Radiation Physiology and Effects • Sources and types of space radiation! • Effects of radiation! • Shielding approaches! • Recent advances in understanding of radiation and its affects

© 2015 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 1 ENAE 697 - Space Human Factors and Life Support The Origin of a Class X1

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 2 ENAE 697 - Space Human Factors and Life Support The Earth’s Magnetic Field

Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 3 ENAE 697 - Space Human Factors and Life Support The Van Allen Radiation Belts

Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 4 ENAE 697 - Space Human Factors and Life Support Cross-section of Van Allen Radiation Belts

Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 5 ENAE 697 - Space Human Factors and Life Support Flux in Low Earth Orbit

Ref: V. L. Pisacane and R. C. Moore, Fundamentals of Space Systems Oxford University Press, 1994

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 6 ENAE 697 - Space Human Factors and Life Support Heavy Flux

Background Solar Flare Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 7 ENAE 697 - Space Human Factors and Life Support Radiation Units • Dose D= absorbed radiation! ! Joule ergs 1 Gray =1 = 100 rad = 10, 000 ! kg gm • Dose equivalent H= effective absorbed radiation! ! Joule ergs 1! Sievert =1 = 100 rem = 10, 000 kg gm ! ! H = DQ rem = RBE rad • LET = Linear Transfer

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 8 ENAE 697 - Space Human Factors and Life Support Radiation Quality Factor

Radiation Q X-rays 1 5 MeV γ-rays 0.5 1 MeV γ-rays 0.7 200 KeV γ-rays 1 1 2-10 Neutrons 2-10 α-particles 10-20 GCR 20+ U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 9 ENAE 697 - Space Human Factors and Life Support Radiation in Free Space

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 10 ENAE 697 - Space Human Factors and Life Support Radiation Dose vs. Orbital Altitude

300 mil (7.6 mm) Al shielding Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 11 ENAE 697 - Space Human Factors and Life Support Dosage Rates from Oct/Nov 2003 SPE

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 12 ENAE 697 - Space Human Factors and Life Support SPEs in Solar Cycles 19, 20, and 21

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 13 ENAE 697 - Space Human Factors and Life Support GCR Constituent Species

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 14 ENAE 697 - Space Human Factors and Life Support Solar Max/Min GCR Flux Ratio

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 15 ENAE 697 - Space Human Factors and Life Support Radiation Damage to DNA

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 16 ENAE 697 - Space Human Factors and Life Support Symptomology of Acute Radiation Exposure • “Radiation sickness”: headache, dizziness, malaise, nausea, vomiting, diarrhea, lowered RBC and WBC counts, irritability, insomnia! • 50 rem (0.5 Sv)! – Mild symptoms, mostly on first day! – ~100% survival! • 100-200 rem (1-2 Sv)! – Increase in severity and duration! – 70% incidence of vomiting at 200 rem! – 25%-35% drop in blood cell production! – Mild bleeding, fever, and infection in 4-5 weeks

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 17 ENAE 697 - Space Human Factors and Life Support Symptomology of Acute Radiation Exposure • 200-350 rem (2-3.5 Sv)! – Earlier and more severe symptoms! – Moderate bleeding, fever, infection, and diarrhea at 4-5 weeks! • 350-550 rem (3.5-5.5 Sv)! – Severe symptoms! – Severe and prolonged vomiting - electrolyte imbalances! – 50-90% mortality from damage to hematopoietic system if untreated

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 18 ENAE 697 - Space Human Factors and Life Support Symptomology of Acute Radiation Exposure • 550-750 rem (5.5-7.5 Sv)! – Severe vomiting and nausea on first day! – Total destruction of blood-forming organs! – Untreated survival time 2-3 weeks! • 750-1000 rem (7.5-10 Sv)! – Survival time ~2 weeks! – Severe nausea and vomiting over first three days! – 75% prostrate by end of first week! • 1000-2000 rem (10-20 Sv)! – Severe nausea and vomiting in 30 minutes! • 4500 rem (45 Sv)! – Survival time as short as 32 hrs - 100% in one week

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 19 ENAE 697 - Space Human Factors and Life Support Long-Term Effects of Radiation Exposure

• Radiation carcinogenesis! – Function of exposure, dosage, LET of radiation! • Radiation mutagenesis! – Mutations in offspring! – Mouse experiments show doubling in mutation rate at 15-30 rad (acute), 100 rad (chronic) exposures! • Radiation-induced cataracts! – Observed correlation at 200 rad (acute), 550 rad (chronic)! – Evidence of low onset (25 rad) at high LET

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 20 ENAE 697 - Space Human Factors and Life Support Radiation Carcinogenesis • Manifestations! – Myelocytic leukemia! – Cancer of breast, lung, thyroid, and bowel! • Latency in atomic bomb survivors! – Leukemia: mean 14 yrs, range 5-20 years! – All other cancers: mean 25 years! • Overall marginal cancer risk! – 70-165 deaths/million people/rem/year! – 100,000 people exposed to 10 rem (acute) -> 800 additional deaths (20,000 natural cancer deaths) - 4%

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 21 ENAE 697 - Space Human Factors and Life Support NASA Radiation Dose Limits

U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 22 ENAE 697 - Space Human Factors and Life Support Density of Common Shielding Materials 12

10

8

6

4

2

0

Water Gr/Ep Lead Acrylics Aluminum Polyethylene U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 23 ENAE 697 - Space Human Factors and Life Support Comparative Thickness of Shields (Al=1) 3

2

1

0

Water Gr/Ep Lead Acrylics Aluminum Polyethylene U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 24 ENAE 697 - Space Human Factors and Life Support Comparative Mass for Shielding (Al=1) 5

4

3

2

1

0

Water Gr/Ep Lead Acrylics Aluminum Polyethylene U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 25 ENAE 697 - Space Human Factors and Life Support Effective Dose Based on Shielding

Francis A. Cucinotta, Myung-Hee Y. Kim, and Lei Ren, Managing Lunar and Mars Mission Radiation Risks Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness NASA/TP-2005-213164, July, 2005 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 26 ENAE 697 - Space Human Factors and Life Support Shielding Materials Effect on GCR

–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 27 ENAE 697 - Space Human Factors and Life Support Lunar Regolith Shielding for SPE

–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 28 ENAE 697 - Space Human Factors and Life Support Mars Regolith Shielding Effectiveness

–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 29 ENAE 697 - Space Human Factors and Life Support Radiation Exposure Induced Deaths

Francis A. Cucinotta, Myung-Hee Y. Kim, and Lei Ren, Managing Lunar and Mars Mission Radiation Risks Part I: Cancer Risks, Uncertainties, and Shielding Effectiveness NASA/TP-2005-213164, July, 2005 U N I V E R S I T Y O F Radiation Physiology and Effects MARYLAND 30 ENAE 697 - Space Human Factors and Life Support National Aeronautics and Space Administration

! What’s New in Space Radiation Research for Exploration? ! Francis A. Cucinotta NASA, Lyndon B. Johnson Space Center ! Presented to Future In-Space Operations (FISO) May 18, 2011 1 National Aeronautics and Space Administration The Space Radiation Problem

Space radiation is comprised of high- energy protons and heavy (HZE’s) and secondary protons, neutrons, and heavy ions produced in shielding – Unique damage to biomolecules, cells, and tissues occurs from HZE ions – No human data to estimate risk – Expt. models must be applied or developed to estimate cancer, and other risks – Shielding has excessive costs and will not eliminate galactic cosmic rays (GCR) !

Single HZE ions in cells Single HZE ions in photo-emulsions And DNA breaks Leaving visible images 2 National Aeronautics and Space Administration Executive Summary

• Estimating space radiation risks carries large uncertainties that preclude setting exposure limits and evaluating many mitigation measures ! • NASA needs to close the knowledge gap on a broad-range of biological questions before radiation protection goals can be met for exploration ! • The Human Research Program (HRP), Space Radiation Program Element (SRP) led by JSC is committed to solving the space radiation problem for exploration

3 National Aeronautics and Space Administration Space Radiation Environments

• Galactic cosmic rays (GCR) penetrating 100 Fluence (F) Dose = F x LET protons and heavy nuclei - a biological Dose Eq = Dose x QF science challenge 10 n o

t i 1 – shielding is not effective u b i t r

– large biological uncertainties limits ability to n o 0.1 evaluate risks and effectiveness of C %

mitigations 0.01 ! 0.001 0 5 10 15 20 25 30 • Solar Particle Events (SPE) largely medium GCR Charge Number energy protons – a shielding, operational, and risk assessment challenge GCR a continuum of types – shielding is effective; optimization needed to reduce weight – improved understanding of radiobiology needed to perform optimization – accurate event alert and responses is essential for crew safety

Solar particle events and the 11-yr solar cycle4 National Aeronautics and Space Administration Space Safety Requirements

• Congress has chartered the National Council on Radiation Protection (NCRP) to guide Federal agencies on radiation limits and procedures – NCRP guides NASA on astronaut dose limits • Crew safety – limit of 3% fatal cancer risk Cell fusion caused by radiation – prevent radiation sickness during mission

– new exploration requirements limit brain Sham TGFβ and heart disease risks from space radiation • Mission and Vehicle Requirements γ γ +TGFβ – shielding, dosimetry, and countermeasures • NASA programs must follow the ALARA Fe Fe+TGFβ principle to ensure astronauts do not approach dose limits Space Radiation in breast cancer formation 5 National Aeronautics and Space Administration Categories of Radiation Risk

Four categories of risk of concern to NASA: – Carcinogenesis (morbidity and mortality risk) – Acute and Late Central Nervous System (CNS) risks ✓ immediate or late functional changes cataractsLens changes in cataracts – Chronic & Degenerative Tissue Risks ✓ cataracts, heart-disease, etc. – Acute Radiation Risks – sickness or death Differences in biological damage of heavy nuclei in space with x-rays, limits Earth-based data on health effects for space applications – New knowledge on risks must be obtained

6 First experiments for leukemia induction with GCR National Aeronautics and Space Administration Space Radiation Health Risks

• NASA limits acceptable levels of risks of astronauts to a 3% Risk of Exposure Induced Death (REID) from cancer – PEL requirement to be below 95% Confidence Interval (C.I.) for cancer risk protects against uncertainties in risk projection models – Estimates of number of days to be within a 95% C.I. are used to assess: • Safe mission lengths • Crew selection criteria such as Age, Gender and Prior Exposure ! • Mitigations such as Shielding or Biological Countermeasure Requirements • Non-cancer risks are not well defined – Potential for late non-cancer mortality risks (Heart and CNS) on long- term exploration missions confounds assessments of Acceptable Risk, which includes only cancer at this time – Additionally, the NCRP recommends that limits for non-cancer morbidity risks be based on avoiding any clinically significant effect • Research in cells and murine models are not conclusive regarding clinical significance of space radiation exposure to the astronaut's CNS • Need appropriate animal model to assess clinical significance

7 CNS Risks from Galactic Cosmic Rays (GCR)

• Retinal flashes observed by astronauts suggests single heavy nuclei can disrupt brain function. ― Central nervous system (CNS) damage by x- rays is not observed except at very high doses • In-flight cognitive changes and late effects similar to Alzheimer’s disease are a concern for GCR. • NASA research in cells and mouse/rat models has increased concern for CNS Risks Reduction in number of neurons (neurodegeneration) for – Over 90 CNS journal publications supported increasing doses in mouse hippocampus by NASA since 2000 – Studies have quantified rate of neuronal degeneration, oxidative stress, apoptosis, inflammation, and changes in dopamine function related to late CNS risks – Cognitive tests in rats/mice show detriments at doses as low as 10 mGy (1 rad) • Large hurdle remains to establish significance in humans National Aeronautics and Space Administration Radiation and Non-Cancer Effects

Vasculature Damage by GCR • Early Acute risks are very unlikely: – Low or modest dose-rates for SPE’s insufficient Control Iron Nuclei for risk of early death – SPE doses are greatly reduced by tissue or vehicle shielding • Radiation induced Late Non-Cancer risks are well known at high doses and recently a concern at doses below 1 Sv (100 rem) – Significant Heart disease in Japanese Survivors and several patient and Reactor Worker Studies – Dose threshold is possible making risk unlikely for ISS Missions(<0.2 Sv) ; however a concern for Mars or lunar missions due to higher GCR and SPE dose – Qualitative differences between GCR and gamma-rays are a major concern

9 National Aeronautics and Space Administration NASA Space Radiation Laboratory

• A $34-million facility, is located at DOE’s Brookhaven National Laboratory is managed by NASA’s Johnson Space Center. It is one of the few places in the world that can simulate heavy ions in space. • New joint DoE-NASA Electron beam injector source (EBIS) for 2009 increases space simulation capability • $9 M Annual operations cost EBIS SC solenoid Beam port

Dipoles – preparing

RFQ Linac EBIS Construction National Aeronautics and Space Administration Major Sources of Uncertainty

• Radiation quality effects on biological damage – Qualitative and quantitative differences between space radiation compared to x- rays or gamma-rays • Dependence of risk on dose-rates in space – Biology of repair, cell & tissue regulation Durante & Cucinotta, Nature Rev. Cancer (2008) • Predicting solar events

0.015 – Temporal and size predictions Distribution aluminum Distribution polyethylene 0.012 Distribution Liq. (H2) • E(alum) = 0.87 Sv Extrapolation from experimental data to E(poly) = 0.77 Sv

E(H2) = 0.43 Sv R(alum) = 3.2 [1.0,10.5] (%) t y

i 0.009 l R(poly) = 2.9 [0.94, 9.2] (%)

humans i R(H2) = 1.6 [0.52, 5.1] (%) b a b

o 0.006

• Individual radiation-sensitivity r P

– Genetic, dietary and “healthy worker” 0.003 effects 0.000 0 3 6 9 12 15 (%) Fatal Cancer Risk Cucinotta et al Radiat Meas (2006) 1 1 Space Radiation Shielding is Well Understood

• NASA has invested in shielding technologies for many years and understanding is nearly complete Radiation Shielding Materials – Over 1,000 research publications since 1980 – 10000 Solar events can be shielded GCR L. Hydrogen – GCR requires enormous mass to shield GCR Polyethylene

r GCR Graphite because of high and secondary GCR Aluminum radiation / y GCR Regolith m 1000 SPE Graphite

e SPE Regolith • Highly accurate predictive codes exist SPE L. Hydrogen t , r

with +15% errors for organ exposure n e l 100

projections a v – Transport codes i u

– Environmental models q

– Optimal materials E 10 e

– Topology Design methods s o

• Knowledge missing is accurate D understanding of radiobiology for 1 Exposure to Risk conversion 0 5 10 15 20 25 30 35 Shielding Depth, g/cm2

August 1972 SPE and GCR Solar Min

12 Value Of Uncertainty Reduction Research: Cost of research to reduce uncertainties much less Confidence Levels for Career Risks on ISS than cost of shielding in space or reducing mission lengthEXAMPLE: 45-yr.-Old Males; GCR and trapped proton exposures

Current Uncertainties With Uncertainty Reduction 100 SAFE ZONE t i Solar Max

m Solar Max t o 90 i

l

e r c e n e e r 80 a d i c f

n w

o 70 o l C Solar Min e ) b 60 Solar Min ( % e b

50 0 250 500 750 1000 250 500 750 1000 Days on ISS Days on ISS National Aeronautics and Space Administration What’s New in Space Radiation Research?

• New Epidemiology data suggests much weaker age dependence on radiation cancer risks – Number 1 Trade variable (Astronaut age) is negated • Probabilistic risk assessments replace “rads and rem” – New Quality factors and uncertainty assessments • Galactic cosmic rays (GCR) are much higher concern than Solar particle events – Shielding plays only a small role for GCR • New health risks of concern from radiation – Heart disease, and Central nervous system (CNS) risks • Risks estimated to be much smaller for “Never-smokers”

14 National Aeronautics and Space Administration

Roles of Select Committees and Radiation Projection Councils

• Select expert panels from the National Academy of Sciences (NAS) and United Nations (UN) update human radio-epidemiology based estimates of radiation cancer risks each decade • These reports form the basis for revised radiation protection standards and policy as recommended by the US National Council on Radiation Protection and Measurements (NCRP) and International Commission on Radiological Protection (ICRP) • The most recent reports from NAS (BEIR VII) and the UN (UNSCEAR 2006) make important changes to the description of the age dependence of cancer risks, and cancer risks at low dose-rates – BEIR VII: Linear dose response with no age at exposure dependence above age 30-yr – UNSCEAR model shows similar age dependence for cancer incidence • These changes will increase risk projections if accepted by NASA

15 National Aeronautics and Space Administration NASA 2010 Cancer Projection Model

• NASA is developing new approaches to radiation risk assessment: – Probabilistic risk assessment framework – Tissue specific estimates • Research focus is on uncertainty reduction – Smaller tolerances are needed as risk increases, with <50% uncertainty required for Mars mission • NASA 2010 Model – Updates to Low LET Risk coefficients – Risks for Never-Smokers – Track Structure and Fluence based approach to radiation quality factors • Leukemia Q lower than Solid cancer Q GCR doses on Mars 1 6 National Aeronautics and Space Administration Radiation Risks for Never-Smokers

• More than 90% of Astronauts are never- Lung cancer in Unexposed smokers and remainder are former smokers • Smoking effects on Risk projections: – Epidemiology data confounded by possible radiation-smoking interactions, and errors documenting tobacco use – Average U.S. Population used by NCRP Reports 98 and 132 • NASA Model projects a 20 to 40-% risk reduction for never-smokers compared to U.S. Ave. – Larger decreases are possible if more were known on Risk Transfer models Thun et al., PLoS Med (2008) – Balance between Small Cell and Non-Small Cell Lung Cancer a critical question including high LET effects

1 7 National Aeronautics and Space Administration CDC Estimates of Smoking Attributable Cancers

Relative Risk to Never-smokers (NS) RR for NS to U.S. Avg

Males Current smokers Former smokers Never-smokers RR(NS/U.S.)

Esophagus 6.76 4.46 1 0.27 Stomach 1.96 1.47 1 0.71 Bladder 3.27 2.09 1 0.50 Oral Cavity 10.89 3.4 1 0.23 Lung* 23.26 8.7 1 0.11 Females Current smokers Former smokers Never-smokers RR(NS/U.S.)

Esophagus 7.75 2.79 1 0.35 Stomach 1.36 1.32 1 0.85 Bladder 2.22 1.89 1 0.65 Oral Cavity 5.08 2.29 1 0.46 Lung* 12.69 4.53 1 0.23

*Other cancers being considered Colon, leukemia, and liver National Aeronautics and Space Administration Point Estimates: Risk of Exposure Induced Death (REID) %REID per Sv

1 9 National Aeronautics and Space Administration

Fatal lung cancer risks per Sv (per 100 rem) Transfer model impact much larger change than >100 cm of GCR shielding– the 100 Billion Dollar question?

% REID, Females % REID, Males Age at Exposure 35, y 45, y 55, y 35, y 45, y 55, y

Model Type Model rates Average U.S. Population, 2005 Additive BEIR VII 1.20 1.20 1.18 0.65 0.66 0.66 UNSCEAR 1.28 1.27 1.22 0.71 0.71 0.69 RERF 1.33 1.34 1.32 0.72 0.73 0.73 Multiplicative BEIR VII 2.88 2.74 2.38 0.95 0.92 0.83 UNSCEAR 3.56 3.50 3.23 1.17 1.17 1.11 RERF 3.71 4.16 4.21 1.13 1.30 1.37 Mixture BEIR VII 2.04 1.97 2.78 0.80 0.79 0.74 UNSCEAR 2.43 2.39 2.23 0.94 0.94 0.89 RERF 2.53 2.77 2.78 0.92 1.02 1.05 Never-smokers Multiplicative BEIR VII 0.44 0.41 0.37 0.15 0.15 0.14 UNSCEAR 0.57 0.57 0.54 0.15 0.15 0.14 RERF 0.55 0.61 0.66 0.14 0.15 0.16 Mixture BEIR VII 0.85 0.84 0.81 0.40 0.40 0.38 UNSCEAR 0.96 0.95 0.91 0.46 0.45 0.42 RERF 0.98 1.01 1.02 0.46 0.47 0.45 Generalized RERF, Generalized 0.39 0.47 0.53 0.16 0.17 0.20 Multiplicative Multiplicative for never-smokers National Aeronautics and Space Administration “Safe” days in Space: Uncertainties estimated using subjective PDFs propagated using Monte-Carlo techniques

%REID predictions and 95% CI for never-smokers and average U.S. population for 1-year in deep space at solar minimum with 20 g/cm2 aluminum shielding: %REID for Males and 95% CI %REID for Females and 95% CI a Avg. U.S. Never-Smokers Decrease Avg. U.S. Never-Smokers Decrease (%) (%) 30 2.26 [0.76, 8.11] 1.79 [0.60, 6.42] 21 3.58 [1.15, 12.9] 2.52 [0.81, 9.06] 30 40 2.10 [0.71, 7.33] 1.63 [0.55, 5.69] 22 3.23 [1.03, 11.5] 2.18 [0.70, 7.66] 33 50 1.93 [0.65, 6.75] 1.46 [0.49, 5.11] 24 2.89 [0.88, 10.2] 1.89 [0.60, 6.70] 34

Maximum Days in Deep Space with 95% Confidence to be below Limits (alternative quality factor errors in parenthesis): a NASA 2005 NASA 2010 NASA 2010 Avg. U.S. Never-Smokers Males 35 158 140 (186) 180 (239) 45 207 150 (200) 198 (263) 55 302 169 (218) 229 (297) Females 35 129 88 (120) 130 (172) 45 173 97 (129) 150 (196) 55 259 113 (149) 177 (231) Solar Min and Max Comparison with Proposed NASA Quality Factor (Q) and Tissue Weights (Wt) vs ICRP Quality Factor Definition

22 National Aeronautics and Space Administration Shielding Materials play little role for GCR E (Sv) Material SPE + Solar Solar Minimum Maximum

Liquid H2 0.40 0.19

Liquid CH4 0.50 0.30 Polyethylene 0.52 0.33 10 g/cm2 Water 0.53 0.35 Epoxy 0.53 0.36 Aluminum 0.57 0.43

Liquid H2 0.36 0.16

Liquid CH4 0.45 0.22 Polyethylene 0.47 0.24 20 g/cm2 Water 0.48 0.25 Epoxy 0.49 0.26 Aluminum 0.53 0.30

Liquid H2 0.31 0.15

Liquid CH4 0.43 0.21 Polyethylene 0.46 0.23 40 g/cm2 Water 0.46 0.23 Epoxy 0.48 0.24 Aluminum 0.51 0.26 Annual effective dose. Solar max calculations include 1972 Solar Particle Event. 23 National Aeronautics and Space Administration

Solar Particle Event (SPE) Risks

Research studies show that risks of acute death from large SPEs has been over- estimated in the past: – Proper evaluation of dose-rates, tissue shielding, and proton biological effectiveness show risk is very small SPE risk remain important for lunar EVA – Radiation sickness if unprotected > 2 hour EVA – Cancer risk is priority for both EVA and IVA Proper resource management through research: – Probabilistic risk assessment tools for Lunar and Mars Architecture studies – Optimize shielding requirements by improved understanding of proton radiobiology & shielding design tools – ESMD and SMD collaborations on research to improve SPE alert, monitoring and forecasting – Biological countermeasure development for proton cancer, and Acute radiation syndromes (if needed)

24 National Aeronautics and Space Administration SPE Probabilistic Risk Assessment

SPE Hazard Rate in Space Era • Using detailed data base of all SPE’s in 160 space age (1955-current) and historical 140 data on Ice-core nitrate samples (15th- 120 century to current), SRP has developed 100

( t ) 80 a probabilistic model of SPE occurrence, λ size, and frequency 60 – Hazard rate model using Survival 40 analysis 20

0 – 2/1/54 2/1/58 2/1/62 2/1/66 2/1/70 2/1/74 2/1/78 2/1/82 2/1/86 2/1/90 2/1/94 2/1/98 2/1/02 2/1/06 Non-uniform Poisson process Date provides high quality fit of all SPE data Non-Uniform Poisson Process • Probabilistic model supports shielding 1

design and resource management goals 0.8 for Exploration missions

0.6

• Department of Defense model Model P Sample

estimates various acute risks 0.4

0.2

0 25 0 500 1000 1500 2000 2500 3000 3500 4000 Time, d National Aeronautics and Space Administration

Acceptable Risk Levels for Exploration Missions

• The NASA Standard of 3% Risk of Exposure Induced Death was set in 1989 by NASA Administrator with OSHA Concurrence under Code of Federal Regulation (CFR 1960) • NASA has set an identical acceptable risk level for Exploration missions under the OCHMO’s 2006 Permissible Exposure Limits (PEL) – OSHA concurrences on NASA Health policy in Spaceflight dropped in 2004 after discussion with OCHMO • The NCRP recommendation of 3% Limit based on 3 rationales: – Comparison of fatality rates in less-safe Industries made in 1989 – Comparison to risk limits for ground-based workers – Recognition of other spaceflight risks • Fatality rates in less-safe industries have improved more than 2-fold since 1989 and therefore no longer valid basis; however other 2 rationale from NCRP in 1989 are still valid

26 National Aeronautics and Space Administration

Acceptable Levels of Risk - continued

• A discussion of higher or lower Acceptable Risk Levels would consider – Over arching Ethical and Safety standards at NASA and in the U.S. – Benefits to Human-kind from Exploration missions – Emerging information on possible radiation mortality risks from non- cancer diseases, notably Heart (Stroke and Coronary Heart Disease) and Central Nervous System risks – The resulting burden for morbidity risks including cancer, cataracts, aging, and other diseases that entail pain, suffering, and economic impacts • Radiation cancer incidence probability approximately Two times higher than cancer death probability – Improvements in other areas of safety at NASA, other government agencies and work places since 1989 – Balance between other space flight risks and space radiation risks • NCRP Recommendation is the high risk nature of space missions precludes allowing an overly large radiation risk to Astronauts – Impacts on finding solutions through research programs and mission design architectures that result from Acceptable Risk Standards

27 National Aeronautics and Space Administration 3% and 6% Cancer Mortality Risks at 90% to 95% Confidence Levels (CL) (Solar Min at 20 g/cm2 Aluminum) Number of Days in Deep Space At Solar minimum with a 95% or 90% CL to be below 3% or 6% Risk of Cancer Death from Space Radiation (Avg US pop) 3% Risk 6% Risk (REID) (REID) 95% CL 90% CL 95% CL 90% CL Age, y Males 35 140 184 290 361 45 150 196 311 392 55 169 219 349 439 Age, y Females 35 88 116 187 232 45 97 128 206 255 55 113 146 234 293

28