Overview. Objective Background Design Constraints User Requirements Alternatives Selected Concept Design Evaluation Plan

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Emmeline Sharyl Thornton
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2 Overview Objective Background Design Constraints User Requirements Alternatives Selected Concept Design Evaluation Plan

3 Objective To design the outer structure and material components of a lunar base to reduce radiation exposure to an annual dosage of 50 rems or less for astronauts occupying the moon for up to six months.

4 Types of Radiation Solar Energetic Particles (SEPs) composed of protons, electrons and heavy ions solar flares Galactic Cosmic Rays (GCRs) composed of protons, electrons, and atomic nuclei Radioactive Decay secondary and tertiary radiation emitted from the Moon s surface

5 Approx. Dose (REM) National Council for Radiation Protection Annual Limit of 50 REMs per year for astronauts Biological Effects Effect on Human Body 25 Detectable changes in blood < 100 No immediate harmful effects > st signs of radiation sickness >300 Damage to nerve cells and gastro tract, severe loss of white blood cells, reduced production blood platelets > 450 LD-50; fever and diarrhea > 800 Always fatal ( 2 to 14 days)

6 Design Constraints A temperature range from -50 ± 10 degrees Celsius Gravity that is 1.62 m/s 2 (1/6 the gravity of Earth) Radiation exposure of 30 to 100 rems per year Peary Crater is permanently lit by the Sun, light availability will not be a factor

7 User Requirements Radiation Reduction (50%) Impact Resistance (25%) Feasibility (15%) Weight (10%)

8 Summary of Alternatives Possible Alternatives 1. Aluminum currently in use by NASA 2. Liquid Hydrogen high electron density, excels at radiation protection 3. Lithium Hydride- lightweight compound used in nuclear reactors as radiation barrier 4. Regolith- readily available on Moon s surface 5. RXF1- structural polyethylene material

Alternative 1: Aluminum Alloys Design Constraint Material Rank Point Value Radiation Reduction 2 1 Impact Resistance 4 1 Technological Feasibility 6.9 Weight 1.2 TOTAL: 3.

9 Alternative 1: Aluminum Alloys Design Constraint Material Rank Point Value Radiation Reduction 2 1 Impact Resistance 4 1 Technological Feasibility 6.9 Weight 1.2 TOTAL: 3.1 Conventional Spacecraft Material Partially Effective against GCR (lower energy) HZE (higher energy) may produce secondary radiation Sustains meteorite impacts at speeds of km/s. [16]

Alternative 2: Liquid Hydrogen Ideal radiation shield Liquid Or Gaseous State contained in tank Present on the moon Hydrogen as propulsion and shield Tens of

10 Alternative 2: Liquid Hydrogen Ideal radiation shield Liquid Or Gaseous State contained in tank Present on the moon Hydrogen as propulsion and shield Tens of tons required Design Constraint Material Rank Point Value Radiation Reduction 6 3 Impact Resistance Technological Feasibility Weight TOTAL: 3.9

Alternative 3: Lithium Hydride Design Constraint Material Rank Point Value Radiation Reduction 4 2 Impact Resistance 3.75 Technological Feasibility 3.45 Weight 4.4 TOTAL: 3.

11 Alternative 3: Lithium Hydride Design Constraint Material Rank Point Value Radiation Reduction 4 2 Impact Resistance 3.75 Technological Feasibility 3.45 Weight 4.4 TOTAL: 3.6 Highest electron density of all hydrides Radiation dose equivalent graphs show it ranks only below liquid hydrogen and polyethylene Lightweight, density =.82 g/cc Safety hazard when combined with water

Alternative 4: Regolith Design Constraint Requires 1 to 2 meters of material for radiation and impact protection Readily available on the lunar surface Material Rank Transportation of machines

12 Alternative 4: Regolith Design Constraint Requires 1 to 2 meters of material for radiation and impact protection Readily available on the lunar surface Material Rank Transportation of machines to process is required Point Value Radiation Reduction Impact Resistance Technological Feasibility Weight TOTAL: 4.35 Image Source:

13 Alternative 5: RXF1 Brand new material in materials science. Structural polyethylene On a chemical level, ethylene is the major building block of RXF1 Comprised mostly of hydrogen and carbon atoms Hydrogen works best for Galactic Cosmic Rays (GCR) because it actually interacts with the charged particles Key attributes: 2.6 times lighter than aluminum Polyethylene, when compared to 5 g/cm 2 of aluminum: 50% better at shielding solar flares 15% better at shielding cosmic rays Starts out as a fabric so it can be draped around molds to be shaped in any form The density is equal to 1.11 g/cm 3

Alternative 5: RXF1 An areal density of 15 g/cm 2 could keep the dose equivalence at the annual limit of 50 csv/yr (or 50 rems/yr). 0.5 cm can stop a 1-mm cylinder traveling 7.

14 Alternative 5: RXF1 An areal density of 15 g/cm 2 could keep the dose equivalence at the annual limit of 50 csv/yr (or 50 rems/yr). 0.5 cm can stop a 1-mm cylinder traveling 7.2 km/sec Extremely light weight Design Constraint Material Rank Point Value Radiation Reduction Impact Resistance Technological Feasibility 3.45 Weight 3.3 TOTAL: 4.5

15 Alternative Comparison Radiation Reduction (0.50) Impact Resistance (0.25) Feasibility (0.15) Weight (0.1) Alternative Rank Points Rank Points Rank Points Rank Points Aluminum RXF Regolith LiH Hydrogen Figure 2: Alternative Criteria Ranking Data Alternative Final Score Final Rank Aluminum RXF Regolith LiH Hydrogen Figure 3: Final Alternative Rankings

16 Selected Concept Design RXF1 This is a sensible option considering the strength of this material and the amount of radiation protection that it offers Figure 1: Dose Equivalent vs. Areal Density

17 Selected Concept Design Figure 4: Lunar Module Shell Using the payload capacities of the Ares V rocket, the shape of the modules may resemble this. Material volume is close to 55m 3 Mass = 61, 050 kg 10,000 kg less than the payload capacity of Ares V to Trans Lunar Injection

18 Selected Concept Design Minimum thickness of RXF1 Areal Density = ρ * l ρ = average density l = average thickness Module Shown (Figure 4) Comprised of 8 inch thick walls Using Figure 1 15 g/cm 2 = (1.11g/cm 3 ) *l l = (15 g/cm 2 ) / (1.11g/cm 3 ) l = cm 5.32 in

19 Selected Concept Design Ideally, once the module is on the lunar surface, an astronaut would complete EVAs to cover the module with regolith This would provide: Another layer of radiation shielding Another layer of meteorite protection Insulation to reduce thermal variances Adding this layer of regolith would reduce the amount of radiation exposure level to an insignificant amount

20 Evaluation Plan Visit Marshall Space Flight Center and use their radiation software to run the necessary simulations based on our alternatives Determine the dose equivalents and evaluate our proposed solution If this is not authorized we will use web-based Geant 4 simulation software Build a physical mockup of our emergency SPE shelter using a lab on campus Monitor volunteers for a 12 to 24 hour period Measure subject s : comfort level mental stability ability to move ability to maintain sufficient production levels

21 References Eckart, Peter. The Lunar Base Handbook. Second ed. Boston: McGraw-Hill Companies, Print. "RXF1 Specs." Message to Raj Kaul. 1 Nov Britt, Robert R. "Perfect Spot Found for Moon Base." SPACE.com. 13 Apr Web. < Seybold, Calina C. "Characteristics of the Lunar Environment." Aug Web. 13 Oct < Lindsey, Nancy J. "Lunar Station Protection: Lunar Regolith Shielding." Web. <

22 References United States. NASA. Shielding Strategies for Human Space Exploration. Ed. J.W. Wilson, J. Miller, F.A. Cucinotta, and A. Konradi. NASA Conference Publication, Print. Adams, J.H., T.A. Parnell, D.H. Hathaway, J.C. Gregory, and R.N. Grugel. United States. Revolutionary Concepts of Radiation Shielding for Human. Huntsville: The University of Alabama in Huntsville, (Adams, Parnell, Hathaway, Gregory, and Grugel) Nealy, John E., John W. Wilson, and Larence W. Townsend. United States. Solar-Flare Shielding With Regolith at a Lunar-Base Site. Hampton, VA: Print. Nealy, John E., and Lisa C. Simonson. United States. Radiation Protection for Human Missions to the Moon and Mars. Washington D.C.: Print.

23 Beyond Questions

Geant4 Based Space Radiation Application for Planar and Spherical Geometries

Geant4 Based Space Radiation Application for Planar and Spherical Geometries Advances in Applied Sciences 2017; 2(6): 110-114 http://www.sciencepublishinggroup.com/j/aas doi: 10.11648/j.aas.20170206.13 ISSN: 2575-2065 (Print); ISSN: 2575-1514 (Online) Geant4 Based Space Radiation