Solar sails use radiation pressure from the sun for propulsion and have minimal moving parts. They produce very small thrusts but can be used repeatedly over long periods. A seminar discussed the physical principles behind solar radiation pressure and how it produces small forces on sails. Attitude control is needed to maintain the craft's orientation against various forces. Testing is challenging on Earth but applications could include satellites for trajectory corrections and missions close to the sun. Various sail configurations and materials have been proposed but deployment challenges have limited real-world testing until Japan's 2010 IKAROS mission, the first to use a solar sail as a primary propulsion system.

1. SEMINAR ON
SOLAR SAIL
BY
K.VISHNU
10427029

2. Introduction
Solar sails are also called light sail or photon
sail
Use radiation pressure for propulsion
Radiation pressure :- pressure excreted by
electromagnetic radiation
Can be used many times as they have
minimum moving parts
Total force excreted is around 1 Newton
making low thrust spacecraft

3. Physical principles
Solar radiation pressure
 Pressure on the sail due to reflection and small fraction is absorbed.
 Momentum of a photon is given by Einstein’s equation as p= E/c
where p  momentum, E  photon , c  speed of light
 Perfect sail perfect absorbance F= 4.54 μN/m2 , perfect reflectance
F=9.08μN/m2 and 100% specular reflectance.
 Due to wrinkles , absorbance ,curvature ,normal sail will have efficiency of 90%.
 Force on a sail is given by F = F0 cos2 θ / R2 (ideal sail)
θ angle bw sail force vector and radial from sun.
R distance from sun in AU.
 But for an actual sail ,force is F = F0 (0.349 + 0.662 cos 2θ − 0.011 cos 4θ) / R2
 Force and acceleration approach zero as θ nears 60o .

4. Attitude control
 Attitude  behavior of craft towards various force acting on it .
 It is maintained by ATTITUDE CONTROL UNIT (ACS) .
 Control is by changing crafts centre of pressure and centre of mass.
 achieved with control vanes, moments of individual sail etc.
 Along trajectory :- total force and torque changes.
 Sail temperature also changes with solar distance.
 ACS must be able support these changes.

5. Constraints
 Testing on earth is carried out at an altitude of 800km.
 Only at this height does solar pressure and drag pressure are typically equal.
Applications
 Solar sails can be used in space ships for both manned and unmanned voyages
(statite) .
 Solar sails can be used in satellites for trajectory corrections .
 thereby saving large amount of propellants.
 statite can go closer to sun ( up to distance were radiation pressure is equal to
gravity) .

6. Sail configurations
 Many sail configurations have been proposed like
 parachutes ; failed as it tends to collapse due to absence of rigid structure .
 square type.
 disk sail.
 In most cases angular momentum is used to stiffen the structures.
thereby eliminating the need for struts.
 In all cases , large amount of tensile stress is needed.
 weaker sails would ripple and cause structural damage .

7.  Latest developments include the use of electric and magnetic fields for
propulsion.
 Electric solar wind sail
electric solar wind sail use electric field generated by electrically charged wires
to deflect solar electron in light rays.
electric field is generated by straightened conducting wires placed around the
craft.
 Magnetic sail
 magnetic sail use magnetic field to deflect electrically charged particles.
 in both sails , maneuvering is achieved by changing the size and shape of their
respective fields.

8. Sail making
 Sails have been developed from many materials .
 Drexler developed a solar sail with thin aluminum film of .1mm thickness.
 The most common material used is aluminized 2µm kapton film.
 Solar sails made from alumina , carbon fiber , is found to be superior to aluminum,
or kapton films.
 New carbon fiber material is over 200 times thicker than conventional solar ail but
has the same mass.
 Lithium can also be used for sail making.
 In all cases , sail should be manufactured in space to avoid tearing during folding
and deployment and to reduce weight.

9.  Sails are mostly fabricated using vapor deposition and molecular manufacturing
techniques.
 Magnesium and beryllium can also be used for sail making.
 Reflection of light is preferred over absorption.
absorption exerts a force directed straight from sun which is not useful for high
performance sails.
absorption raises the equilibrium temperature in proportion to the fourth rot of
its absorptivity.

10. Projects operating or completed
 Until 2010, no solar sails had been successfully deployed in space as primary
propulsion system.
 In may 2010, Japanese space agency (JAXA) successfully launched IKAROS .
 IKAROS (Inter - planetary Kite – craft Accelerated by Radiation of Sun)
has a polyimide sheet of 200 m2
is diagonal spinning square sail 20m.

13. Conclusion
Though concept solar sail has developed for
many years , it is still in its infancy stage .

14. Reference
Wikipedia
space.com
seminarsonly.com