Solar, Laser, Magnetic and Fission
Space Sails
By: Dr. Anton VanderWyst
Date: 26 June, 2014
Outline
Description of light sail concept
Solar powered
Laser powered
Plasma powered
Fission powered
One and two sail operation
Description of magnetic sail concept
Traditional magnet
Magnet size and power needs
Mini-magnetospheric plasma
propulsion (M2P2)
Particle beam propulsion
Issues associated with light sails
Sail material and missions
Sail mass and volume
Low thrust trajectories
Solar and laser power needed
Thermally limited acceleration
Instersteller dust impacts
Relativistic redshifting responses
Conclusion
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References
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Light sail concept
Propellant mass is the dominant concern in modern
space craft design. Propellantless methods of
space propulsion provide breakthrough
performance possibilities. They allow 92+% of the
mass to be removed.
The scientific and engineering challenges for this
category of space travel will be presented as well
as several unique proposed technological
responses.
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Solar powered sail
 Solar sails would propel a spacecraft by utilizing the pressure created by
the stream of photons (tiny units of light energy) from the sun.
 Once a spacecraft is in orbit, a lightweight sail would unfurl.
 Changing the position of the sail would increase or decrease speed.
 The thrust created by the photon stream is extremely low and interplanetary
journeys would take years [8].
5 year Earth-Mars trajectory
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Plasma and laser powered sails
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Plasma and laser powered sails II
 Avoid problem of miniscule solar
pressure by providing your own power
source.
 Require massive orbiting power
stations.
 Numerous ideas exist and have been
experimentally tested. They include a
magbeam [4] and focused plasma
beams [6].
 Ideas all exist at TRL 0-3.
 Have pointing accuracy and thermal
issues.
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Fission powered sail
The fission sail is a type of spacecraft propulsion proposed by Robert
Forward that uses fission fragments to propel a large solar sail-like craft.
a
plastic layer
b
radionuclides layer
f
neutralizer electron beam
 Defaults uses standard radioacitve decay & catches products
 A 10 kg instrument payload
could be sent to 250 AU in
10 years using 30 mg
of antihydrogen.
 Preliminary calculations predict 17 g of antihydrogen could send a similar
probe to the next star in 40 years.
 Isp = 1.4 million seconds
 Except … global antimatter production in all history: < 1g
 Current antimatter cost: $300 million / g
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One and two stage sails
 Sail design dictated by what you want to
do once you get to the destination.
 The easiest is a flyby, with a one stage
sail shooting back at maximum speed.
Would traverse the entire solar system
in <1 day, with ~3 minutes per planet
useful viewing time.
 To analyze a target, need to
stop upon arrival.
 Laser light from Earth (or a
transmitter in Earth orbit) would
be beamed at the sail. The first
(white) stage would focus and
redirect this light onto the
second (yellow) stage.
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Light sail analysis
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Sail mass and area
 To operate with minimal mass, the system spin- or three-axis- stabilized.
 Acceleration driven by areal density (sail loading). Great values are <1
g/m2. That gets you to the end of the solar system in ~20 years.
 

9.12 AOB m 2 cos 2  
hc
FSS N  
E photon[ J ]  h [ Hz ] 
m 2
2
c
R
AU

 s 
 Energy and force miniscule, where h = Planck’s constant = 6.63e-34 J-s.
 Teaser: momentum of a photon is where the school of quantum mechanics
first begins to emerge as a consequence of Debroglie's hypothesis. Total
energy is a function of wavelength.
 Effective areas are >> 10 km2.
 At 1/10th water density and 10 nm thick super-sail, could pack into 1 m3.
… and impossible to unfurl due to static electricity. Would shred if you
lightly blew on it.
 The lightest current 10 x 10 m sail placed 1 AU from the sun gives 3x10-12
N force, and accelerates at 1 picometer / s2. It would travel 1 meter in 13
days.
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Other uses for light sails
1) An antenna for communications, to
help focus radio transmissions from
earth
2) A dust detector – spacecraft are hit by
dust continually when in space, and the
number of dust impacts increase with
NASA ST5 antenna
size and speed. Solar sails can
measure the impacts via total energy
Fresnel lens
measurements.
3) Etching out parts of the solar sail
surface, and using that as antenna to
pick up radio waves. We'd use this as a
phased array radio receiver.
4) Make a Fresnel lens using an
interference effect.
5) NEO diversion [14]
Sample phased arrays
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Sail material and missions
Proposed sail materials are mylar,
aluminum, aluminized plastics or
nanotubes. Common thicknesses are
0.01 – 10 microns. Note a grain of salt
is 60 microns wide.
The boom uses temperature, UV or other
techniques to control rigidity. Most
designs use air to inflate it, but
maintain geometry in other ways.
There are supporting guy wires that
help keep it rigid. There is a problem
with tacking and changing directions.
Useful ranges for usage are 0.5-3 AU.
NASA’s New Millennium Missions
address needed technologies. Science
Technology 7-9 projects directed at
specific capabilities, such as booms,
unfolding and tacking.
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Solar Sail Missions:
 Launched Cosmos I sail in June
2005 aboard Russian Volna [5].
Sail size: 600 m2
 Launched NanoSail-D sail 2 Aug.,
2008 aboard SpaceX Falcon 1. Sail
size: 5 m2
 JAXA IKAROS, launched 2010,
spotted at 2 AU in May 2014
 Sunjammer, Falcon9 launch in
2015. Sail size: (124 ft) 1,200 m2
 Heliostorm. Tentative launch in
2018. Sail size: 22,500 m2
 Solar Polar Imager (SPI).
Tentative launch in 2027. Sail size:
22,500 m2
 Interstellar Probe. Sail size:
>100,000 m2
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Sail trajectories
 Modeling low, continuous thrust
trajectories is very difficult.
 The effect of acceleration is mm/s2,
so you cannot see it
 Unlike a rocket, very small
external perturbations need to
be accurately accounted for.
This includes the solar wind
variation, 2 planet gravitational
forces and interstellar particle
Brownian motion.
 Very large sails have differential gravitational
pulls across surface
 Need redundancy for cable breaks & possible
cell damage
 Can leverage existing electric propulsion
trajectory codes like SEPTOP [10].
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Pioneer 4 rocket trajectory
Earth-Mars EP trajectory
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Power needed
 Laser sails can provide greater power
density.
 Solar provides roughly 1.6 kW/m2 and
decreases  1/r2. Lasers can provide
TW/m2, which will vaporize the sail.
 Minimum focusing transmitter size is
when diffraction limited on receiver
Dr=2.44√L/Dt
where Dr is the receiver diameter, 2.44
is the first diffraction minimum (“Airy
Disk”),  is the laser power
wavelength, L is the distance and Dt is
the transmitter diameter. A 1 micron IR
beam fired from a 1,000 km-wide Earth
lens spreads out to 1,000 km receiver
by 43 LY away. At 4.3 LY, it is a 316
km wide sail.
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Rayleigh criterion dictates how the
effects of diffraction limit the size of
a spot you can focus onto an
object. As you move further away
from a highly collimated laser,
diffraction theory says that the spot
size must increase. However,
smaller wavelength = smaller spots
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Power needed, II
 Common needed space power ranges
are 0.01-100 TW (1010 – 1014 W).
• Total Earth average power is 15 GW
(1010 W)
 National Ignition Facility (NIF) at Law.
Livermore building world’s most
powerful laser, at 1.2 PW (1015 W)
Plaser 
M
sail
 M pay asailc
 spot 2nreflec   absorb 
 Would require 2-6 order of
magnitude increase in
power/weight ratio.
 The Space Shuttle engines
provide 164 kW/kg. That leads to
a 61,000-ton space laser.
 A full system mass to travel 40
LY is 210 billion tons (p. 104)
 The ISS is currently 287 tons
after 9 years and 26 dedicated
Shuttle flights.
 Airborne Laser (ABL) is MW-class.
amax
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
2n


4
4









T

T
reflec
absorb
SB
front
back
max
space

 absorb sailc
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Flight issues
Maximum acceleration limited by
radiation cooling limit. If any more
power was applied, the sail would
melt.
A fast moving sail therefore must:
• Be extremely light (low density )
• Have high backside emissivity 
• Possess high maximum temperature
During the years of flight operation,
(note Tmax << Tmelt due to thin film
there are a large variety of possible
agglomeration)
failure modes. They include:
• Have very high reflectivity reflec
 Deployment and tacking [13]
• Absorb minimal thermal energy 
 Thermal warping [11]
 Wobble control [12]
Could also power by microwaves
 Short circuits
closer, but cannot focus at a
 Solar radiation (solar wind)
distance.
 Erosion
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Interstellar debris impacts
 A light sail will impact space debris. While Dyson spheres and Bussard
interstellar fusion ramjets need such interactions, sails don’t appreciate
impacts at 0.5c (335 million mph).
 Interstellar hydrogen densities are roughly 1 atom / cm3 with 10-12 dust
particles / cm3. At full speed with a 10 km x 10 km sail, that is a travel
volume of 1023 cm3/ s = 1011 impacts / second.
 However, it isn’t all that bad, and you won’t lose thrust [15]. Key factors
are:
 Relative impact time. The dust takes
10-16 sec to travel through the sheet.
 No heat can be transferred.
 No tearing occurs – it punches
 Relative size of sail. Think how much
% dough a cookie cutter removes
 Dust impact severity highly depends
on travel through the local interstellar
cloud.
Space Sails
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Relativistic redshift impacts





The much greater problem is the substantial growth in
power needed as the sail velocity increases. The
redshift effect kills us at 0.5c due to
Change in laser output wavelength to 3x the starting
frequency
2nd stage rendezvous stage size increase of 200%
Laser power increase of 73%
Sail diameter increase of 31%
Sail mass increase of 15%


r
M

Mr
V
1
c
V
1
c
1
V2
1 2
c
 Can get greater force by increasing the
frequency of the photon and increasing its
probability of reflection.
 If it were possible to develop an ultra light
weight material that reflects x-rays, it
would be possible to focus a smaller spot
on the solar sail from earth based lasers.
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Light sail review
Light sails, whether powered by natural solar or manmade lasers, have a
specific niche they occupy in space propulsion. Their benefits include:
• No onboard propulsion needed means a very wide variety of possible
space missions become feasible.
• Scalable.
• Sail itself is reasonable cost.
• Already launched four, so base technology is very well understood and
possesses a high TRL.
Difficulties:
• Power needs for even small missions rapidly become exorbitant.
• Cannot currently make a structure that is light enough. System
performance dictated by sail density.
• Releasing, unfolding and steering are difficult.
• Supporting infrastructure needs exponentially grow.
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Magnetic sail analysis
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Standard magnetic sail
 The magnetic sail is a use of Lenz’s Law
(flux will attempt to remain constant in a
electrified wire loop).
 The loop should be made from
superconducting wires, and will expand to a
circle when powered.
 The craft will be attached to this loop.
 Charged particles meeting the loop or
magsail at other angles than parallel to the
magnetic field will transfer some of their
momentum to the field and thus push the craft.
 A magsail weighing 36 tons could receive
accelerations of 0.1 mm/s2 to 9 mm/s2; varying
with the sail orientation.
 The magnetic loop is very small compared to
a standard light sail, being only about 10 km in
diameter.
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Supersized magnetic sail





World record magnetic field is >37 T [16]
Earth’s field is 30-60 T (0.3-0.6 Gauss)
World record current density is > 7e8 [A/m2]
World record current is 20 kA at CERN
National High Field Magnetic Laboratory
has 21 T, 5 m tall, 13 ton, 40 MJ magnet.
 Problem is that to create a large field
requires
‒ Very large and heavy magnets
‒ Energy replacement due to charge loss
 Result is cannot get a large enough mag.
field cheaply enough [17]
Thrust
thrust 10
AU
thrust 100
AU
Mass
[N]
[N]
[N]
[MT]
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radius
Start
energy
Energy
loss/day
Battery mass/day
[km]
[MJ]
[MJ]
[kg]
3
0.1
0.00
0.1
6
6,194
149
74
9
0.4
0.00
0.5
10
9,252
222
111
27
1.2
0.01
1.4
18
13,344
320
160
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Mini magnetospheric plasma propulsion
 To reduce the cost of increasing
the magnetic field radius, Mini
magnetospheric plasma propulsion
(M2P2) has been introduced.
 M2P2 still uses magnetic fields to
create a large barrier to incoming
particles and plasmas. The
reflection of those energy fields
allow very low propellant
propulsion.
 However, it injects low-energy
plasma to artifically generate a
mini-magnetosphere [2].
 This locally stronger magnetic
field results in Isp ~35,000
seconds [1].
clip
clip
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Particle beam behavior
Space particle beams can be used
in magsails [18]. Benefits include:
 ISPs [15,000 – 45,000] range
 Suited for interstellar precursor
miss.
Problems include:
 Requires a dedicated beamed
momentum source
 Particles hit a pusher plate or
reflect of EM wall
 Beam can be deflected by solar
magnetic fields.
 Relativistic velocities make
closed-loop control impossible.
 Neutral particles are unaffected
by EM fields
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Particle beam generator
MagSail operation
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Conclusions
 Several different ‘no to minimal’ propellant methods of imparting
momentum to space vehicles have been presented.
 Solar, laser, fission, magnetic and particle beams have been examined.
 The state of the art, future programs, benefits and challenges have been
identified.
 Each of these approaches has already been ground tested and shows
appreciable promise for Moon to the edge of solar system missions.
 All require substantial additional scientific and engineering development
before they become common methods of intersolar propulsion.
 The minimal propellant needed enables a large variety of missions,
spanning the thrust and time ranges.
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References
[1] Winglee et al., “Simulation of mini-magnetospheric plasma propulsion (M2P2) interacting
with an external plasma wind”. AIAA Joint Propulsion Conference, 2003.
[2] Mini-Magnetospheric Plasma Propulsion (M2P2) Space propulsion group at the University of
Washington. http://www.ess.washington.edu/Space/M2P2 /technical.html
[3] Winglee et al., “M2P2: tapping the energy of the solar wind for spacecraft propulsion”. J.
Geophysical research, 150(A9) p. 21067, Sept. 2000.
[4] Winglee, R. and Ziemba, T. “MagBeam phase I final report for NASA institute for advanced
concepts”. 30 April 2005.
[5] Cosmos I, launched by the Planetary Society in 2005.
http://www.planetary.org/programs/projects/solar_sailing/
[6] http://www.nas.nasa.gov/About/Education/SpaceSettlement/SolarSails/links.html
[7] http://www.space.com/common/media/video/player.php?videoRef= LS_090519_SpaceEngines
[8] McInnes, C. R. Solar Sailing: Technology, Dynamics and Mission Applications. SpringerVerlag, 1999.
[9] http://sail.quarkweb.com/light.htm
[10] Woodcock, G. R. and Dankanich, J. “Application of solar-electric propulsion to robotic and
human missions in near-Earth space”. AIAA 2006-4464, JPC 10 July 2006.
[11] Endicter, J. et. al. “GOES-I/M yaw momentum anomaly analysis and recovery”, SpaceOps
AIAA 2008-3422. 2008.
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References, II
[12] Bajora, A. and Arora, N., and Globus, A. “Kalpana one: a new space colony design”. Space
Knowledge, On Orbital Space Settlement #06. 1 Nov. 2007.
[13] Herbeck, L. et. al. “Development and test of deployable ultra-lightweight CFRP-booms for a
solar sail”, European Conf. on Spacecraft Structures, ESA SP-468 Mar. 2001.
[14] Dachwald, B. and Wie, B. “Solar sail trajectory optimization for intercepting, impacting and
deflecting near-Earth asteroids”, AIAA 2005-6176, San Francisco, CA 2005.
[15] Frisbee, R. H., “Beamed-momentum lightsails for interstellar missions: mission applications
and technology requirements”, AIAA 2004-3567, 11 July 2004.
[16] Asano, T. et. al. “resistive insert magnet for a 37.3-T hybrid magnet”, Physics B:
Condensed Matter, 294, pp 635-638, Jan. 2001.
[17] http://www.sjgames.com/gurps/Roleplayer/Roleplayer29/MagSails.html
[18] Bishop, F. “Some novel space propulsion systems”, J. Aircraft Engineering and
Aerospace Technology, 75:3, pp. 247-255. 2003.
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