Slides on solar sails

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