921buhler[1]

Analysis of a Lunar Base Electrostatic Radiation Shield Concept

Charles Buhler, PI John Lane, Co-PI ASRC Aerospace Corporation Kennedy Space Center, Florida 32899

INTERPLANETARY RADIATION ENVIRONMENT Main Components: (Atomic Nuclei)

Galactic Cosmic Ray Spectra 4000

Galactic Cosmic Rays (GCRs)

• •

3500

Solar Maximum Solar Minimum

#/m2-s-sterradian

¾

3000 2500

Median energy ~1800 MeV/nuc Continuous flux, varies with the solar cycle

2000 1500 1000 500 0 10

100

1000

Energy (MeV/nucleon)

¾

Solar Energetic Particles (SEPs)

• •

Sporadic, lasting hours to days Soft spectra with highly variable composition

ni~ne~ 6 cm-3

10000

100000

Lunar

From Francis Cucinotta, NASA JSC Space Radiation Health Project (private communication)

Shielding Solutions must • • • • •

Reduce radiation exposure Be lightweight Safe Practical Achievable in time for Moon Missions

There are two basic types: Active and Passive Shields

Spacecraft Limitations Passive shielding can reduce the exposure by only about a factor of two due to weight constraints.

Polyethylene Solar Minimum

John W. Wilson et al.

NASA Technical Paper 3682 (1997)

Active Shielding Solutions • Electromagnetic Shields – Magnets (>73 papers since 1961) – Plasma (>18 papers since 1964) – Electrostatic (>16 papers since 1962) Traditional Spacecraft Design Cosmic Ray +

+

+

+ Shielding + Volume E

a

+ + b

Slides provided by Jim Adams, Langley

Concentric, oppositely charged spherical electrodes for shielding against galactic heavy ions.

Electrostatic generator keeps ‘a’ at a high voltage with respect to ‘b’.

Why Not Electrostatics?

– Debye Length ~11.5m • Assumption: The charge on a conductor is much lower than the charge in the surrounding volume.

– Extreme voltages are required and surrounding a spacecraft or lunar base with a conducting shell is not realistic • The same effect can be generated using an alternate geometry.

NASA Design “Protected Zone” Center Sphere at +V0

-3 V1

- V1

2 spheres at +2V2 2 spheres at +3V2

+2V2

-3 V1

+2V2 - V1

5 at -2V1

5 at -2 V1

5 m radius 30 m

100 m

Radiation Intensity

Radiation Fluence: No Shielding

GCR

From Space

From the Sun 0.1

1

10

SPE 100

Particle Energy [MV]

1000

10000

Radiation Fluence: No Shielding

Radiation Intensity

Solar “Storm” – lasting hours to days SPE GCR

0.1

1

10

100

Particle Energy [MV]

1000

10000

Radiation Fluence: No Shielding SPE

Radiation Intensity

Solar “Storm” – lasting hours to days

GCR

0.1

1

10

100

Particle Energy [MV]

1000

10000

Radiation Intensity

Radiation Fluence: No Shielding

SPE GCR

0.1

1

10

100

Particle Energy [MV]

1000

10000

Radiation Intensity

Radiation Fluence: No Shielding

GCR

SPE 0.1

1

10

100

Particle Energy [MV]

1000

10000

An Electrostatic Shield Design

Some Possible Electrode Geometries

Thin Film Polymer with Conductive Inner Coating

Conductive Mesh Screen

Conductive Wire Mesh Sphere

Arbitrary Geometry

Electrode Geometry Used in ASRC Lunar Electrostatic Shield Model (LESM)

Thin Film Polymer Balloon with Conductive Inner Coating

Theory of Design Lorentz Force

F = qE + qv Ă— B

Theory of Design Coulomb Force

F = qE + qv Ă— B

Theory of Design Coulomb Force

F = qE Electrostatic Shield: Use only a time independent &= 0 electric field, i.e., E

Design Strategy Determine an Ideal Electric Field to Repel Charged Particle Radiation (primarily positive ions and electrons)

STEP 1:

E( x , y , z )

Design Strategy STEP 2:

Find a Way to Generate an Approximation of the Ideal Field

Design Strategy STEP 3:

Perform Mathematical Modeling and Computer Simulation of Proposed Configurations

Design Strategy STEP 4:

Perform Experiments and Testing on a Scale Model Particle Detector

Lunar Shield Model Under Test High Vacuum Chamber

P ∈ {10−5 ,10−10 } [torr]

Accelerator Grid

∆V ∈ {102 ,104 } [volts] Ion Selector

Ion Source

Broad-Band Energy Distribution to Simulate SPE Distribution

An Electrostatic Shield Design

Electrostatic Shield Design Constraints Electrical Non-Electrodes • Electric Field Strength everywhere must remain well below a breakdown threshold value: E ( x , y , z ) < E B ( x, y , z ) In the case of non-conductors, EB(x, y, z) is related to the Dielectric Strength of the materials subjected to E(x, y, z).

Electrodes • Surface Charge Distribution must remain well below a threshold breakdown value: σ ( x, y, z ) < σ B ( x, y, z ) In the case of conductors, when σ (x, y, z) exceeds σB(x, y, z), the Coulomb force expels charge from the surface of the conductor.

Electrostatic Shield Design Constraints E ( x , y , z ) > E B ( x, y , z )

Electrostatic Shield Design Constraints

E ( x , y , z ) > E B ( x, y , z )

This Geometry Violates Physical Constraints

Electrostatic Shield Design Constraints Mechanical Forces â&#x20AC;˘ The Coulomb forces between electrodes must not exceed the mechanical strength of the materials. In the case of thin film polymers, for example, the tensile strength can not be exceeded.

Size and Weight â&#x20AC;˘ Size and weight are limited by considerations related to transportation to the lunar surface and by practical assembly and construction activities.

Electrostatic Shield Design Constraints Power, Dust, and X-Rays Power • Collision of charged particles with electrodes leads to a current, which must be minimized in order to constrain power requirements.

Surface Dust and Free Electrons • The design must avoid attraction of surface dust and electrons to the high voltage electrodes.

Brehmsstrahlung X-Rays • Solar wind electrons accelerated by high voltage positive electrodes, must not be allowed to decelerate due to collisions with the electrodes.

Four Positive Sphere Electrodes

Front View of Lunar Habitat and Positive High Voltage Shield

Φ (z ) [MV]

100

100

50

10

z [m]

0

− 100

Voltage Potential Profile – Assume: Grounded Surface

Φ (z ) [MV]

100

100 z [m]

50

10

0

SPE Shield (little effect on GCRs)

− 100

Voltage Potential Profile – Assume: Grounded Surface

Radiation Flux: Grounded Lunar Surface +100 MV Shield

Radiation Intensity

SPE

GCR

0.1

1

10

100

Particle Energy [MV]

1000

10000

Φ (z ) [MV]

100

100

50

z [m]

0

− 100

Voltage Potential Profile – Assume: Floating Surface

Φ (z ) [MV]

100

100 z [m]

50

0

SPE & Miminal GCR Shield (some effect on GCRs)

− 100

Voltage Potential Profile – Assume: Floating Surface

Radiation Flux: Floating Lunar Surface +100 MV Shield

Radiation Intensity

SPE

GCR

0.1

1

10

100

Particle Energy [MV]

1000

10000

Φ (z ) [MV]

100

100

50

10

z [m]

0

− 100

Voltage Potential Profile – Ground Ground Shield

Φ (z ) [MV]

100

100 z [m]

50

10

0

SPE Shield only – best for dust?

− 100

Voltage Potential Profile – Ground Ground Shield

Φ (z ) [MV]

100

100

50

10

z [m]

0

− 100

Voltage Potential Profile – Use B Field to Shield Electrons

Passive Shield to Stop Low Angle Particle Trajectories

If the lunar surface is zero potential, i.e., electrical ground

SPE

Radiation Fluence, Shield Transmission, Biological Response, and Dosage F (E )

ξ (E )

1 − ξ (E)

Shield Efficiency

Shield Transmission

Radiation Intensity

Biological Response

R(E )

0.1

1

10

100

Particle Energy [MV]

1000

10000

SPE

Radiation Fluence, Shield Transmission, Biological Response, and Dosage F (E ) Shield Efficiency

Radiation Intensity

Biological Response Dosage (without Shielding):

D0 ≈ ∫ F ( E ) R( E )dE

0.1

1

10

R(E )

100

Particle Energy [MV]

1000

10000

SPE

Radiation Fluence, Shield Transmission, Biological Response, and Dosage F (E ) 1 − ξ (E)

Radiation Intensity

Biological Response Dosage with Shielding:

D ≈ ∫ (1 − ξ ( E ) )F ( E ) R( E )dE

0.1

1

10

R(E )

100

Particle Energy [MV]

1000

10000

Define a Shielding Quality Factor SPE F (E ) 1 − ξ (E)

Radiation Intensity

Biological Response Shielding Quality Factor:

QS ≡ 1 −

0.1

1

D D0

R(E )

10

100

Particle Energy [MV]

1000

10000

Test Configuration -50 MV

-50 MV

-50 MV -50 MV

+150 -50 MV

+150

-50 MV

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) â&#x20AC;&#x201C; User Interface and Sphere Configuration File Shield OFF (unpowered)

Sphere Configuration File Shaded Entries Correspond To Image Charges Below Lunar Surface 20

Number of Spheres

V [MV] R [m] x [m] y [m] z [m] ========================================== 150.0 3.0 5.0 0.0 8.0 150.0 3.0 -2.5 4.33 8.0 150.0 3.0 -2.5 -4.33 8.0 -50.0 4.0 10.0 0.0 12.0 -50.0 4.0 -5.0 8.66 12.0 -50.0 4.0 -5.0 -8.66 12.0 -50.0 5.0 0.0 0.0 16.0 -50.0 4.0 -15.0 0.0 8.0 -50.0 4.0 7.5 12.99 8.0 -50.0 4.0 7.5 -12.99 8.0 -150.0 3.0 5.0 0.0 -8.0 -150.0 3.0 -2.5 4.33 -8.0 -150.0 3.0 -2.5 -4.33 -8.0 50.0 4.0 10.0 0.0 -12.0 50.0 4.0 -5.0 8.66 -12.0 50.0 4.0 -5.0 -8.66 -12.0 50.0 5.0 0.0 0.0 -16.0 50.0 4.0 -15.0 0.0 -8.0 50.0 4.0 7.5 12.99 -8.0 50.0 4.0 7.5 -12.99 -8.0 ==========================================

Shield OFF (unpowered)

x-y, z = 0 plane

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) â&#x20AC;&#x201C; Red dots are intersection of electrons and blue dots are intersection of protons with lunar surface (z = 0). Gray circles are x-y projections of unpowered electrostatic spheres.

Shield OFF (unpowered)

Protected Region

x-y view

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) â&#x20AC;&#x201C; Red dots are intersection of electrons and blue dots are intersection of protons with a 4 [m] radius sphere (protected area) centered at x = 0, y = 0, z = 0. Gray circles are x-y projections of unpowered electrostatic spheres. Yellow-gray trails are particle trajectory paths.

Shield OFF (unpowered) Φ=0

y-z view

Lunar surface

Protected Region

Φ=0

Image Spheres

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) – Red dots are intersection of electrons and blue dots are intersection of protons with a 4 [m] radius sphere (protected area) centered at x = 0, y = 0, z = 0. Gray circles are y-z projections of unpowered electrostatic spheres. Yellow-gray trails are particle trajectory paths.

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) â&#x20AC;&#x201C; User Interface and Sphere Configuration File Shield ON (powered)

Sphere Configuration File Shaded Entries Correspond To Image Charges Below Lunar Surface 20

Number of Spheres

V [MV] R [m] x [m] y [m] z [m] ========================================== 150.0 3.0 5.0 0.0 8.0 150.0 3.0 -2.5 4.33 8.0 150.0 3.0 -2.5 -4.33 8.0 -50.0 4.0 10.0 0.0 12.0 -50.0 4.0 -5.0 8.66 12.0 -50.0 4.0 -5.0 -8.66 12.0 -50.0 5.0 0.0 0.0 16.0 -50.0 4.0 -15.0 0.0 8.0 -50.0 4.0 7.5 12.99 8.0 -50.0 4.0 7.5 -12.99 8.0 -150.0 3.0 5.0 0.0 -8.0 -150.0 3.0 -2.5 4.33 -8.0 -150.0 3.0 -2.5 -4.33 -8.0 50.0 4.0 10.0 0.0 -12.0 50.0 4.0 -5.0 8.66 -12.0 50.0 4.0 -5.0 -8.66 -12.0 50.0 5.0 0.0 0.0 -16.0 50.0 4.0 -15.0 0.0 -8.0 50.0 4.0 7.5 12.99 -8.0 50.0 4.0 7.5 -12.99 -8.0 ==========================================

Shield ON (powered)

x-y, z = 0 plane

Φ = −50 MV Φ = 150 MV

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) – Red dots are intersection of electrons and blue dots are intersection of protons with lunar surface (z = 0). Gray circles are x-y projections of powered electrostatic spheres.

Shield ON (powered)

Protected Region

x-y view

Φ = −50 MV Φ = 150 MV

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) – Red dots are intersection of electrons and blue dots are intersection of protons with a 4 [m] radius sphere (protected area) centered at x = 0, y = 0, z = 0. Gray circles are x-y projections of powered electrostatic spheres. Yellow-gray trails are particle trajectory paths.

Shield ON (powered) Φ≠0

y-z view

Φ = −50 MV

Lunar surface

Protected Region

Image Spheres

Φ = 150 MV

Φ=0

Φ = 50 MV Φ = −150 MV

Simulation Run of Lunar Electrostatic Shield Model (LESM v1.2) – Red dots are intersection of electrons and blue dots are intersection of protons with a 4 [m] radius sphere (protected area) centered at x = 0, y = 0, z = 0. Gray circles are y-z projections of powered electrostatic spheres. Yellow-gray trails are particle trajectory paths.

Model Simulation Results Four Electrostatic Spheres and One Magnetic Field Coil

Spherical Solenoid

Simulation Run of Lunar Electrostatic Shield Model (LESM v2.3) â&#x20AC;&#x201C; User Interface and Sphere Configuration File Shield ON (powered)

Sphere Configuration File Shaded Entries Correspond To Image Charges Below Lunar Surface 8

Number of Spheres

V [MV] R [m] x [m] y [m] z [m] ======================================== 100 4.0 0.0 0.0 25.0 50 4.0 8.66 5.0 20.0 50 4.0 -8.66 5.0 20.0 50 4.0 0.00 -10.0 20.0 -100 4.0 0.0 0.0 -25.0 -50 4.0 8.66 5.0 -20.0 -50 4.0 -8.66 5.0 -20.0 -50 4.0 0.00 -10.0 -20.0 ========================================

Model Simulation Results: x-y Plane Two 30 MeV Protons and Two 1 MeV Electrons

E≠0 B≠0

Model Simulation Results: x-z Plane Two 30 MeV Protons and Two 1 MeV Electrons

E≠0 B≠0

Lunar Surface

Model Simulation Results: y-z Plane Two 30 MeV Protons and Two 1 MeV Electrons

E≠0 B≠0

Lunar Surface

E = off B = off

E = off B = off

E = on B = off

E = on B = on

E = off B = on

Model Simulation Results: x-y Plane 30 MeV Protons, 1 MeV Electrons E=0 B=0

Model Simulation Results: x-z Plane 30 MeV Protons, 1 MeV Electrons E=0 B=0

Lunar Surface

Image Spheres

Model Simulation Results: y-z Plane 30 MeV Protons, 1 MeV Electrons E=0 B=0

Lunar Surface

Image Spheres

Model Simulation Results

8m

20 m

25 m

One +100 MV Sphere and Three +50 MV Spheres

Habitat Protected Volume

Model Simulation Results 30 MeV Protons, 1 MeV Electrons

electrons protons

E=0 B=0

Habitat Protected Volume

Model Simulation Results 30 MeV Protons, 1 MeV Electrons

Eâ&#x2030; 0 B=0

electrons protons

+100 MV

+50 MV

+50 MV +50 MV

Habitat Protected Volume

Model Simulation Results Brehmsstrahlung X-ray Emission

Eâ&#x2030; 0 B=0

electrons protons

+100 MV

+50 MV

+50 MV +50 MV

Habitat Protected Volume

Model Simulation Results 30 MeV Protons, 1 MeV Electrons Bmax ≈ 0.5 [T] E≠0 B≠0

+100 MV

+50 MV

electrons protons

i = 1000 A

+50 MV +50 MV

Habitat Protected Volume

Mathematical Model Electric Field Due to a System of Conducting Spheres The field due to a system of N point charges at a field point r is:

E(r ) =

1 4πε 0

r − ri

N

∑ qi i =1

r − ri

3

(1)

where ri is the location of the ith point charge qi If the ith point charge qi is implemented as a sphere with radius Ri and a uniform charge distribution at potential Ri, Equation (1) can be rewritten as:

N

E(r ) = ∑ Vi Ri i =1

r − ri r − ri

3

(2)

Mathematical Model Equation of Motion of a Charged Particle

A particle of charge Q, velocity v and rest mass m0 in combined static electric and magnetic fields, is:

QE(r ) + Qv × B(r ) = p& d = (γ m0 v ) dt v ⋅ v& ⎞ ⎛ = γ m0 ⎜ v&+ γ 2 2 v ⎟ c ⎝ ⎠ where, γ ≡ (1 − v 2 / c 2 )

−1 / 2

(3)

Mathematical Model Solution to Particle Equation of Motion The acceleration of the particle, a ≡ v&, of the particle is calculated by re-writing Equation (3):

Q C⋅a = (E(r ) + v × B(r ) ) γ m0 where,

⎛ c11 c12 ⎜ C = ⎜ c21 c22 ⎜c ⎝ 31 c32

2 ⎛ 2 vx ⎜1 + γ 2 c c13 ⎞ ⎜ ⎟ ⎜ 2 v y vx c23 ⎟ = ⎜ γ 2 c ⎟ c33 ⎠ ⎜ ⎜ γ 2 vz vx 2 ⎜ c ⎝

γ

2

vx v y

1+ γ

γ2

c2 2 v y 2 2

c vz v y c2

(4)

⎞ ⎟ ⎟ ⎟ 2 γ ⎟ c2 ⎟ 2 2 vz ⎟ 1+ γ 2 ⎟ c ⎠

γ2

vx vz c2 v y vz

(5)

Mathematical Model Solution to Particle Equation of Motion Solving for a in Equation (4),

a=

Q −1 C ⋅ (E(r ) + v × B(r ) ) γ m0

⎛ Ax ⎞ 1 ⎜ ⎟ = ⎜ Ay ⎟ A0 ⎜ ⎟ ⎝ Az ⎠

(6)

where,

A0 = (c13c22c31 − c12c23c31 − c13c21c32 + c11c23c32 + c12c21c33 − c11c22c33 ) m0γ

Ax = (c23c32 Ex − c22c33 Fx − c13c32 Fy + c12c33 Fy + c13c22 Fz − c12c23 Fz ) Q

Ay = (− c23c31Fx + c21c33 Fx + c13c31Fy − c11c33 Fy − c13c21Fz + c11c23 Fz ) Q Az = (c22c31Fx − c21c32 Fx − c12c31Fy + c11c32 Fy + c12c21Fz − c11c22 Fz ) Q Fx ≡ E x + v y Bz − vz B y Fy ≡ E y + vz Bx − v x Bz Fz ≡ E z + vx B y − v y Bx

(7) (8a) (8b) (8c) (8d) (8e) (8f)

Mathematical Model Trajectory Difference Equations of Particle Motion Based on a Taylor series expansion about time point k, a set of difference equations for position and velocity can be expressed as:

v k +1 ≈ v k + v&k ∆t

(9a)

≈ v k + a k ∆t 2 rk +1 ≈ rk + r&k ∆t + 12 & r& k ∆t

≈ rk + v k ∆t + 12 a k ∆t where ∆t a constant time step.

(9b) 2

Mathematical Model Magnetic Field due to a Current Loop The magnetic field from a single current loop is:

Bx ( x, y, z ) =

z i y

B y ( x, y , z ) =

a

((a

Cxz 2α βρ 2

2

2

)

(10a)

)

(10b)

+ R 2 ) E(k 2 ) − α 2 K(k 2 )

(

Cyz 2 2 2 2 2 ( a + R ) E( k ) − α K( k ) 2 2 2α βρ

x Circular Current Loop.

Bz ( x, y, z ) =

C 2α

2

( (a β

2

− R 2 ) E(k 2 ) + α 2 K(k 2 )

)

where E(k2) and K(k2) are the complete elliptic integrals of the first and second kind, respectively, and:

ρ 2 ≡ x2 + y2

α 2 ≡ a 2 + R 2 − 2 aρ

k 2 ≡ 1−α 2 / β 2

R2 ≡ ρ 2 + z2

β 2 ≡ a 2 + R 2 + 2 aρ

C ≡ µ0 i /π

(10c)

Mathematical Model Magnetic Field due to a Spherical Solenoid −1)

1 (M

(

)

(

)

M x −1 2 2 2 Cxz 2 z (amn + Rm2 ) E(kmn ) − α 2 K(kmn ) Bx ( x, y, z ) = ∑ ∑ 2 2 α mn β mn 2 ρ m = − 12 ( M z −1) n = 0 1 (M

−1)

M x −1 2 2 2 Cyz 2 z (amn + Rm2 ) E(kmn ) − α 2 K(kmn ) B y ( x, y , z ) = ∑ ∑ 2 α mn β mn 2 ρ 2 m = − 12 ( M z −1) n = 0

C Bz ( x, y, z ) = 2 .

1 (M z 2

−1)

∑

m = − 12 ( M z

M x −1

∑

((a

−1) n = 0

2 mn

2 2 − Rm2 ) E(kmn ) + α 2 K(kmn ) 2 α mn β mn

)

(11a)

(11b)

(11c)

where E(k2) and K(k2) are the complete elliptic integrals of the first and second kind, respectively, and: 2 2 2 2 2 α mn ≡ amn + Rm2 − 2amn ρ kmn ≡ 1 − α mn / β mn ρ 2 ≡ x2 + y2 Rm2 ≡ ρ 2 + ( z − md z )

2

2 2 β mn ≡ amn + Rm2 + 2amn ρ

amn ≡ nd x + a02 − (md z ) 2

The radius of each loop is: where,

md z < a0

and

C ≡ µ0 i /π

1 2

( M z − 1)d z < a0

(12)

Mathematical Model Initial Particle Velocity calculated from Initial Particle Energy Total energy of a particle of rest mass m0 is:

E = mc 2

(13a)

Total energy is the sum of rest mass energy and kinetic energy:

E = E0 + T

(13b)

= m0c + T 2

T = mc 2 − E0

Solve for T in term of v:

= γ m0c − m0c = (γ − 1)m0c 2

2

2

(13c)

where, γ ≡ (1 − v 2 / c 2 )

−1 / 2

m0c 2 Solve for v in term of T, with ξ ≡ : qT

v=

c 1 + 2ξ 1+ ξ

(13d)

Present Radiation Shielding Studies at KSC ASRC NASA (Spacecraft)

SoftwareMathematical Modeling

NIAC (Lunar) Analysis of a Lunar Base Electrostatic Radiation Shield Concept Phase I: NIAC CP 04-01 Advanced Aeronautical/Space Concept Studies Charles R. Buhler, Principal Investigator (321) 867-4861 October 1, 2004 ASRC Aerospace Corporation P.O. Box 21087 Kennedy Space Center, Florida 32815-0087

SoftwareMathematical Modeling

~ $1.9 M / 4 yrs

Field Precision, NM ~ $0.07 M / 6 mo

Problems already being addressed by NASA Shield Configuration and Design for spacecraft Shield Effectiveness Material Tensile Strength/Dielectric Strength Other Material Issues-Mechanical (Attachment, etc.)

Other Material Issues-Environmental (Temperature, UV resistance) Other Material Issues-Misc. (Leakage current, Gamma resistance, Thickness/Weight, Crease resistance, Conductive coating (CNT or CVD Au), Aging) Shield Forces Net Shield Charge Shield Discharge Calculations-Leakage, Corona, Plasma.

Charge Buildup on outside of Spheres.

Power Supply Feasibility-Voltage Power Supply Feasibility-Current Field Extent in a Plasma Particle Entrapment Safety-Total Stored Energy Safety-Shield Stability Safety-Electron Dosage Issue

Future Work required for a Lunar Solution • Lunar Shield configuration • Lunar gravity • Lunar surface may or may not act as a sufficient electrical ground. [Power systems may have the benefit of free charges that a spacecraft will not have access to.]

• Lunar Shield will have to contend with Lunar dust.

Proposed Validation Experiment Particle Detector Lunar Shield Model Under Test High Vacuum Chamber

P ∈ {10−5 ,10−10 } [torr]

Accelerator Grid

∆V ∈ {102 ,104 } [volts] Ion Selector

Ion Source

Broad-Band Energy Distribution to Simulate SPE Distribution