1. Ultra-Light Solar Sail
1
Pioneer Astronautics
for
Interstellar Travel
Phase I
Presented to:
NIAC
November 9, 1999
Dean Spieth
Pioneer Astronautics, Inc.
Dr. Robert Zubrin, President, (303) 980-0890
445 Union Blvd. #125
Lakewood, Colorado 80228

2. 2
(Not drawn to scale)
Pioneer Astronautics
SSccooppee ooff PPhhaassee II Woorrkk
• Objective
– Analyze Capabilities of an Ultralight Solar Sail Using a Nanogrid of
Reflector Material without a Plastic Backing (Similar to a Nanoscale
Antenna Mesh).
• Approach
– Develop Equations for the Reflectivity of a Nanogrid of Wires.
– Analyze Engineering Constraints of Dimensions and Strength.
– Address Operational Issues of Deployment and Control.
– Determine Manufacturing Technologies Required for Fabrication.
– Develop a Phase II Plan to Demonstrate Key Fabrication
Technologies and Verify Basic Concepts.
– Present Briefing and Final Report.

3. PPhhyyssiiccss IIssssuueess
• Develop Equations for the Solar Reflectivity Off a Nanogrid.
– Rigorous Treatment
– Compare to Lower Frequency Treatments by Marcuvitz (1951) and
Forward (1985), Extrapolated to Visible
• First, Obtain a Baseline for the Solar Reflectivity Off a Solid
Sheet without a Plastic Backing.
3
Reflectance
Transmittance
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1
0.8
0.6
0.4
0.2
0
0 0.005 0.01 0.015 0.02 0.025 0.03
Fraction Reflected or Transmitted
Thickness, microns

4. Naannoossccaallee Alluumiinnuum SShheeeettss Acchhiieevvee aacc~~00..33 m//ss22
• Although Reflectivity Reaches a Maximum Above 30 nm
Thickness, an Optimum Thrust-to-Mass Ratio (i.e.,
Acceleration) of ~0.3 m/s2 Occurs at Only a Few Nanometers
Thickness at 1 AU.
4
0.2 AU
1 AU
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10
1
0.1
0.01
0.001
0 0.005 0.01 0.015 0.02 0.025 0.03
Sail Acceleration, m/s2
Thickness, microns

5. Muullttii--wiirree Annaallyyssiiss Reessuullttss iinn aacc >> 00..5544 m//ss22
• Solution of Maxwell’s Equations for Reflection Off a Grid of
Wires with Finite Electrical Conductivity (see Progress Report
#3, October 1999).
• Best Acceleration: Radius = 5 nm, Interwire spacing = 50 nm
– Not yet optimum, due to convergence issues at other values
Scatter Plot of Wire Grid Accelerations
0.45
0.32
0.1 1 10 100
Wire Radius, r, nm
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1000
100
10
Wire Spacing, s, nm
(Analysis by Dr. Cindy R. Christensen)
0.30
0.37 0.43
0.54 m/s2
0.53
0.34
0.33
0.31
0.20 0.10

6. Muullttii--wiirree RFF Annaallooggyy Reessuullttss iinn aacc ~~55 m//ss22
• Extension of Marcuvitz’s (1951) Equations from Microwave to
Visible Frequencies, with Uncoupled Thickness Factor, see p 3.
• Close Agreement with Forward’s (1985) Equations for s/r<20.
• Yet >10X Higher Than Christensen’s Analysis.
• Resolve Discrepancies via Fab and Test in Phase II.
Sail Grid Acceleration vs Wire Spacing to Radius Ratio
6
s/r = 100
s/r = 50
s/r = 10
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5
4
3
2
1
0
0 0.001 0.002 0.003 0.004 0.005
Sail Acceleration, m/s2
Wire Radius, microns

7. Caarrbboonn Naannoottuubbeess aass ““Hoolllloow”” Wiirreess
• Start Out Analysis with “Hollow” Wires.
– For graphite, best thrust to mass is 0.18 m/s2.
» DC conductivity of nanotubes is only half that of bulk aluminum
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• Then Dope the Graphite Nanotubes.
– With doping, conductivity is greatly enhanced, Dekker (1999).
– Best Answers: Radius = 1.38 nm, Spacing = 100 nm
Thrust to mass: 18 m/s2
• Conductively Coated or Doped Carbon Nanostructures Show
Great Promise in the Far Term, for Its Low Mass and High
Temperature Characteristics.
(Analysis by Dr. Cindy R. Christensen)

8. EEnnggiinneeeerriinngg Coonnssiiddeerraattiioonnss
• Aluminum Foil Rips Rather Easily, and is 10,000X Thicker Than
1 to 10 nm Thick Ultrathin Solar Sails Analyzed.
• Can We Apply This Sheet or Mesh on a Plastic to Avoid Ripping
for Handling, Storage, Launch, and Deployment, Then Allow the
Plastic to Disintegrate or Outgas Once in Space?
– Aluminized Mylar is Space Qualified, although with 100 nm Coating
– Low E Coatings for Windows Involve nm Thick Coatings
– Is There a Simpler Solution Than Using a Diamond-Like Coating
Buffer Layer?
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• Once Deployed in Interplanetary Space:
– Metals are Very Stable to Radiation, Unlike Plastics
– As Approach Sun, Perhaps Eventually to 0.2 AU
» Plastic Support Membrane Disappears - Must Cover Critical Payload
Surfaces (Optics & Thermal Control) from Contamination
» Avoid Outgassing/ Melting of Aluminum with Solar Approach
» Watch Reduction in Tensile Strength with Temperature

9. UUllttrraatthhiinn AAlluumiinnuum SSaaiillss CCaann SSuurrvviivvee SSoollaarr AApppprrooaacchh
• Ultrathin Sheet of Aluminum Can Survive Solar Equilibrium
Temperature at 0.2 AU.
• Desirable αααα////εεεε Ratio for Thermal Control at a Few Nanometers
Thickness. (Similar trends as for chromium, which is recommended
on backside of conventional solar sail, i.e., emittance increases as
approach nanometers thickness.)
Temperature of Aluminum Sheet vs Solar Distance
9
2 nm aluminum film,
absorptivity
solar
= 0.19,
emissivity
IR
= 0.28
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1000
800
600
400
200
0
Aluminum
Melts
0 0.2 0.4 0.6 0.8 1
Sail Temperature, oC
Distance from Sun, AU

10. UUllttrraatthhiinn AAlluumiinnuum CCaann SSuurrvviivvee SSoollaarr RRaaddiiaattiioonn PPrreessssuurree
• Sail Radius of Curvature rc Must Be < 1 km for Sheet @ 0.2 AU.
• Aluminum Grid Can Also Likely Survive Stresses.
100
10
1
0.1
0.01
Aluminum Tensile Strength versus Temperature
1100 Al-O
6061 Al-T6
10
Tensile Stress versus Sail Thickness and Curvature @ 0.2 AU
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0.001
= 1 km
r
c
0.001 0.01 0.1 1 10
Sail Tensile Stress, ksi
Sail Thickness, microns
r
c
= 10 km
r
c
= 0.1 km
40
35
30
25
20
15
10
5
0
0 50 100 150 200 250 300 350 400
Tensile Strength, ksi
Temperature, oC

11. 11
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Oppeerraattiioonnaall IIssssuueess
• Deployment and Control in Space
– Deployment Comparable to Conventional Sail, as Strong Plastic
Substrate is Intact During Deployment
– Control Possibly Using Conventional Sail Technology
Comet Halley Concept (NASA/JPL)

12. 12
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Maannuuffaaccttuurriinngg IIssssuueess
• Manufacture in Space
– Conceivable But Far Into the Future
– Sail Size Can Be Much Larger than Manufactured Size on Earth
» Analogy to Spider Web in-situ Fabrication
• Manufacture on Earth
– Substrate
» Low Temperature, Thin Plastic
– Reinforcement
» Kapton Tape
» Embed High Temperature Netting with High Tensile Strength
– Coating
» Several Nanometers of Aluminum
» Examples: Aluminized Mylar or Kapton, or Window Film
– Patterning
» e-Beam Lithography is Now Approaching Needed Scale
» Laser Drilling Scale May Be Too Large
Note: Nanotubes are also Under Development

13. 13
Pioneer Astronautics
Miissssiioonn Annaallyyssiiss
• Near-Term (within 10 years)
– nm Thin Aluminized Plastics, With Sail Plastic Disintegration,
Reinforced with Kapton Tape and High Strength Cord
– Within 0.2 AU of Sun with Accelerations ~10 m/s2 (ac~0.3 m/s2)
– Several Hundred Times Better Than Conventional Solar Sails with
Only 2 micron Thick Kapton
• Mid-Term (within 20 years)
– Large Scale Nanopatterning of Mesh-like Grid on Plastic
– Characteristic Accelerations ac~ 1 m/s2, Analysis Ongoing
• Far-Term (beyond 20 years)
– Large Scale Grid of Doped Carbon Nanotubes
– Manufacture in Space Above 1000 km (to avoid drag & atomic O)
– Solar Approach within 4 Rs (0.019 AU) and ac> 10 m/s2

14. Miissssiioonn TTiimeess ttoo IInntteerrsstteellllaarr SSppaaccee
• In Near-Term, Could Reach Pluto in ~100 days.
• In Mid-Term, Can Reach JPL Goal of 35 yrs for 10,000 AU Probe
– Table Below Shows 27 yrs for 1 m/s2 from 0.1 AU to 10,000 AU
– Assumes Improvements in Mesh Technology (Phase II)
• Far-Term Technology, Possibly Using Carbon Nanotubes, May
Reach 10,000 AU in 4 Years! Or α Centauri in a Century!
Acceleration
@ 1 AU with
Payload,
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m/s2
Closest
Solar
Approach,
AU
Terminal
Velocity,
km/s
40 AU
Pluto
Mission,
days
10,000AU
Mission,
yrs
0.3 0.2 671 102 71
1.0 0.1 1,733 40 27
10 0.019
(4 Rs)
12,572
(4.2%c)
6 4

15. 15
Pioneer Astronautics
PPhhaassee IIII PPrrooppoosseedd TTaasskkss
• Task 1 - Nanometer Class Solar Sail Sheet
– Vacuum Deposit 2, ..., 10 nm Thick Films on Plastic Substrate.
– Attempt Plastic Decomposition in Thermal-Vacuum Chamber.
– Measure Optical & Mechanical Properties After Test, to Verify Over
100X More Acceleration Than Conventional Sail Technology.
• Task 2 - Nanometer Grid Reflector Solar Sail
– Update Nanogrid Analysis for Various Geometries and Materials.
– Pattern Grid Using e-beam Lithography or UV Lasers.
– Measure Solar Absorptance, BRDF, Emittance versus Grid
Geometry.
• Task 3 - Fastener and Rip Stops - Integrate with Sail so It Does
Not Decompose.
• Task 4 - Carbon Nanostructures Solar Sail Analysis.
• Task 5 - Final Report & Update Interstellar Mission Implications.

16. SSuummaarryy
• Ultralight Aluminum Solar Sails, without a Plastic Backing,
Have Orders of Magnitude Improvement Over Conventional
Solar Sails with a Plastic Backing.
• High Characteristic Accelerations @ 1 AU
– Thin Aluminum Membranes ~0.3 m/s2 vs 0.001 m/s2 Conventional
– Aluminum Nanowires ~0.6 m/s2, Possibly Much Higher
– Doped Carbon Nanotubes >10 m/s2
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• Fantastic Velocities to Interstellar Space
– Aluminum Membranes to ~1000 km/s – 10,000 AU within a Lifetime
– Carbon Nanostructures Possibly to ~4%c, α Cen in a Century
• Strong Experimental Program Recommended
– e-Beam Lithography of Nanoscale Reflectors
– Optical Measurements of Fabricated Reflectors
– Thermal-Vacuum Tests with Enhanced UV & Heat to Ascertain
Clean Removal of Various Plastics

17. Keeyy Reeffeerreenncceess
• N. Marcuvitz (1951), Waveguide Handbook, MIT Rad. Lab. Ser. ,
McGraw-Hill, New York, p 286.
• W.M. Rowe, et. Al. (1978), “Thermal Radiative Properties of
Solar Sail Film Materials,” AIAA Paper 78-852.
• Robert Forward (1984), “Roundtrip Interstellar Travel Using
Laser-Pushed Lightsails,” J. Spacecraft and Rockets, Vol. 21,
No. 2, pp 187-195.
• Robert Forward (1985), “Starwisp: An Ultra-Light Interstellar
Probe,” J. Spacecraft and Rockets, Vol. 22, No. 3, pp 345-350.
• Robert Forward (1990), “Light-Levitated Geostationary
Cylindrical Orbits: Correction and Expansion,” J. Astronautical
Sci., Vol. 38, No. 3, pp 335-353.
• C.R. McInnes (1999), Solar Sailing, Praxis Publishing, UK.
• Cees Dekker (1999), “Carbon Nanotubes as Molecular Quantum
Wires,” Physics Today, May 1999.
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