate on the micro scale and function individullay or in arrays to generate
effects on the macro scale. Solar sails (also called light sails or photon sails) are a form of spacecraft
propulation using the radation pressure (solar pressure) from stars to push large ultra-thin mirrors to
high speeds. Solar sail craft offer the possibilty of low cost operations combined with long operating
lifetimes. Since they havve few moving parts and use no propellant, they can potentially be used
numerous times for delivery of pay loads. Solar sails use a phenomenon that has a proven measured
effect on spacecraft. Solar pressure affects all spacecraft whether in interplanelary space or in orbit
around a planet or small body.
Keywords : MEMS, Solar sails, Silicon satellites, Attitude (orientation) control
DEPARTMENT OF ELECTRICAL ENGINEERING 1

CHAPTER 1
MEMS
1.1 What is MEMS
MEMS (Micro Electro Mechanical Systems) is the integration of electrical devices and mechanical
structures at the micrometer (10-6
m = 0.000001 m) scale. The essence of MEMS is their ability to
perform and enhance tasks, in ways and in the micro world, impossible using conventional
technologies. MEMS devices find applications in the automotive, medical, aerospace, defense and
telecommunications industries. Although, electrical devices and very few mechanical devices at this
scale are common, the scaling down of common mechanical devices found in the macro world has
created a research area all its own. The behavior of mechanical structures at the micro scale has yet
to reach full understanding. Although, MEMS are created using many of the fully understood
processing techniques used in IC (Integrated Circuit) processing with little variation, there are still
many material, fabrication and packaging issues that have yet to be resolved. Micro-Electro-
Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and
electronics on a common silicon substrate through micro fabrication technology. While the
electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or
BICMOS processes), the micromechanical components are fabricated using compatible
"micromachining" processes that selectively etch away parts of the silicon wafer or add new
structural layers to form the mechanical and electromechanical devices.
The semiconductor industry already has much of the infrastructure to batch process MEMS devices,
however, the expertise to mass produce a wide variety of MEMS devices is still in its infancy,
stimulated by research funded by both corporations and government agencies. NASA has a very
special interest in MEMS technology. MEMS offer the benefits of significantly reduced mass and
power consumption translating directly into direct cost benefits as a result of this. The main obstacle
in rapidly integrating new technologies into space systems is determining system reliability.
Reliability, the ability of a device/system to maintain performance requirements throughout its
lifetime, is a major consideration factor for making device selections for space flight applications.
Space missions can be expected to last upwards of 5 years with spacecraft subject to extreme
mechanical shock, vibration, and temperature, vacuum, and radiation environments. MEMS promises
to revolutionize nearly every product category by bringing together silicon-based microelectronics
with micromachining technology, making possible the realization of complete systems-on-a-chip.

MEMS is an enabling technology allowing the development of smart products, augmenting the
computational ability of microelectronics with the perception and control capabilities of
microsensors and microactuators and expanding the space of possible designs and applications.
1.2 Types of MEMS devices
MEMS devices can be classified in many ways, however in the broader sense there are only two
types, sensors and actuators. Some devices act as both sensor and actuator. The remaining systems
include individual types or combinations with added electronic circuitry for control
and/or processing information. The three basic types of MEMS devices are:
1. Sensor - converts a nonelectrical input quantity (i.e. pressure, temperature,
acceleration) into an electrical output quantity. Sensors are commonly encountered.
2. Actuator - converts electrical input quantities into non-electrical output quantities.
3. Smart MEMS - MEMS combined with additional electronic circuitry for control and
processing information
Microelectronic integrated circuits can be thought of as the "brains" of a system and MEMS
augments this decision-making capability with "eyes" and "arms", to allow microsystems to sense
and control the environment. Sensors gather information from the environment through measuring
mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then
process the information derived from the sensors and through some decision making capability direct
the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby
controlling the environment for some desired outcome or purpose. Because MEMS devices are
manufactured using batch fabrication techniques similar to those used for integrated circuits,
unprecedented levels of functionality, reliability, and sophistication can be placed on a small silicon
chip at a relatively low cost.
The evolution of microelectomechanical systems (MEMS) from the laboratory curiosities to
commercial off-shelf components (COTS) is being driven by government investments and strong
market forces. MEMS offers a capability for mass production, small, reliable, intelligent instruments
at reduced costs by reducing the number of piece parts, eliminating manual assembly steps and
controlling material variability. These features, together with reduced mass and power requirements
are what space system designer’s dream about.
Space system comprises more than just spacecraft, they include launch vehicles and the ground based
systems used for tracking, command and control and data dissemination (pictures of earth, telephone
calls, movies via satellite etc.) MEMS technology would allow developments of new commercial
uses of space in the proliferation of miniaturized ground transmitters with on board sensors. MEMS,

coupled with the current generation of digital electronics and telecommunication circuits, can be
used for distributed remote sensing applications. For example, transmitters of the size of fist and
smaller can send environmental information such as local atmosphere, pressure, temperature and
humidity, directly to satellite.
MEMS will also enable a radically new way of building and using spacecraft. Silicon, for example
can be used as a multifunctional material: as structure, electronic substrate, MEMS substrate,
radiation shield, thermal control system and optical material. With proper spacecraft design it can
provide these functions simultaneously. A 'silicon' satellite composed of bonded thick wafer could be
manufactured by one or more semiconductor foundries. Batch fabrication would allow mass
production of spacecraft from one hundred to several thousands units which would enable dispersed
satellites architecture and space design meant for single function and disposable missions.

CHAPTER 2
ROLE OF MEMS IN SPACE APPLICATION
MEMS offer the benefits of significantly reduced mass and power consumption, translating directly
into costs benefits as a result of the major decrease in size. There are a number of possibilities for the
insertion of MEMS and ASIM (application specific micro instruments) components into space
hardware. Following are the best estimate of the above technologies that will be inserted in the near
term.
2.1 Command and control systems
i. "MEMtronics" for ultra radiation hard and temperature
ii. insensitive digital logic
iii. On-chip thermal switches for latchup isolation and reset
2.2 Inertial guidance systems
i. Microgyros (rate sensors)
ii. Micro accelerometers
iii. Micromirrors and micro optics for FOGs (fiber-optic gyros)
2.3 Attitude determination and control systems
i. Micromachined sun and Earth sensors
ii. Micromachined magnetometers
iii. Micro thrusters
2.4 Power systems
i. MEMtronics blocking diodes
ii. MEMtronics switches for active solar cell array reconfiguration.
iii. Micro thermoelectric generators
2.5 Propulsion systems
i. Micromachined pressure sensors
ii. Micromachined chemical sensors (leak detection)
iii. Arrays of single shot thrusters (digital propulsion)
iv. Continuous microthrusters (cold gas, combustible solid resist jet)
v. Pulsed microthrusters
2.6 Thermal control systems
i. Micro heat pipes
ii. Micro radiators

iii. Thermal switches
2.7 Communication and radar systems
i. Very high band width, low power, low resistance radio
ii. frequency (RF) switches
iii. Micromirrors and micro-optics for laser communications
iv. Micromechanical variable capacitors, inductors and oscillators
2.8 Space environment sensors
i. Micromachined magnetometers
ii. Gravity-gradient monitors (nano-g accelerometers)
2.9 Distributed semiautonomous sensors
i. Multiparameter sensor ASIM with accelerometers
ii. chemical sensors
2.10 Interconnects and packaging
iii. Interconnects and packaging designed for ease of reparability
iv. Field programmable interconnect structures
v. “Smart” interconnects for positive-feedback
Inserting micro engineering technology into current systems can provide better monitoring of system
status and health, which can help resolve potential operational abnormalities and permit increased
functionality with almost negligible weight or power impacts.MEMS and ASIM technologies can
also be used to instrument the launch vehicle. Current launch vehicles such as TITAN IV are often
instrumented to measure the lift-off and ascent flight environments. MEMS sensors (accelerometers,
chemical sensors etc.) coupled to data transceivers can be used in a wireless network system onboard
the vehicle and on the launch site.

CHAPTER 3
MICRO FABRICATION TECHNIQUES
Micro fabrication techniques for making mechanical parts. Motors, pivots, linkages, and other
mechanical devices can be made to fit inside this circle “O”. These devices are also potentially quite
inexpensive. For example, using silicon surface micromachining, a gear captivated on a pivot can be
made for less than a cent.
These technologies make devices ranging in size from a dozen millimeters to a dozen microns.
Silicon surface micromachining inexpensively makes completely assembled mechanical systems.
Silicon bulk micromachining uses either etches that stop on the crystallographic planes of a silicon
wafer or etches that act isotropic ally to generate mechanical parts. These techniques combined with
wafer bonding and boron diffusion allows complex mechanical devices to be fabricated.
The LIGA technology makes miniature parts with spectacular accuracy. Electro Discharge
Machining, EDM, extends conventional machine shop technology to make sub-millimeter sized
parts. .
Micromechanical parts tend to be rugged, respond rapidly, use little power, occupy a small volume,
and are often much less expensive than conventional macro parts. Belle Mead Research, BMR,
specializes in helping companies understand when it is advantageous to use micromechanical parts,
and developing products incorporating these devices.
3.1 Silicon surface micromachining
Silicon surface micromachining uses the same equipment and processes as the electronics
semiconductor industry. This has led to a very rapid evolution of silicon surface micromachining.
Very sophisticated equipment and experienced operators are available to manufacture these devices.
One company is even offering the integration of surface micro machined devices and CMOS
electronics on the same chip.
This technique deposits layers of sacrificial and structural material on the surface of a silicon wafer.
As each layer is deposited it is patterned, leaving material only where the designer wishes. When the
sacrificial material is removed, completely formed and assembled mechanical devices are left.
Figure 1 shows the process steps to make a gear. The oxide is the sacrificial material, and the
polysilicon is structural. one of the original set of gears W Trimmer and collaborators made at Bell
Laboratories.

Figure 1 The process make a gear
Comb drives actuators and electrostatic motors can be fabricated using this technique. The curved
white fingers are fixed to the substrate, and the gray fingers are free to move. By applying a voltage
alternately to the top and bottom white fingers, the electrostatic force causes the gray structure to
start to resonate. Depending upon the frequency of excitation, the mass can be made to translate, or
rotate.

CHAPTER 4
MEMS DEVICES
4.1 Micro heat pipe
Within the spacecraft, heat pipes are normally used to provide high thermal conductivity paths.
Miniature heat pipes have diameters on the order of 1mm: while micro heat pipes have diameters on
the order of 10micro.m.Heat pipe is a sealed vessel as a thermal conductance device. Working fluid
is charged in heat pipe. The phase of working fluid at evaporator section (heat source) is changed
from liquid to vapor and contrarily changed at condenser section and cooled.
Figure 2 Micro heat pipe
Cooled working fluid is returned to from condenser to evaporator by capillary action within wick
structure. It dissipates energy from heat source by the latent heat of evaporation in a nearly
isothermal operation. Working fluid is circulated inside heat pipe accompanying with the phase
change at both evaporator and condenser. So, also called two-phase convection device. The basic
elements of heat pipe are shown figure. A number of heat pipes have been developed to cool
numerous applications, such as microelectronics chip, space, reactor, engine, etc.The fabrication is

relatively straightforward using a (100) silicon wafer. A long thin exposed region of silicon can be
anisotropically etched to produce a "V" groove, which becomes a sealed tube when bonded against a
flat surface. Methanol has been used as the working fluid. The results show an increase in effective
thermal conductivity of up to 81%, compared with a standard silicon wafer, and a significantly
improved transient thermal response. Micro machined heat pumps may provide an effective way of
removing heat from the integrated circuits without using metallic radiator elements.
4.2 Silicon satellites
Silicon satellites (also known as nanosatellites) were introduced by Janson, Helvajian and Robinson.
This concept presents a new paradigm for space system design, construction, testing, architecture and
deployment. Integrated spacecraft that are capable of attitude and orbit control for complex space
missions can be designed for mass production using adaptations of semiconductor batch fabrication
techniques. Useful silicon satellites have dimensions of 10 to 30cms; while more complex
configurations using additional non silicon mechanical structure (i.e. truss beams, honeycomb panels
and inflatable structures) will be much larger. The benefits of silicon satellites are as follows.
• Radically increased functionality per unit mass
• Ability to produce 10,000 or more units for “throw away” and dispersed satellite missions.
• Decreased material variability and increased reliability because of rigid process control.
• Rapid prototyping production capability using electronic circuit, sensor and MEMS design
libraries with existing computer aided design (CAD/CAM)
• Reduced number of piece parts
• Ability to tailor design in CAD/CAM to fabricate mission specific units.
Silicon satellites are classified as follows
• Micro satellites (1kg 100kg mass)
• Nano satellites ( 1g – 1kg mass)
• Pico satellites ( 1mg – 1g)
• Femi satellites (1 micro’s – 1mg mass)
These technologies permit the integration of the C&DH and communication systems, low resolution
attitude sensors, inertial navigation sensors and a propulsion system into a 1cm cube or smaller size
satellite. Pico satellites and Femi satellites would be ideal as simple environment sensors. Using only
solar radiation and depending on the overall configuration, Pico satellites through micro satellites can
produce power levels in the 1 – 100w range. Pico satellites are the smallest useful satellites, but

active thermal control will be required. A thermally passive Pico satellite will have temperature
range swings of 90k between sunlight and eclipse on low earth orbit. Cubic Pico satellites made of
silicon can have as much as 0.18cm radiation shielding and orbit lifetimes of several years at 700km
altitude under solar maximum conditions. These silicon satellites can be good for disposable or short
duration missions.

CHATER 5
SOLAR SAIL
Hundreds of space missions have been launched since the last lunar mission, including several deep
space probes that have been sent to the edges of our solar system. However, our journeys to space
have been limited by the power of chemical rocket engines and the amount of rocket fuel that a
spacecraft can carry. Today, the weight of a space shuttle at launch is approximately 95 percent fuel.
What could we accomplish if we could reduce our need for so much fuel and the tanks that hold it?
International space agencies and some private corporations have proposed many methods of
transportation that would allow us to go farther, but a manned space mission has yet to go beyond the
moon. The most realistic of these space transportation options calls for the elimination of both rocket
fuel and rocket engines -- replacing them with sails.
NASA is one of the organizations that have been studying this amazing technology called solar
sails that will use the sun's power to send us into deep space. 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. Light sails could also be
driven by energy beams to extend their range of operations, which is strictly beamed sailing rather
than solar sailing. 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 interplanetary space or in orbit around a planet or small body. A typical
spacecraft going to Mars, for example, will be displaced by thousands of kilometers by solar
pressure, so the effects must be accounted for in trajectory planning, which has been done since the
time of the earliest interplanetary spacecraft of the 1960s. Solar pressure also affects the attitude of a
craft, a factor that must be included in spacecraft design.
The total force exerted on a solar sail may be around 1 newton (0.22 lbf) or less, making it a low-
thrust propulsion system, similar to spacecraft propelled by electric engines.
5.1 History concept

Nearly 400 years ago, as much of Europe was still involved in naval exploration of the
world, Johannes Kepler proposed the idea of exploring the galaxy using sails. Through his
observation that comet tails were blown around by some kind of solar breeze, he believed sails could
capture that wind to propel spacecraft the way winds moved ships on the oceans. While Kepler's idea
of a solar wind has been disproven, scientists have since discovered that sunlight does exert enough
force to move objects.
There are following statements for solar sail development :-
1. Johannes Kepler observed that comet tails point away from the Sun and suggested that the
sun caused the effect. In a letter to Galileo in 1610, he wrote, "Provide ships or sails adapted
to the heavenly breezes, and there will be some who will brave even that void." 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.
2. James Clerk Maxwell, in 1861–64, published his theory of electromagnetic fields and
radiation, which shows that light has momentum and thus can exert pressure on
objects. Maxwell's equations provide the theoretical foundation for sailing with light
pressure. So by 1864, the physics community and beyond knew sunlight carried momentum
that would exert a pressure on objects.
3. Jules Verne, in From the Earth to the Moon, published in 1865, wrote "there will some day
appear velocities far greater than these [of the planets and the projectile], of which light or
electricity will probably be the mechanical agent ... we shall one day travel to the moon, the
planets, and the stars." This 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 light pressure, although he did not develop the concept further. Verne
probably got the idea directly and immediately from Maxwell's 1864 theory (although it
cannot be ruled out that Maxwell or an intermediary recognized the sailing potential and
became the source for Verne).
4. Pyotr Lebedev was first to successfully demonstrate light pressure, which he did in 1899 with
a torsional balance; Ernest Nichols and Gordon Hull conducted a similar independent
experiment in 1901 using a Nichols radiometer.
5. Albert Einstein provided a different formalism by his recognizing the equivalence of mass
and energy. We can now write simply p = E/c as the relationship
between momentum, energy, and speed of light.

6. Svante Arrhenius predicted in 1908 the possibility of solar radiation pressure distributing life
spores across interstellar distances, the concept of panspermia. He apparently was the first
scientist to state that light could move objects between stars.
7. Friedrich Zander (Tsander) published a technical paper that included technical analysis of
solar sailing. Zander wrote of "using tremendous mirrors of very thin sheets" and "using the
pressure of sunlight to attain cosmic velocities".
8. J.D. Bernal wrote in 1929, "A form of space sailing might be developed which used the
repulsive effect of the sun's rays instead of wind. A space vessel spreading its large, metallic
wings, acres in extent, to the full, might be blown to the limit of Neptune's orbit. Then, to
increase its speed, it would tack, close-hauled, down the gravitational field, spreading full sail
again as it rushed past the sun."
The first formal technology and design effort for a solar sail began in 1976 at Jet Propulsion
Laboratory for a proposed mission to rendezvous with Halley's Comet. To take advantage of this
force, NASA has been experimenting with giant solar sails that could be pushed through the cosmos
by light.
There are three components to a solar sail-powered spacecraft:
• Continuous force exerted by sunlight
• A large, ultrathin mirror
• A separate launch vehicle
A solar sail-powered spacecraft does not need traditional propellant for power, because its propellant
is sunlight and the sun is its engine. Light is composed of electromagnetic radiation that exerts force
on objects it comes in contact with. NASA researchers have found that at 1 astronomical unit (AU),
which is the distance from the sun to Earth, equal to 93 million miles (150 million km), sunlight can
produce about 1.4 kilowatts (kw) of power. If you take 1.4 kW and divide it by the speed of light,
you would find that the force exerted by the sun is about 9 newtons (N)/square mile (i.e., 2
lb/km2
or .78 lb/mi2
). In comparison, a space shuttle main engine can produce 1.67 million N of force
during liftoff and 2.1 million N of thrust in a vacuum. Eventually, however, the continuous force of
the sunlight on a solar sail could propel a spacecraft to speeds five times faster than traditional
rockets.
5.2 Principle of Solar sail
5.2.1 Solar radiation pressure
Solar radiation exerts a pressure on the sail due to reflection and a small fraction that is absorbed.
The absorbed energy heats the sail, which re-radiates that energy from the front and rear surfaces.

The momentum of a photon or an entire flux is given by p = E/c, where E 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 1361 W/m2
at 1 AU (earth-sun distance), as revised in 2011.
perfect absorbance: F = 4.54 μN per square metre (4.54 μPa)
perfect reflectance: F = 9.08 μN per square metre (9.08 μPa) (normal to surface)
A perfect sail is flat and has 100% specular reflection. An actual sail will have an overall efficiency
of about 90%, about 8.25 μN/m2
, due to curvature (billow), wrinkles, absorbance, re-radiation from
front and back, non-specular effects, and other factors.
Figure 3 Solar radiation pressure
The 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
F = F0 cos2
θ / R2
(ideal sail)

where R is distance from the sun in AU. An actual square sail can be modeled as:
F = F0 (0.349 + 0.662 cos 2θ − 0.011 cos 4θ) / R2
Note that the force and acceleration approach zero generally around θ = 60° rather than 90° as one
might expect with an ideal sail.
Solar wind, the flux of charged particles blown out from the sun, exerts a nominal dynamic pressure
of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail.
Figure 4 Working concept of solar sail
5.2.2 Sail parameters
Sail loading (areal density) is an important parameter, which is the total mass divided by the sail
area, expressed in g/m2
. It is represented by the Greek letter σ. A sail craft has a characteristic
acceleration, ac, which it would experience at 1 AU when facing the sun. It is related to areal density
by:
ac = 8.25 / σ, in mm/s2
(assuming 90% efficiency)

The lightness number, λ, is the dimensionless ratio of maximum vehicle acceleration divided by the
sun's local gravity; using the values at 1 AU:
λ = ac / 5.93
The table presents some example values. Payloads are not included. The first two are from the
detailed design effort at JPL in the 1970s. The third, the lattice sailer, might represent about the best
possible performance level. The dimensions for square and lattice sails are edges. The dimension for
heliogyro is blade tip to blade tip.
Type σ ac λ Size
Square sail 5.27 1.56 0.26 820 m
Heliogyro 6.39 1.29 0.22 15 km
Lattice sailer 0.07 117 20 1 km
5.2.3 Attitude control
An active attitude control system (ACS) is essential for a sail craft to achieve and maintain a desired
orientation. The required sail orientation changes slowly, often less than 1 degree per day, in
interplanetary space, but much more rapidly in a planetary orbit. The ACS must be capable of
meeting these orientation requirements. Control is achieved by a relative shift between the
craft's center of pressure and its center of mass. This can be achieved with control vanes, movement
of individual sails, movement of a control mass, or altering reflectivity. Holding a constant attitude
requires that the ACS maintain a net torque of zero on the craft. The total force and torque on a sail,
or set of sails, is not constant along a trajectory. The force changes with solar distance and sail angle,
which changes the billow in the sail and deflects some elements of the supporting structure, resulting
in changes in the sail force and torque. Sail temperature also changes with solar distance and sail
angle, which changes sail dimensions. The radiant heat from the sail changes the temperature of the
supporting structure. Both factors affect total force and torque. The ACS must compensate for all of
these changes for it to hold the desired attitude.

5.2.4 Constraints
In Earth orbit, solar pressure and drag pressure are typically equal at an altitude of about 800 km,
which means that a sail craft would have to operate above that altitude. Sail craft must operate in
orbits where their turn rates are compatible with the orbits, which is generally a concern only for
spinning disk configurations.
Sail operating temperatures are a function of solar distance, sail angle, reflectivity, and front and
back emissivities. A sail can be used only where its temperature is kept within its material limits.
Generally, a sail can be used rather close to the sun, around 0.25 AU, or even closer if carefully
designed for those conditions.
5.3 Solar sail construction
The strategy for near-term sail construction is to make and assemble as much of the sail as
possible on earth. Thus, while the delicate films of the sail must be made in space, all other
components are made on earth. The sail construction system consists of the following elements: a
scaffolding (to control the structure's deployment), the film fabrication device, a panel assembly
device, and a "crane" for conveying panels to the installation sites.
The scaffolding structure rotates at a rate within the operational envelope of the sail itself, to
facilitate the sail's release. Six compression members define the vertical edges of the hexagonal
prism. Many tension members parallel to the base link these compression members to support them
against centrifugal loads. Ballast masses flung further from the axis provide additional radial tension
and rigidity near the top of the scaffolding. Other tension members triangulate the structure for
added rigidity. Tension members span the base of the prism, supporting a node at its center. The
interior is left open, providing a volume for deploying and assembling the sail. The top space is left
open, providing an opening for removing it. The face of the sail is near the top of the scaffolding,
and the rigging below. If the scaffolding is oriented properly, the sun will shine on the usual side of
the sail, making it pull up on its attachment point at the base of the prism. The total thrust of the said
is then an upper bound on the axial load supported by the compression members. It is clearly
desirable to make the scaffolding a deployable structure.
The sail's structure consists of a regular grid of tension members, springs, and dampers, and a less
regular three-dimensional network of rigging. This is a very complex object to assemble in space.
Fortunately, even the structure for a sail much larger than described herein can be deposited in the
Shuttle payload bay in deployable form.

Since the sail is a pure tension structure, its structural elements can be wound up on reels.
Conceptually, the grid structure can be shrunk into a regular array of reels and a plane. With each
node in the lid represented by housings containing three reels. The rigging can be sunken into a less
regular array, and the nodes containing its reels stacked on top of those of the grid.
The structure will be deployed by pulling on cords attached to certain nodes. Deployment may be
controlled by a friction brake in the hubs of the reels. By setting the brakes properly, positive
tension must be applied for deployment and certain members may be made to deploy before others.
Further control of the deployment sequence, if needed, may be introduced by a mechanism which
prevents some elements from beginning to deploy until selected adjacent elements have finished
deploying. If detailed external intervention is deemed desirable, brakes could be rigged to release
when a wire on the housing is severed by laser pulse.
The film fabrication device produces a steady stream of film triangles mounted to foil spring
clusters at their corners. The panel fabrication device takes segments of the stream and conveys
them along a track to assembly stations. Each segment is fastened to the previous segment and to
the edge tension members that will frame the finished panel. This non-steady process of panel
assembly requires a length of track to serve as a buffer with a steady film production process.
At the assembly station, the segments are transferred to fixtures with a lateral transport capability.
During transfer, each segment is bonded to the one before along one edge. While the next segment
is brought into position, the last segment is indexed over a one strip width, completing the cycle.
Special devices bearing the edge tension members travel on tracts and place foil tabs on the panel
structure. The foil tabs linking the segments may be bonded to one another in many ways, including
ultrasonic welding, spot welding, and stapling. Attachment and conveyance may be integrated if the
foil tabs are hooked over pins for conveyance. The panel assembly cycle ends with a pause, as the
completed panels, now held only by their corners, are lured into a storage region and new edge
members are loaded into position.
At this point the sail's structure is deployed within scaffolding, and panels are being produced and
stored at a panel fabrication module. The stored panels are initially loaded at a node suspended on
tension members above the center of the sail. A crane is likewise suspended, but from tension
members terminated in actively controlled reels mounted on devices free to move around the top of

the scaffolding. This makes it possible to position the crane over any aperture in the grid.
Once panel installation is complete and the operation of various reels has been checked, the sail is
ready for release and use. It is already spinning at a rate within its operational envelope, and is
already under thrust; hence, this task is not difficult. First, the sail's path must be cleared. To do this,
the film fabrication device, its power supply, the panel assembly device, and the crane are conveyed
to the sides of the scaffolding in a balanced fashion. The top face is cleared of objects and tension
members. Then, the members holding the corners of the sail are released, and the remaining
restraint points are brought forward to carry the sail out of the scaffolding. Finally, all restraints are
released, and the sail rises free.
Figure 5 A four quadrant, 20-meter solar sail system is fully deployed during
testing at NASA Glenn Research Center's Plum Brook facility in Sandusky,
Ohio.

CHAPTER 6
SOLAR SAIL DYNAMICS AND CONTROL
There are essentially two modes for operation and control of the solar sail.
In the first mode, the tilting of panels produces control forces. Each panel has a mass of some 0.3 to
1.1 kilograms. This first mode is conceived of as a semi-passive control mode for interplanetary
cruising (where only slow changes of attitude are needed). It is of importance to consider the stability
of a passive sail set at various angles to the sun. In the ideal sail approximation (planar, perfectly
reflecting), thrust will be normal to the sail and act through its center of area, that is, along the axis of
symmetry. In an absorbing sail, its thrust is divided into purely reflective and purely absorptive
components. The former produces no torque, while the latter produces a torque. To counter this
torque, light pressure must be increased on the far side of the sail from the sun relative to that on the
near side. Making the sail concave toward the payload accomplishes this purpose.
Since torques can be balanced at all sail angles of interest, small perturbing torques can shift the sail
from one attitude to another, or change its rotation rate. Since heliocentric orbit times are typically
months, spin-up and spin-down times of ten days and precession rates of 0.1 radian/day seem
reasonable targets. Tilting a panel by about twenty degrees changes the force on it--both normal to
the sail and parallel to it--by about thirty percent of the panel's maximum thrust. Sail operation in this
first mode configuration is characterized by torques that may be ballasted by a few statically
positioned trim panels 100, permitting an entirely passive cruise mode. Slow changes in the sail's
attitude and spin rate may be made, from time to time, by cyclic variation of panel tilt to produce
perturbing torques. The passivity of cruise mode and the ease of providing redundant tiltable panels
recommend this mode for reliable interplanetary transportation.
In the second mode of sail configuration, the payload mass is assumed to be large compared to the
sail mass, and the sail is considered as a separate object linked to it by actively controlled shroud
lines 202 and 204. In the second mode, the tilting of the panels 200 controls the spin rate. However,

in this mode precession is effected by varying the tension exerted by the shrouds 202 and 204 on
different parts of the sail. This is accomplished by reeling and unreeling the shrouds in a coordinated
fashion as the sail turns. For the sail discussed above, and the probable range of sail performances,
this arrangement implies precession rates of 13 to 26 rad/100 minutes, when the sail is flat with
respect to the sun. This provides a generous margin in turn rate, even from maneuvers in low earth
orbits. This active control permits damping of nutation. This is important, since nutation would
otherwise be initiated by rapid changes in precession rate. It should be noted that during precession
the payload is offset from the axis of rotation in a direction fixed in inertial space.
For missions involving both interplanetary cruise and circumplanetary maneuvering, a vehicle able to
operate in both modes is desirable. The first mode has a decisive advantage near planets (because of
its maneuverability), but cannot enter a passive cruise mode. The greater distance between the
payload and sail in this mode precludes balancing the torque on the sail resulting from absorbed light
with a reasonable amount of concavity, as is done in the first mode. Instead, the torque must be
countered in the same manner as the sail is processed: by active manipulation of shroud tension.
While control of shroud tension might be made redundant by placing reels at both ends of the lines,
reliability still favors a passive system on long missions. Fortunately, interconversion seems simple.
The second mode control can be maintained as the shroud lines 202 and 204 are reeled in, so long as
the sail is properly ballasted for mode one. While the payload reaches the mode one position, the reel
can be locked and mode one control begun.
6.1 Cruising by sunlight
Maneuvering a solar-sail spacecraft requires balancing two factors: the direction of the solar sail
relative to the sun and the orbital speed of the spacecraft. By changing the angle of the sail with
respect to the sun, you change the direction of the force exerted by sunlight.
When the spacecraft is in orbit around the Earth or sun, it is traveling in a circular or elliptical path at
a given speed and distance. To go to a higher orbit (travel farther away from the object), you angle
the solar sail with respect to the sun so that the pressure generated by sunlight is in the direction of
your orbital motion. The force accelerates the spacecraft, increases the speed of its orbit and the
spacecraft moves into a higher orbit. In contrast, if you want to go to a lower orbit (closer to the
object), you angle the sail with respect to the sun so that the pressure generated by the sunlight is
opposite the direction of your orbital motion. The force then decelerates the spacecraft, decreases the
speed of its orbit and the spacecraft drops into a lower orbit.

The pressure of sunlight decreases with the square of the distance from the sun. Therefore, sunlight
exerts greater pressure closer to the sun than farther away. Future solar-sail spacecraft may take
advantage of this fact by first dropping to an orbit close to the sun -- a solar fly-by -- and using the
greater sunlight pressure to get a bigger boost of acceleration at the start of the mission. This is called
a powered perihelion maneuver.
CHAPTER 7
SOLAR SAIL MATERIALS
While solar sails have been designed before (NASA's had a solar sail program back in the 1970s),
materials available until the last decade or so were much too heavy to design a practical solar sailing
vehicle. Besides being lightweight, the material must be highly reflective and able to tolerate extreme
temperatures. The giant sails being tested by NASA today are made of very lightweight, reflective
material that is upwards of 100 times thinner than an average sheet of stationery. This "aluminized,
temperature-resistant material" is called CP-1. Another organization that is developing solar sail
technology, the Planetary Society (a private, non-profit group based in Pasadena, California),
supports the Cosmos 1, which boasts solar sails that are made of aluminum-reinforced Mylar and are
approximately one fourth the thickness of a one-ply plastic trash bag.
Figure 6 Aluminium being manufactured for the Solar Sail

The reflective nature of the sails is the key. As photons (light particles) bounce off the reflective
material, they gently push the sail along by transferring momentum to the sail. Because 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. Although 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.
7.1 Aluminum as solar sail material
The thin metal film, according to the preferred embodiment of this invention, is an aluminum film.
Aluminum films have high reflectivity, low density, a reasonable melting point, and a very low vapor
pressure. The reflectivity and transmissivity of aluminum film is a function of its thickness.
Generally, reflectivity for short wave lengths falls off faster with decreasing film thickness than for
longer wave lengths. Consequently, any aluminum film thick enough to reflect well in the visible
wave lengths should reflect even better in the infrared, where roughly half the sun's power output
lies. Even in the visible wave length, aluminum's reflectivity remains near its bulk value down to a
thickness of 30 nm, and remains above 0.8down to about 15 nm. The reflectivity of aluminum films
varies with the deposition conditions. Over a range of at least 300 degrees to 473 degrees Kelvin,
reflectivity increases with decreasing substrate temperatures. High deposition rates, near-normal
vapor incidence, and a good vacuum favor high reflectivity. In general, poor deposition conditions
reduce reflectivity with a shorter wave length more than for a longer wave length, and thicker films
are more sensitive to vapor incidence angle than are thin films. Since most of the sun's power output
is at comparatively long wave lengths, and since the films are to be quite thin, poor deposition
conditions should not greatly affect sail performance.
Above some temperature, thin metal films fail by agglomeration. This occurs because thin films have
an enormous ratio of surface to volume, permitting them to substantially reduce the surface energy
by forming droplets. Above the melting point, the material rearranges swiftly, like a soap bubble
bursting. At temperatures somewhat below the melting point, agglomeration into droplets occurs far
more slowly, through surface diffusion. Thin films made from silver, with a melting point of
1235degrees Kelvin agglomerate at less than 500 degrees Kelvin. However, the analogous
temperature for aluminum is a mere 378 degrees Kelvin. Nevertheless, aluminum films have
survived fifteen minute anneals at 673 degrees Kelvin, and two hour anneals at700 degrees Kelvin.
The reason for this discrepancy is the presence of an oxide layer on the aluminum, which armors the
surface with a rigid, refractory skin, thereby inhibiting surface diffusion and preventing changes of

shape.
Since the film is to be hot and mounted under tension, creep is of concern. The interior of a small
droplet will be in compression, because of its surface energy and resulting force of surface tension.
In like fashion, the interior of a thin film will be in compression, unless the mounting tension exceeds
its surface tension. Considering the oxide-coated film, elongation not only breaks the oxide skin
(which may be very strong), but also creates a fresh, uncoated aluminum surface. To shrink, on the
other hand, it must somehow crush or destroy the outside surface, which it clearly cannot do. In fact,
shrinkage would manifest itself as agglomeration, as discussed above.
The strength of a variety of thin metal films and thicker vapor deposited sheets has been measured
experimentally. Metals in thin films have mechanical properties differing from those of the bulk
material, because of the close proximity of all parts of the film to the surface. The yield and fracture
stresses of aluminum film increase as the film gets thinner. Aluminum films show substantial
ductility, and a variable degree of deformation before failure.
Aluminum films of the minimum thickness required for reflectivity may prove too weak to support
the stresses imposed upon them during fabrication and operation, or may creep under load at elevated
temperatures. If so, it is possible to strengthen them, not by adding further aluminum, but by adding a
reinforcing film of a stronger, more refractory material. A good reinforcing film should be strong,
light, and easy to deposit. It need not be chemically compatible with aluminum, since a few
nanometers of some other material can serve as a barrier to diffusion. A reinforcing film is apt to
have a high modulus such that it will act as the sole load bearing element in the composite film. The
aluminum film could help contribute tear resistance, however. The use of a metal as a reinforcing
film could reduce the amount of aluminum needed to give good reflectance. Some metals, such as
nickel, may reflect well enough to be of interest by themselves.
7.2 Titanium as reinforcing material
Films of pure titanium from 150 to 2,000 nanometers thick were found to have strengths of 460 to
620 NPa, while vapor deposited foils of Pi-6Al-4V from 40,000 to 2,000,000 nanometers thick had
tensile strengths of 970 to 1200 NPa. Titanium has enough strength and temperature tolerance to
make it an attractive choice as a reinforcing film.

7.3 Nickel as reinforcing material
The strength of nickel film exceeds 2,000 NPa at a thickness of 70 nanometers or less, dropping to
1500 NPa on annealing. Nickel’s density is a disadvantage for use in sails of the highest
performance, which should prove acceptable for bulk transport sails.
7.4 Silicon monoxide as reinforcing material
Silicon monoxide is a popular thin film material with many uses. On aluminum, these films have
found extensive use as satellite thermal control coatings, and have demonstrated their stability in the
space environment. Mounted on fine metal meshes, unbacked SiO films as thin as 2.5 nanometers
have found use as specimen supports in electron microscopy; such films are described as having
"great strength," and are so stable at high temperatures that they may be cleaned by passing them
rapidly through a flame. Since silicon monoxide is easy to evaporate, is refractory, has a low density,
is apparently of high strength in extremely thin film form, and is of known space compatibility,
silicon monoxide shows promise as a reinforcing film material.
7.5 Boron as reinforcing material
Vapor deposited boron film has a strength of 620 MPa. Since it is light and refractory, boron may
prove desirable as a reinforcing material. Carbon forms amorphous films of "exceptional strength;"
those used in electron microscopy are made as thin as 4 nanometers. Since carbon is strong, light,
refractory, and easy to deposit, it is a promising material for reinforcing film. For a wide variety of
reasons, the sail surface will not be one big piece of film, but rather many smaller sheets mounted on
a structure. Since the fabrication device, as described hereinafter, will produce strips, natural choices
for the shapes of the sheet include long strips, shorter rectangles or squares cut from strips, and
triangles cut from the strips. The sheets must be tensioned, and should be planar. Since a triangular
sheet will be planed if tensioned at its corners, and since triangular sheets will fit well into a fully
triangulated structure, they will be used as a basis for further design.
In 2000, Energy Science Laboratories developed a new carbon fiber material which might be useful
for solar sails. The material is over 200 times thicker than conventional solar sail designs, but it is so
porous that it has the same weight. 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.

Tears are a critical concern in the use of thin films for solar sails. While even sheets of extremely
thin material have adequate strength to support the load expected during fabrication and operation in
the absence of stress concentrations, the inevitability of manufacturing flaws and micrometeoroid
damage makes this a small comfort. A means of limiting the spread of tears would be desirable, as it
would allow a thinner sheet to tolerate greater damage without failure. The most obvious method of
limiting tears is to mount the film on a supporting mesh. However, differing coefficients of thermal
expansion and differing temperature between the mesh and the film are apt to make the film become
slack and lose its flatness, or become taut and possibly tear. Further, the mesh adds mass to the sail
and, because it must be fabricated, transported into space and attached to the film, adds cost as well.
A more natural approach to tear-stopping is to subdivide the film, convert it from a continuous sheet
to a redundant network of small, load-bearing elements. In such a structure, a large manufacturing
flow or a grazing micrometeoroid impact is free to initiate a tear--but the tear will cause the failure,
not of an entire sheet, but of a small piece of film, perhaps 25 square millimeters in area. Patterns of
cuts and wrinkles can de-tension areas of film to isolate stress to smaller regions. Each wrinkled
region is fabricated with enough extra material to avoid being stretched flat as the film is tensioned.
Stress isolation is aided by slits extending perpendicular to the boundary. The slits are terminated at
their stress bearing ends in a way that avoids initiation of tears. This approach to tear resistance
appears superior to that of mounting the films on a metal mesh. It involves the fabrication of no
additional elements and the addition of no extra mass. By taking advantage of the natural strength of
the films, it avoids slackness due to differential expansion and yields a flatter sail.

CHAPTER 8
DESIGNS FOR SOLAR SAIL LAUNCH
With just sunlight as power, a solar sail would never be launched directly from the ground. A second
spacecraft is needed to launch the solar sail, which would then be deployed in space. Another
possible way to launch a solar sail would be with microwave or laser beams provided by a satellite or
other spacecraft. These energy beams could be directed at the sail to launch it into space and provide
a secondary power source during its journey. In one experiment at NASA's Jet Propulsion
Laboratory (JPL), sails were driven to liftoff using microwave beams, while laser beams were used
to push the sail forward. Once launched, the sails are deployed using an inflatable boom system that
is triggered by a built-in deployment mechanism.
Figure 7 Processing of launching solar sail

8.1 Investigated sail designs
The highest thrust-to-mass designs known (2007) were theoretical designs developed by Eric
Drexler. He designed a sail using reflective panels of thin aluminum 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 accelerations an order of magnitude higher than designs based on deployable plastic
films.
Figure 8 View of solar sail in space
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 guide 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.
.
Figure 9 Structure of solar sail
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.
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 altitude and direction were to be
completely controlled by changing the angle of the blades in various ways, similar to the cycle 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.
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. Weights 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. 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.
8.2 COSMOS-1 spacecraft design
The first solar-sail spacecraft, called Cosmos-1, has been developed, built and tested by The
Planetary Society, a private, non-profit organization whose goal is to encourage the exploration of
our solar system. The Planetary Society contracted a Russian space organization, the Babakin Space
Center, to build, launch and operate the spacecraft. The cost of the project is about $4-million and is
funded by Cosmos Studios, a new science-based media company.
The spacecraft itself weighs 88 lb (40 kg) and can sit on a tabletop. After a first-phase test launch, the
spacecraft will be launched into Earth orbit -- 522 mi (840 km) perigee and 528 mi (850 km) apogee.

Figure 10 COSMOS-1 spacecraft in orbit
The spacecraft systems include:
1. Solar sail
i. made of aluminized Mylar
ii. thickness of 0.0002 inches (5 microns)
iii. area of 6,415 square feet (600 square meters)
iv. arranged in eight triangular blades:
v. each about 49 ft (15 m) long
vi. consist of inflatable plastic tubes that support the sail (a foam may be used
inside the tubes to hold them rigid once inflated)
vii. can be pivoted (like a helicopter blade) by electric motors to change its angle
relative to the sun
2. Solar-sail deployment A pressurized gas-filling system inflates the plastic tubes.

3. Power - A small array of solar cells supplies all of the electrical power.
4. Navigation - It is essential for the spacecraft to know where it is and where the sun is at all
times.
i. A sensor detects the position of the sun.
ii. A global positioning system (GPS) receiver detects the spacecraft's
position. (From the ground, the spacecraft orbit will be determined from
Doppler tracking data with the aid of on-board accelerometers, which
we'll discuss later.)
iii. The information from the sun sensor and the GPS receiver are
continuously relayed to the spacecraft's on-board computer.
iv. The on-board computer operate the motors that turn the sail blades to
maintain the proper orientation of the sail blades with respect to the sun.
v. The on-board computer can accept corrections or override commands
from the ground.
5. Communications - Redundant radio systems are used to communicate with flight
controllers on the ground.
• one UHF band, 400 megahertz
• one S-band, 2210 MHz
6. On-board computer
• Two 386EX series microprocessors
• old, but reliable in the harsh environment of outer space
• can be run in low-power modes, similar to laptop computers
• programmed to operate the on-board systems, relay information to the ground
and receive commands from the ground
• A software program assigns tasks to each microprocessor based on workload and
performance (speed, delay).
• Each processor has its own small amount of read-only memory (ROM) --
enough to boot the computer and load the operating system into random-access
memory (RAM).
• Three re-writable ROMs contain the operating systems and programs. The
copies of ROM are checked before use for errors caused by radiation in outer
space.

• Three RAMs are present to receive the operating system. Again, the integrity of
each RAM is checked for errors before loading.
• The ROM architecture allows programmers on the ground to update and re-boot
the spacecraft's software at any time. It also allows the spacecraft to function in
the case of severe radiation damage.
• Data are stored in two separate databases connected by serial and parallel
systems.
7. Instruments
• Two on-board imaging cameras (Russian and American) to document the
mission
• On-board accelerometers to measure the acceleration of the spacecraft due to
sunlight pressure (non-gravitational acceleration)
CHAPTER 9
OPERATIONS OF SOLAR SAIL
There are some operation of solar sail.,
9.1 Changing orbits
Sailing operations are simplest in interplanetary orbits, where attitude changes are done at low rates.
For outward bound trajectories, the sail force vector is oriented forward of the Sun line, which
increases orbital energy and angular momentum, resulting in the craft moving farther from the Sun.
For inward trajectories, the sail force vector is oriented behind the Sun line, which decreases orbital
energy and angular momentum, resulting in the craft moving in toward the Sun. It is worth noting

that only the Sun's gravity pulls the craft toward the Sun—there is no analog to a sailboat's tacking to
windward. To change orbital inclination, the force vector is turned out of the plane of the velocity
vector. In orbits around planets or other bodies, the sail is oriented so that its force vector has a
component along the velocity vector, either in the direction of motion for an outward spiral, or
against the direction of motion for an inward spiral. Trajectory optimizations can often require
intervals of reduced or zero thrust. This can be achieved by rolling the craft around the sun line with
the sail set at an appropriate angle to reduce or remove the thrust.
Figure 11 Orbit changing of solar sail
9.2 Swingbys
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 swingby 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 swingby can also be used to obtain favorable departure or arrival
directions relative to Earth. A planetary swingby 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.
9.3 Smart lines
A smart line could be a critical element of sailing operations. As with maritime ships, lines are
essential for a wide range of uses. One difference is that some lines may be very long and need to be
self-guiding. The lines could extend from and retract into the sail craft. A 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. The
maneuvering unit is like a small spacecraft, with many of the same sensors and control systems. It
could draw power from and communicate with the sail craft through the line. These operations could
be done autonomously. Lines 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.
9.4 Towing
Smart lines can enable towing operations by being able to attach to or release objects at the remote
end of the line. Attached objects might be pulled in to the body of the sailer or remain at the end of
the deployed line. Objects to be towed may have attachment points that allow multiple sail craft to
engage in the towing. Towing operations can include deflecting large bodies that pose a hazard to
Earth, bringing natural bodies to Earth or other sites for resource recovery, and transporting disabled
spacecraft or other structures.
To 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 10
APPLICATIONS OF SOLAR SAIL
Potential applications for sail craft range throughout the solar system, from near the sun to the comet
clouds beyond Neptune. The craft can make outbound voyages to deliver loads or to take up station
keeping at the destination. They can be used to haul cargo and possibly also used for human travel.

10.1 Voyages
For trips within the inner solar system, they can deliver loads and then return to Earth for subsequent
voyages, operating as an interplanetary shuttle. For Mars in particular, the craft could provide
economical means of routinely supplying operations on the planet.
Solar sail craft can approach the sun to deliver observation payloads or to take up station keeping
orbits. They can operate at 0.25 AU or closer. They can reach high orbital inclinations, including
polar.
Solar sails can travel to and from all of the inner planets. Trips to Mercury and Venus are for
rendezvous and orbit entry for the payload. Trips to Mars could be either for rendezvous or swing by
with release of the payload for aerodynamic braking.
10.2 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.
10.3 Trajectory corrections
The MESSENGER probe orbiting Mercury used light pressure on its solar panels to perform fine
trajectory corrections on the way to Mercury. By changing the angle of the solar panels relative to
the Sun, the amount of solar radiation pressure was varied to adjust the spacecraft trajectory more
delicately than possible with thrusters. Minor errors are greatly amplified by gravity

assist maneuvers, so using radiation pressure to make very small corrections saved large amounts of
propellant.
10.4 Interstellar flight
In the 1970s, 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 super lasers. As the starship neared its
destination, the outer portion of the sail would detach. The outer sail would then refocus and reflect
the lasers back onto a smaller, inner sail. This would provide braking thrust to stop the ship in the
destination star system.
Both methods pose monumental engineering challenges. The lasers would have to operate for years
continuously at gigawatts 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 be needed 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, 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. 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.
Similar solar sailing, such launch and capture were suggested for directed panspermia to expand life
in other solar systems. Velocities of 0.0005 c could be obtained by solar sails carrying 10 kg
payloads, using thin solar sail vehicles with effective areal densities of 0.1 g/m2
with thin sails of
0.1 µm thickness and sizes on the order of one square kilometer. Alternatively, swarms of 1 mm
capsules can be launched on solar sails with radii of 42 cm, each carrying 10,000 capsules of a
hundred million extremophile microorganism to seed life in diverse target environments.
10.5 Deorbiting artificial satellites
Small solar sails have been proposed to accelerate the deorbiting of small artificial satellites from
Earth orbits. Satellites in low Earth orbit can use a combination of solar pressure on the sail and
increased atmospheric drag to accelerate satellite reentry.
CHAPTER 11
PROJECTS OF SOLAR SAIL

11.1 Projects operating or completed
11.1.1 IKAROS 2010
The model of IKAROS at the 61st
International Astronautical Congress in 2010 Japan's
JAXA successfully tested IKAROS in 2010. The goal was to deploy and control the sail and for the
first time determining the minute orbit perturbations caused by light pressure. Orbit determination
was done by the nearby AKATSUKI probe from which IKAROS detached after both had been
brought into a transfer orbit to Venus. The total effect over the six month' flight was 100 m/s.
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. In July, the next phase for the demonstration of acceleration by
radiation began. On 9 July 2010, it was verified that IKAROS collected radiation from the Sun and
began photon acceleration by the orbit determination of IKAROS by range-and-range-rate (RARR)
that is newly calculated in addition to the data of the relativization accelerating speed of IKAROS
between IKAROS and the Earth that has been taken since before the Doppler effect was utilized. 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. 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. IKAROS spent six months traveling to Venus, and
then began a three-year journey to the far side of the Sun.
11.1.2 Attitude (orientation) 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.
11.1.3 Sail deployment tests
NASA has successfully tested deployment technologies on small scale sails in vacuum chambers. On
February 4, 1993, the Znamya 2, a 20-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 2.5, failed to deploy properly. In 1999, a full-scale

deployment of a solar sail was tested on the ground at DLR/ESA in Cologne. On August 9, 2004, the
Japanese ISAS successfully deployed two prototype solar sails from a sounding rocket. A clover-
shaped sail was deployed at 122 km altitude and a fan-shaped sail was deployed at 169 km altitude.
Both sails used 7.5-micrometer film. The experiment purely tested the deployment mechanisms, not
propulsion.

11.1.3 Solar sail propulsion attempts
A joint private project between Planetary Society, Cosmos Studios and Russian Academy of
Science made two sail testing attempts: in 2001 a suborbital prototype test failed because of
rocket failure; and in June 21, 2005,Cosmos 1 launched from a submarine in the Barents Sea,
but the Volna rocket failed, and the spacecraft failed to reach orbit. They intended to use the
sail to gradually raise the spacecraft to a higher Earth orbit over a mission duration of one
month. On Carl Sagan's 75th birthday (November 9, 2009) the same group announced
plans 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 as of 2011 was waiting for a
piggyback launch opportunity. 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.
11.1.4 NanoSail-D 2010
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. The second backup
version, NanoSail-D2, also sometimes called simply NanoSail-D, 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. 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.
11.2 Projects in development or proposed
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. Manned space flight utilizing solar sails is still in the development
state of infancy.
11.2.1 Sunjammer 2015
A technology demonstration sail craft, dubbed Sunjammer, is in development with the intent to prove
the viability and value of sailing technology. Sunjammer has a square sail, 124 feet (38 meters) wide
on each side (total area 13,000 sq ft or 1,208 sq m). It will travel from the Sun-Earth L1 Lagrangian
point 900,000 miles from Earth (1.5 million km) to a distance of 1,864,114 miles (3 million
kilometers). The demonstration will launch on a Falcon 9 in 2015. It will be a secondary payload,
released after the placement of the DSCOVR climate satellite at the L1 point.
11.2.2 LightSail-1
The Planetary Society's solar sail project. A ground-based deployment test was successfully done at
Stellar Exploration in San Luis Obispo, California on March 4, 2011, with hardware and
software adjustments leading to further tests. The configuration has four sail panels supported
by four diagonal booms.
11.2.3 Gossamer deorbit sail
As of December 2013, the European Space Agency (ESA) has a proposed deorbit sail, named
"Gossamer", that would be intended to be used to accelerate the deorbiting of small (less than 700
kilograms (1,500 lb)) artificial satellites from low-Earth orbits. The launch mass is 2 kilograms
(4.4 lb) with a launch volume of only 15×15×25 centimetres (0.49×0.49×0.82 ft). Once deployed, the
sail would expand to 5 by 5 metres (16 ft × 16 ft) and would use a combination of solar pressure on
the sail and increased atmospheric drag to accelerate satellite reentry.
CHAPTER 12
ADVANTAGES AND LIMITATIONS OF SOLAR SAIL
12.1 Advantages
A solar sail is a spacecraft without a rocket engine. It is pushed along directly by light particles from
the Sun, reflecting off its giant sails. Because it carries no fuel and keeps accelerating over almost
unlimited distances, it is the only technology now in existence that can one day take us to the stars.

The major advantage of a solar-sail spacecraft is its ability to travel between the planets and to the
stars without carrying fuel. Solar-sail spacecraft need only a conventional launch vehicle to get into
Earth orbit, where the solar sails can be deployed and the spacecraft sent on its way. These spacecraft
accelerate gradually, unlike conventional chemical rockets, which offer extremely quick acceleration.
So for a fast trip to Mars, a solar-sail spacecraft offers no advantage over a conventional chemical
rocket. However, if you need to carry a large payload to Mars and you're not in a hurry, a solar-sail
spacecraft is ideal. As for traveling the greater distances necessary to reach the stars, solar-sail
spacecraft, which have gradual but constant acceleration, can achieve greater velocities than
conventional chemical rockets and so can span the distance in less time. Ultimately, solar-sail
technology will make interstellar flights and shuttling between planets less expensive and therefore
more practical than conventional chemical rockets. Solar sails will set new speed records for
spacecraft and will enable us to travel beyond our solar system.
12.2 Limitations
Solar sails don't work well, if at all, in low Earth orbit below about 800 km altitude due to erosion or
air drag. 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. Solar sails must face the sun to decelerate. Therefore, on trips
away from the sun, they must arrange to loop behind the outer planet, and decelerate into the
sunlight.
There is a common misunderstanding that solar sails cannot go towards their light source. This is
false. In particular, sails can go toward the sun by thrusting against their orbital motion. This reduces
the energy of their orbit, spiraling the sail toward the sun.
CHAPTER 13
MISUNDERSTANDING OF SOLAR SAIL
Critics of the solar sail argue that solar sails are impractical for orbital and interplanetary missions
because they move on an indirect course. However, when in Earth orbit, the majority of mass on
most interplanetary missions is taken up by fuel. A robotic solar sail could therefore multiply an
interplanetary payload by several times by reducing this significant fuel mass, and create a reusable,

multimission spacecraft. Most near-term planetary missions involve robotic exploration craft, in
which the directness of the course is unimportant compared to the fuel mass savings and fast transit
times of a solar sail. For example, most existing missions use multiple gravitational slingshots to
reduce necessary fuel mass, in order to save transit time at the cost of directness of the route.
There is also a misunderstanding that solar sails capture energy primarily from the solar wind high
speed charged particles emitted from the sun. These particles would impart a small amount of
momentum upon striking the sail, but this effect would be small compared to the force due to
radiation pressure from light reflected from the sail. The force due to light pressure is about 5,000
times as strong as that due to solar wind. A much larger type of sail called a magsail would employ
the solar wind.
It has been proposed that momentum exchange from reflection of photons is an unproven effect that
may violate the thermodynamical Carnot rule. This criticism was raised by Thomas Gold of Cornell,
leading to a public debate in the spring of 2003. This criticism has been refuted by Benjamin
Diedrich, pointing out that the Carnot Rule does not apply to an open system. Further explanation of
lab results demonstrating is provided. James Oberg has also refuted Dr. Gold's analysis: "But ‘solar
sailing’ isn’t theoretical at all, and photon pressure has been successfully calculated for all large
spacecraft. Interplanetary missions would arrive thousands of kilometers off course if correct
equations had not been used. The effect for a genuine ‘solar sail’ will be even more spectacular."
One way to see the conservation of energy as not a problem is to note that when reflected by a solar
sail, a photon undergoes a Doppler shift; its wavelength increases (and energy decreases) by a factor
dependent on the velocity of the sail, transferring energy from the sun-photon system to the sail. This
change of energy can easily be verified to be exactly equal (and opposite) to the energy change of the
sail.
CHAPTER 14
FUTURE SPACE TRAVEL
Solar sail technology will eventually play a key role in long-distance NASA missions. NASA
believes that the exploration of space is similar to the tale of the "Tortoise and the Hare," with
rocket-propelled spacecraft being the hare. In this race, the rocket-propelled spacecraft will quickly
jump out, moving quickly toward its destination. On the other hand, a rocket less spacecraft powered

by a solar sail would begin its journey at a slow but steady pace, gradually picking up speed as the
sun continues to exert force upon it. Sooner or later, no matter how fast it goes, the rocket ship will
run out of power. In contrast, the solar sail craft has an endless supply of power from the sun.
Additionally, the solar sail could potentially return to Earth, whereas the rocket powered vehicle
would not have any propellant to bring it back.
If NASA were to launch an interstellar probe powered by solar sails, it would take only eight years
for it to catch the Voyager 1 spacecraft (the most distant spacecraft from Earth), which has been
traveling for more than 20 years. By adding a laser or magnetic beam transmitter, NASA said it
could push speeds to 18,600 mi/sec (30,000 km/sec), which is one-tenth the speed of light. At those
speeds, interstellar travel would be an almost certainty.
Solar sailing is a way of moving around in space by allowing sunlight to push a spacecraft. In
everyday experience, we do not feel any kind of force or pressure from sunlight. This is because
sunlight is so gentle that all the other things in our environment - gravity, wind, and the strength of
our own bodies - drown it out. However, in space, there is no air, and objects are freely falling
through space instead of constantly fighting gravity. In this environment, sunlight can dominate and
allow spacecraft to move at will, like sailing vessels on Earth's oceans.
As it continues to be pushed by sunlight, the solar sail-propelled vehicle will build up speeds that
rocket powered vehicles would never be able to achieve. Such a vehicle would eventually travel at
about 56 mi/sec (90 km/sec), which would be more than 200,000 mph (324,000 kph). That speed is
about 10 times faster than the space shuttle's orbital speed of 5 mi/sec (8 km/sec). To give you an
idea how fast that is, you could travel from New York to Los Angeles in less than a minute with a
solar sail vehicle traveling at top speed.
CHAPTER 15
CONCLUSION
Micro-electromechanical systems and Solar Sail have proved to be a part of the developing age
especially in the field of space and technology. It can be seen that the incorporation of the MEMS
devices will increase the autonomy in the operations and increase availability through the use of
condition based maintenance protocols. Perhaps the most profound result from this revolution will be

that MEMS and MEMS devices will become truly a mass producible commodity much like the
dynamic RAM chip used today. A solar sail is a spacecraft without a rocket engine. It is pushed
along directly by light particles from the Sun, reflecting off its giant sails.
CHAPTER 16
REFERENCES
1. Official website of European Space Agency (www.esa.int)
2. Official website of Japan Aerospace Exploration Agency (JAXA)
(www.Jaxa.jp/index_e.html)
3. Official website of Indian Institute of Technology (www.iitb.ac.in)

4. Micro engineering technology for space Systems by H. Helvajian
5. "NASA - NanoSail-D Home Page". Nasa.gov.
6. "LightSail-1- A Solar Sail Mission of The Planetary Society". Planetary.org.
7. "NASA Solar Sail Demonstration". www.nasa.gov
8. "IKAROS Project, JAXA Space Exploration Center". Jspec.jaxa.jp. 2010-05-21
9. "LightSail-1 on NASA Short List for Upcoming Launch". planetary.org. 2011-02-09
10. "Full-scale deployment test of the DLR/ESA Solar Sail". 1999.
11. "Cosmos 1 - Solar Sail (2004) Japanese Researchers Successfully Test Unfurling of Solar
Sail on Rocket Flight". 2004.
12. http://en.wikipedia.org/wiki/Solar_sail
13. http://en.wikipedia.org/wiki/Microelectromechanical_systems

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