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Radiation Physiology and EffectsENAE 697 - Space Human Factors and Life Support

U N I V E R S I T Y O FMARYLAND

Radiation Physiology and Effects• Sources and types of space radiation• Effects of radiation• Shielding approaches

1

© 2011 David L. Akin - All rights reservedhttp://spacecraft.ssl.umd.edu

http://spacecraft.ssl.umd.edu

http://spacecraft.ssl.umd.edu



The Origin of a Class X1 Solar Flare

2



The Earth’s Magnetic Field

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

3



The Van Allen Radiation Belts


4



Cross-section of Van Allen Radiation Belts


5



Electron Flux in Low Earth Orbit


6



Heavy Ion Flux

Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999

Background Solar Flare

7



Radiation Units• Dose D= absorbed radiation

• Dose equivalent H= effective absorbed radiation

• LET = Linear Energy Transfer <KeV/µ m>

8

1 Gray = 1Joule

kg= 100 rad = 10, 000

ergs

gm

1 Sievert = 1Joule

kg= 100 rem = 10, 000

ergs

gm

H = DQ rem = RBE × rad



Radiation Quality Factor

9

Radiation QX-rays 1

5 MeV γ-rays 0.51 MeV γ-rays 0.7

200 KeV γ-rays 1.0Electrons 1.0Protons 2-10

Neutrons 2-10α-particles 10-20

GCR 20+



Radiation in Free Space

10



Radiation Dose vs. Orbital Altitude

Ref: Neville J. Barter, ed., TRW Space Data, TRW Space and Electronics Group, 1999

300 mil (7.6 mm) Al shielding

11



Dosage Rates from Oct/Nov 2003 SPE

12



SPEs in Solar Cycles 19, 20, and 21

13



GCR Constituent Species

14



Solar Max/Min GCR Proton Flux Ratio

15



Radiation Damage to DNA

16



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

17



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

18



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

19



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

20



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%

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NASA Radiation Dose Limits

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Density of Common Shielding Materials

23

0

2

4

6

8

10

12

Polyethyle

neWate

rGr/E

p

Acrylic

s

AluminumLea

d



Comparative Thickness of Shields (Al=1)

24

0

1

2

3

Polyethyle

neWate

rGr/E

p

Acrylic

s

AluminumLea

d



Comparative Mass for Shielding (Al=1)

25

0

1

2

3

4

5

Polyeth

ylene

Water

Gr/Ep

Acrylics

Aluminu

mLe

ad



Effective Dose Based on Shielding

26

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



Shielding Materials Effect on GCR

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–, Human Integration Design Handbook, NASA SP-2010-3407, Jan. 2010



Lunar Regolith Shielding for SPE

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Mars Regolith Shielding Effectiveness

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Radiation Exposure Induced Deaths

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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

Na#onal Aeronau#cs and Space Administra#on

1

What’s New in Space Radia#on

Research for Explora#on?

Francis A. Cucino.a

NASA, Lyndon B. Johnson Space Center

Presented to Future In-‐Space Opera#ons (FISO) May 18, 2011

2

The Space RadiaBon Problem

Space radia#on is comprised of high-‐energy protons and heavy ions (HZE’s) and secondary protons, neutrons, and heavy ions produced in shielding –  Unique damage to

biomolecules, cells, and Bssues occurs from HZE ions

–  No human data to esBmate risk –  Expt. models must be applied

or developed to esBmate cancer, and other risks

–  Shielding has excessive costs and will not eliminate galacBc cosmic rays (GCR)

Single HZE ions in cells And DNA breaks

Single HZE ions in photo-‐emulsions Leaving visible images



3

ExecuBve Summary

•  EsBmaBng space radiaBon risks carries large uncertainBes that preclude seUng exposure limits and evaluaBng many miBgaBon measures

•  NASA needs to close the knowledge gap on a broad-‐range of biological quesBons before radiaBon protecBon goals can be met for exploraBon

•  The Human Research Program (HRP), Space RadiaBon Program Element (SRP) led by JSC is commi.ed to solving the space radiaBon problem for exploraBon


Space RadiaBon Environments

•  Galac#c cosmic rays (GCR) penetra#ng protons and heavy nuclei -‐ a biological science challenge –  shielding is not effec#ve –  large biological uncertain#es limits ability

to evaluate risks and effec#veness of mi#ga#ons

•  Solar Par#cle Events (SPE) largely medium

energy protons – a shielding, opera#onal, and risk assessment challenge –  shielding is effec#ve; op#miza#on needed

to reduce weight –  improved understanding of radiobiology

needed to perform op#miza#on –  accurate event alert and responses is

essen#al for crew safety

4

GCR a conAnuum of ionizing radiaAon types

Solar parAcle events and the 11-‐yr solar cycle

GCR Charge Number0 5 10 15 20 25 30

% C

ontr

ibut

ion

0.001

0.01

0.1

1

10

100Fluence (F)Dose = F x LETDose Eq = Dose x QF


5

Space Safety Requirements

•  Congress has chartered the Na#onal Council on Radia#on Protec#on (NCRP) to guide Federal agencies on radia#on limits and procedures

–  NCRP guides NASA on astronaut dose limits

•  Crew safety –  limit of 3% fatal cancer risk –  prevent radia#on sickness during mission –  new explora#on requirements limit brain

and heart disease risks from space radia#on

• Mission and Vehicle Requirements –  shielding, dosimetry, and

countermeasures • NASA programs must follow the ALARA principle to ensure astronauts do not approach dose limits

Cell fusion caused by radiaAon

Fe+TGFβ

γ

TGFβ

Fe

γ +TGFβ

Sham

Space RadiaAon in breast cancer formaAon


6

Categories of RadiaBon 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 func#onal changes

–  Chronic & Degenera>ve Tissue Risks

 cataracts, heart-‐disease, etc.

–  Acute Radia>on 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 applicaBons

–  New knowledge on risks must be obtained

Lens changes in cataracts

First experiments for leukemia inducAon with GCR

cataracts


Space RadiaBon 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 uncertain#es in risk projec#on models –  Es#mates of number of days to be within a 95% C.I. are used to assess:

•  Safe mission lengths •  Crew selec#on criteria such as Age, Gender and Prior Exposure •  Mi#ga#ons such as Shielding or Biological Countermeasure Requirements

•  Non-‐cancer risks are not well defined –  Poten#al for late non-‐cancer mortality risks (Heart and CNS) on long-‐

term explora#on missions confounds assessments of Acceptable Risk, which includes only cancer at this #me

–  Addi#onally, 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 radia#on exposure to the astronaut's CNS

•  Need appropriate animal model to assess clinical significance

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•  Re#nal flashes observed by astronauts suggests single heavy nuclei can disrupt brain func#on. ―  Central nervous system (CNS) damage by

x-‐rays is not observed except at very high doses

•  In-‐flight cogni#ve 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 –  Over 90 CNS journal publicaBons

supported by NASA since 2000 –  Studies have quanBfied rate of neuronal

degeneraBon, oxidaBve stress, apoptosis, inflammaBon, and changes in dopamine funcBon related to late CNS risks

–  CogniBve tests in rats/mice show detriments at doses as low as 10 mGy (1 rad)

•  Large hurdle remains to establish significance in humans

0

50

100

150

200

250

300

350

No.

Dcx

-pos

itive

Cel

ls

0 Gy 1 Gy 2 Gy 3 Gy

ReducBon in number of neurons (neurodegeneraBon) for increasing Iron doses in mouse hippocampus

CNS Risks from GalacBc Cosmic Rays (GCR)

Oxidative Stress (Lipid peroxidation:4Oxidative Stress (Lipid peroxidation:4--Hydroxynonenal) is Increased in Hydroxynonenal) is Increased in Mouse Hippocampus 9 Months After 2 GyMouse Hippocampus 9 Months After 2 Gy of of 5656Fe Fe IrradiationIrradiation

ControlControl Iron irradiatedIron irradiated


RadiaBon and Non-‐Cancer Effects

•  Early Acute risks are very unlikely: –  Low or modest dose-‐rates for SPE’s

insufficient for risk of early death –  SPE doses are greatly reduced by #ssue or

vehicle shielding •  Radia#on 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 pa#ent 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

–  Qualita#ve differences between GCR and gamma-‐rays are a major concern

9

Control Iron Nuclei Vasculature Damage by GCR

NASA Space RadiaBon Laboratory •  A $34-‐million facility, is located at DOE’s Brookhaven Na#onal 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 simula#on capability •  $9 M Annual opera#ons cost

Beam port

RFQ Linac

EBIS SC solenoid

Dipoles – preparing

EBIS Construc#on

NaBonal AeronauBcs and Space AdministraBon

11

Major Sources of Uncertainty Na#onal Aeronau#cs and Space Administra#on

•  Radia#on quality effects on biological damage – Qualita#ve and quan#ta#ve differences between space radia#on compared to x-‐rays or gamma-‐rays

•  Dependence of risk on dose-‐rates in space – Biology of repair, cell & #ssue regula#on

•  Predic#ng solar events – Temporal and size predic#ons

•  Extrapola#on from experimental data to humans

•  Individual radia#on-‐sensi#vity – Gene#c, dietary and “healthy worker” effects

Durante & Cucinora, Nature Rev. Cancer (2008)

(%) Fatal Cancer Risk0 3 6 9 12 15

Probab

ility

0.000

0.003

0.006

0.009

0.012

0.015

Distribution aluminumDistribution polyethyleneDistribution Liq. Hydrogen (H2) E(alum) = 0.87 Sv E(poly) = 0.77 SvE(H2) = 0.43 SvR(alum) = 3.2 [1.0,10.5] (%)R(poly) = 2.9 [0.94, 9.2] (%)R(H2) = 1.6 [0.52, 5.1] (%)

Cucinora et al Radiat Meas (2006)

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Space Radia#on Shielding is Well Understood

Radia#on Shielding Materials

August 1972 SPE and GCR Solar Min

Shielding Depth, g/cm20 5 10 15 20 25 30 35

Dose

Equ

ivalen

t, rem

/yr1

10

100

1000

10000GCR L. HydrogenGCR PolyethyleneGCR GraphiteGCR AluminumGCR RegolithSPE GraphiteSPE RegolithSPE L. Hydrogen

•  NASA has invested in shielding technologies for many years and understanding is nearly complete

–  Over 1,000 research publicaBons since 1980

–  Solar events can be shielded –  GCR requires enormous mass to shield

because of high energies and secondary radiaBon

•  Highly accurate predic#ve codes exist with +15% errors for organ exposure projec#ons

–  Transport codes –  Environmental models –  Op#mal materials –  Topology Design methods

•  Knowledge missing is accurate understanding of radiobiology for Exposure to Risk conversion

Confidence Levels for Career Risks on ISSEXAMPLE: 45-yr.-Old Males; GCR and trapped proton exposures

Solar Max

Days on ISS0

(%) C

onfid

ence

tobe

bel

ow c

aree

r lim

it

100Current Uncertainties With Uncertainty Reduction

50

60

70

80

90

250 500 750 1000 250 500 750 1000Days on ISS

Solar Max

Solar MinSolar Min

SAFE ZONE

Value Of Uncertainty Reduc#on Research: Cost of research to reduce uncertain#es much less than cost of shielding in space or reducing mission length


What’s New in Space RadiaBon Research?

•  New Epidemiology data suggests much weaker age dependence on radia#on cancer risks –  Number 1 Trade variable (Astronaut age) is negated

•  Probabilis#c risk assessments replace “rads and rem” –  New Quality factors and uncertainty assessments

•  Galac#c cosmic rays (GCR) are much higher concern than Solar par#cle events –  Shielding plays only a small role for GCR

•  New health risks of concern from radia#on –  Heart disease, and Central nervous system (CNS) risks

•  Risks es#mated to be much smaller for “Never-‐smokers”

14

Roles of Select Commi.ees and RadiaBon ProjecBon Councils

•  Select expert panels from the Na#onal Academy of Sciences (NAS) and United Na#ons (UN) update human radio-‐epidemiology based es#mates of radia#on cancer risks each decade

•  These reports form the basis for revised radia#on protec#on standards and policy as recommended by the US Na#onal Council on Radia#on Protec#on and Measurements (NCRP) and Interna#onal Commission on Radiological Protec#on (ICRP)

•  The most recent reports from NAS (BEIR VII) and the UN (UNSCEAR 2006) make important changes to the descrip#on 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 projec#ons if accepted by NASA

15



16

NASA 2010 Cancer ProjecBon Model

•  NASA is developing new approaches to radia#on risk assessment: –  Probabilis#c risk assessment framework

–  Tissue specific es#mates •  Research focus is on uncertainty

reduc#on –  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 radia#on quality factors

•  Leukemia Q lower than Solid cancer Q


GCR doses on Mars


RadiaBon Risks for Never-‐Smokers •  More than 90% of Astronauts are never-‐

smokers and remainder are former smokers

•  Smoking effects on Risk projec#ons: –  Epidemiology data confounded by possible

radia#on-‐smoking interac#ons, and errors documen#ng tobacco use

–  Average U.S. Popula#on used by NCRP Reports 98 and 132

•  NASA Model projects a 20 to 40-‐% risk reduc#on for never-‐smokers compared to U.S. Ave. –  Larger decreases are possible if more

were known on Risk Transfer models –  Balance between Small Cell and Non-‐Small

Cell Lung Cancer a cri#cal ques#on including high LET effects

17

Thun et al., PLoS Med (2008)

Lung cancer in Unexposed

CDC EsBmates of Smoking A.ributable Cancers

RelaBve 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

Point EsBmates: Risk of Exposure Induced Death (REID)

19

Na#onal Aeronau#cs and Space Administra#on %RE

ID per Sv

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 Multiplicative

RERF, Generalized Multiplicative for never-smokers

0.39 0.47 0.53 0.16 0.17 0.20


“Safe” days in Space: UncertainBes esBmated using subjecBve PDFs propagated using Monte-‐Carlo techniques

%REID for Males and 95% CI %REID for Females and 95% CI aE, y 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

aE, y NASA 2005 NASA 2010 Avg. U.S.

NASA 2010 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)

%REID predic#ons and 95% CI for never-‐smokers and average U.S. popula#on for 1-‐year in deep space at solar minimum with 20 g/cm2 aluminum shielding:

Maximum Days in Deep Space with 95% Confidence to be below Limits (alterna#ve quality factor errors in parenthesis):


Solar Min and Max Comparison with Proposed NASA Quality Factor (Q) and Tissue Weights (Wt) vs ICRP Quality Factor Defini#on

22

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120

E, mSv

x, g/cm2

Effective dose for Male behind Shielding

Annual GCR at Solar Minimum

Aluminum

Polyethylene

E(NASA Q)E(ICRP2007 Q/Wt)

Annual GCR at Solar MaximumAluminum

Polyethylene

E(NASA Q) E(ICRP2007 Q/Wt)

Shielding Materials play lirle role for GCR

23

Material E (Sv)

Solar Minimum SPE + Solar

Maximum

10 g/cm2

Liquid H2 0.40 0.19 Liquid CH4 0.50 0.30 Polyethylene 0.52 0.33 Water 0.53 0.35 Epoxy 0.53 0.36 Aluminum 0.57 0.43

20 g/cm2


40 g/cm2


Annual effective dose. Solar max calculations include 1972 Solar Particle Event.


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Solar ParBcle Event (SPE) Risks

NaBonal AeronauBcs and Space AdministraBon

Research studies show that risks of acute death from large SPEs has been over-‐esBmated in the past: – Proper evalua#on of dose-‐rates, #ssue shielding, and proton biological effec#veness show risk is very small

SPE risk remain important for lunar EVA – Radia#on sickness if unprotected > 2 hour EVA – Cancer risk is priority for both EVA and IVA

Proper resource management through research: – Probabilis#c risk assessment tools for Lunar and Mars Architecture studies – Op#mize shielding requirements by improved understanding of proton radiobiology & shielding design tools

– ESMD and SMD collabora#ons on research to improve SPE alert, monitoring and forecas#ng

– Biological countermeasure development for proton cancer, and Acute radia#on syndromes (if needed)


25

SPE ProbabilisBc Risk Assessment

•  Using detailed data base of all SPE’s in space age (1955-‐current) and historical data on Ice-‐core nitrate samples (15th-‐century to current), SRP has developed a probabilis#c model of SPE occurrence, size, and frequency –  Hazard rate model using Survival

analysis –  Non-‐uniform Poisson process

provides high quality fit of all SPE data

•  Probabilis#c model supports shielding design and resource management goals for Explora#on missions

•  Department of Defense model es#mates various acute risks

0

20

40

60

80

100

120

140

160

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

Date

λ (t)

SPE Hazard Rate in Space Era

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500 2000 2500 3000 3500 4000

Time, d

P ModelSample

Non-‐Uniform Poisson Process


Acceptable Risk Levels for ExploraBon 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 Regula#on (CFR 1960)

•  NASA has set an iden#cal acceptable risk level for Explora#on missions under the OCHMO’s 2006 Permissible Exposure Limits (PEL) –  OSHA concurrences on NASA Health policy in Spaceflight dropped in

2004 ayer discussion with OCHMO •  The NCRP recommenda#on of 3% Limit based on 3 ra#onales:

–  Comparison of fatality rates in less-‐safe Industries made in 1989 –  Comparison to risk limits for ground-‐based workers –  Recogni#on 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 ra#onale from NCRP in 1989 are s#ll valid

26


Acceptable Levels of Risk -‐ conBnued •  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 Explora#on missions –  Emerging informa#on on possible radia#on mortality risks from non-‐

cancer diseases, notably Heart (Stroke and Coronary Heart Disease) and Central Nervous System risks

–  The resul#ng burden for morbidity risks including cancer, cataracts, aging, and other diseases that entail pain, suffering, and economic impacts

•  Radia#on cancer incidence probability approximately Two #mes 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 radia#on risks •  NCRP Recommenda#on is the high risk nature of space missions precludes allowing an

overly large radia#on risk to Astronauts –  Impacts on finding solu#ons through research programs and mission

design architectures that result from Acceptable Risk Standards

27


28

3% Risk (REID)

6% Risk (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

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 Radia#on (Avg US pop)

3% and 6% Cancer Mortality Risks at 90% to 95% Confidence Levels (CL) (Solar Min at 20 g/cm2 Aluminum)

Page No. 1 Lora Bailey/10/31/2012

Johnson Space Center- Houston, Texas

Lora Bailey 10/31/2012

Engineering Directorate NASA Johnson Space Center

This package is for Deep Space Habitat Project

Pre-decisional Use Only

Future In-Space Operations (FISO) Telecon Colloquium

Deep Space Habitat Project

Radiation Studies for a

Long Duration Deep Space Transit Habitat



Presentation Purpose and Background

The purpose of this presentation is to show data and conclusions from radiation analysis conducted of Deep Space Habitat Project architectures

A new charter was initiated for the AES Deep Space Habitat Project at the beginning of FY2012 (October 2011)

Initiate development effort for a deep space transit habitat that would be manned for a minimum of 365 consecutive days, without crew changeout or provisioning resupply during that period Focus on the most pressing engineering challenges for a 1-year vehicle Include a launch packaging option that could utilize ELVs (in addition to SLS)

The Human Exploration Architecture roadmap showed the first deep space facility launching in 2019, to be manned by 2021

(* reference illustration below from D. Craig HEA charts dated January 3rd, 2012.)

2012 2013 2014 2015 2016 2017 2018 2019 2020 2021+

L2 Gateway Deployment L2 Gateway ISS Testing and Research L2 Test Flight OFT-1

?



*MSFC study/ ISS-Derived Deep Space Facility

*

D. Smitherman, et al, 12/2011.

Hab/Lab Module

Tunnel/Airlock

MPLM (Multi-Purpose Logistics Module)

This transit habitat consists of three basic elements:

1. an ISS Hab/Lab Module

2. a Tunnel/Airlock

3. an ISS MPLM

Orion

General Propulsion Module



*MSFC study/ ISS-Derived Deep Space Facility

*Reference chart

Configurations based

Smitherman, et al, 12/2011.

Habitation capability: 4 crewmembers

45.5 mtons



Existing ground ISS Assets*

Page 7

Raffaello MPLM FM2 at KSC SSPF

Node 1 STA at KSC SSPF

US Hab shell at MSFC Building 4755

* -Derived DSH

N1-STA, MPLM, and Hab modules



SE&I Architectural/Galactic Cosmic Radiation Analysis



Addressing GCR

Focus on GCR:

It can be viewed as the sound barrier we must break through to achieve real space exploration

Without addressing this challenge, we cannot conduct space travel and exploration for durations beyond our ~180-day limit, using architectures that employ reasonable risk-reduction methods

What we can do:

Embark on pursuing a best-effort solution that implements a smart architecture (beginning with use of current ISS elements), incorporates little/no additional dead mass shielding, and meets requirements in the middle as best possible



Radiation Primer, continued

SPE GCR

Occasional, infrequent events occurring most often during solar cycle maximum (~11-year cycles)

Monitoring of SPE radiation events is performed, and can be reported in a timely manner to the crew to seek shelter in a specified area containing shielding for short periods if deemed necessary

High flux but lower energy and are only for brief periods

Occurs all day every day, varying in flux with solar cycle (lower GCR levels occur during solar maximum)

Is omni-directional in addition to being continuous, so having a small designated area as a temporary shelter that contains shielding is not a solution option (also, outside LEO, magnetic field not present to help protect against GCR)

Moderate flux but much higher energy -- all day, every day

Definition comparison




SPE GCR

Shielding Effectiveness Comparison

SPE radiation is effectively curtailed by shielding. GCR radiation does not respond very favorably to shielding. Shielding has much less effectiveness against GCR.

~7% reduction ~50% reduction

Shielding is not conducive for

protecting against GCR.

, One-year dose , One-year dose for an idealized spherical model/shield for an idealized spherical model/shield



*

in one year

Effect of Solar Cycle on GCR Exposure



Permissible Exposure Limits (PEL), Stochastic Effects, and Risk of Exposure-

Induced Death (REID)

- Predictive analysis results showing crew lifetime radiation exposure limit data and goals



*Permissible Exposure Limits Stochastic Effects

Risk of Exposure Induced Death (REID)

due to cancer is limited to

level

Cancer incidence is reported as well

and is usually ~1.5x higher than mortality

*Reference: Edward Semones charts, 12/13/2011

Pre-Decisional, Internal Use Only

150mSv

SRAG recommends 150 mSv as crew lifetime exposure limit goal


Johnson Space Center- Houston, Texas *Projected Average Years of Life Lost per Death for an Exposure-induced Cancer for

Exposure Limit to 3% REID

Astronaut exposures have not exceeded the REID limit estimate and thus they have lower

years of life-loss


Pre-Decisional, For Internal Use Only



*Mission Doses





Analysis results of an ISS-derived architecture exposed to 365-days of GCR at EML1



The DSH ISS-derived concept is an in-line architecture that was analyzed for GCR protection performance at EML1/L2 for 365 consecutive days of exposure

module models, resulted in a range of internal dosage from 394 to 456 mSv

ISS-Derived, GCR Analysis Example

*

al, 12/2011.

Initial DSH Architecture/Point of Departure: *MSFC study/ ISS-Derived Deep Space Facility

Radiation Analysis Model of Similar ISS Elements

Lab + A/L tunnel + MPLM

Crewlock + Lab + Node



Risk of Exposure-Induced Death

Males about 47 years old or older are in range Females about 57 years old or older are in range Recall: design target GCR exposure of 150 mSv Effective Dose --- these dose values are 2 3 times higher

Far away from arriving at 150 mSv

Multiply these doses by 500+ days divided by 365 days for a short trip to Mars these radiation

space travel meeting the 3%REID at 95%CL at solar minimum levels For illustration purposes only, not representative

of formal exploration limits

*Analysis Reference: Janet Barzilla charts, 04/30/2012, Pre-Decisional

Notionally, this suggests that for a typical ISS structure exposure to 1 year at EML1:

*



Monolithic shield sizing for GCR: Aluminum, Polyethylene, water, liquid hydrogen



Shielding mass (g/cm2)

Shielding mass (kg)

Shielding launch cost ($50,000/kg)

Shielding launch cost ($5,000/kg)

1000 1.49 x 106 $9.7 x1010 $9.7 x109

500 7.4 x105 $1.9 x1010 $1.9 x109

100 1.5 x105 $9.6 x109 $9.6 x108

50 7.5 x104 $4.8 x109 $ 4.8 x108

10 1.5 x104 $9.6 x108 $9.6 x107

Shielding a small portion of the vehicle total habitable volume, say a cylinder 7 meters long and 5 meters in diameter (A = 149 m2; V = 137 m3) possibly feasible if launch costs and shielding mass requirements are low enough

Once again - The numbers used in the calculations are only estimates for the purpose of working the sample problem and do not represent any official NASA design or planning data

*Reference: Dr. S. Koontz charts, 01/31/2012


Approximated shielding estimate for an ISS Lab Module



* Physical thickness corresponding to areal densities

Areal density g/cm2

Aluminum Density = 2.7 g/cm3

Polyethylene or Water Density = 1.0 g/cm3

Liquid Hydrogen Density = 0.07 g/cm3

Boiling point = 20.28o K

1000 370 cm (146 in) 1,000 cm (394 in) 14, 285 cm (5624 in)

500 185 cm (72.8 in) 500 cm (197 in) 7,142 cm (2812 in)

100 37 cm (14.5 in) 100 cm (39.4 in) 1, 428 cm (562 in)

50 19 cm (7.5 in) 50 cm (20 in) 714 cm (281 in)

10 3.7 cm (1.5 in) 10 cm (4 in) 142 cm (56 in)

Thickness in cm = (areal density in g/cm2)/(density in g/cm3) *Reference: Dr. S. Koontz charts, 01/31/2012




Radiation Remarks

Although SPE shielding in the form of a specific storm shelter area will be incorporated into the DSH, we would not expect to generically use dead mass shielding as a primary go-forward solution for GCR

Continued architecture pathfinding study by investigating and conducting

DSH SE&I Study, continued



Analysis results of architecture exposed to 365-days of GCR at EML1



Hub and Spoke Architecture Hub and Spoke: centralized which possesses an internal layout where most of the crew activity takes place most of the time

Surround the core/hub with major structural elements that contain logistics, equipment, trash, prop, etc

Node in center, depicted here as surrounded radially by three MPLMs and an Airlock

Orion

FGB



The hopeful expectation would be that GCR analysis of the surrounded architecture would show a measurable shielding mass increase above the in-

so as to provide GCR reduction that is substantive enough to consider it as a smart architecture IF that much volume would be deemed necessary for the transit duration/application being considered.

<

this in-line architecture <g/cm2 this surrounded architecture

Comparison



was analyzed for GCR protection performance

Three examined inside the center Node showed a range of dosage from ~385 to 435 mSv for the surrounded architecture This is essentially very little change from the ISS-derived results which were a range from ~394 to 456 mSv for the in-line architecture

Hub and Spoke Architecture Concept Radiation Analysis Model of

Aluminum Weight-smeared Nodes

Real ISS Node model in center, 3 dose locations evaluated inside



Results Interpretation/Discussion Effective GCR Shielding

~40mSv reduction

About a doubling of the effective shielding thickness was successfully achieved using the surrounded architecture concept. However, the corresponding crew radiation dose reduction is only by about 10%, due to the Node shielding alone being somewhere along the knee of this curve, thus placing the additional shielding provided on the flatter part of this curve.

Node by itself, ~430 mSv

Prior to this analysis, ~15 g/cm2 was expected as an approx equivalent

shielding provided by an ISS module, but the Node is actually showing

closer to ~30 g/cm2



The Hub-and-Spoke/Surrounded architecture shows a slight favorable GCR reduction over the in-line, but not by a significant amount

The general intent was/should be to aspire for a vehicle architecture that provides below ~400 mSv of dose in a best effort possible

much lower/better than ~360 mSv out at 100 g/cm2, so getting as low as ~385 mSv is reasonable from just the vehicle architectural arrangement alone

for crew, which includes the additional protective effects of crew/human tissue and geometry in the analysis

If the Node 2 by itself (or any other module), offers an inherit shielding such as was shown of approximately 30 g/cm2, then the additional GCR protection

of a surrounded architecture will be limited to values along the flat part of the curve ie, it already possesses an efficient amount of shielding that buys you the most bang for the buck, and beyond that, the shielding weight penalty buys you far less GCR protection



Back - up



Radiation Primer, continued SPE GCR

Images from National Council on Radiation Protection (NCRP) Report No. 153 (2006)

Combined hydrogen, helium, oxygen and iron energy spectra for two large SPEs. The solid curves are fits to a stochastic particle acceleration model (adapted from Mazur et al., 1992).

Calculated differential energy spectra of hydrogen, helium, oxygen and iron for the 1976 to 1977 solar minimum and the 1989 to 1990 solar maximum.

Energy and Flux comparison

Higher Flux, Lower Energy Lower Flux, Much Higher Energy




DSH SE&I Results to Date

SPE GCR Shielding is not conducive for

protecting against GCR.

SPE radiation is effectively curtailed by shielding. Shielding has profoundly less affect against GCR; lifetime limit goal is well below.

250 mSv ~lifetime limit for 40*-yr female

400 mSv ~lifetime limit for 40*-yr male

* Effective dose lifetime ceiling/limit is lower below this age.

~15 g/cm2 is approx equivalent shielding provided

by an ordinary ISS module

, One-year dose , One-year dose for an idealized spherical shield for an idealized spherical shield



Shielding Assessment Technology Software tool (Pro/Engineer + Fishbowl

tool kit) Ray Tracing technology

Evenly distributed rays (up to 1 million rays) are created to start from dose point and end outside the vehicle.

Each Ray records distance and respective density of the parts it passes

Areal mass density is calculated.

Areal mass density is used in transport code that evaluates particle flux at dose point.

Dose point



Ray Tracing (Dose Points)

locations of dose points inside MTV that were used in ray tracing



Hot Spots Detection Capabilities

Every ray is color coded according to the areal density value-Shielding- it provides.

Only one dose point at a time-multiple colors

Single dose point Color Coding



Every ray that provides less than 10 g/cm2 shows up as a red pixel

on the MTV surface.

Multiple dose points-single color

Hot Spots Detection Capabilities

Multiple dose point Hotspot detection



Hot Spots Detection Capability

Initial design

Initial Design: Hotspots are shown on sides of habitat.



*ALARA As Low As Reasonably Achievable

The ALARA principle is a legal requirement intended to ensure astronaut safety. An important function of ALARA is to ensure that astronauts do not approach radiation limits and that such

in view of the large uncertainties in cancer and other risk projection models. Mission programs and terrestrial occupational procedures resulting in radiation exposures to astronauts are required to find cost-effective approaches to implement ALARA.

Challenges: Uncertainties in biological response to the high-LET component of GCR make ALARA difficult to implement. ALARA is more easily performed for reducing SPE exposure using shielding and limiting exposures during EVAs





*Our Guidelines: NASA-STD-3001

4.2.2.2 Space Permissible Exposure Limits (SPEL) - Quantifiable limit of exposure to a space flight factor over a given length of time (e.g., lifetime radiation exposure). Physical/chemical agent measured. 4.2.10 Space Permissible Exposure Limit for Space Flight Radiation Exposure Standard

4.2.10.1 Planned career exposure for radiation shall not exceed 3 percent risk of exposure induced death (REID) for fatal cancer. 4.2.10.2 NASA shall assure that this risk limit is not exceeded at a 95 percent confidence level using a statistical assessment of the uncertainties in the risk projection calculations to limit the cumulative effective dose (in units of Sievert) received by an astronaut throughout his or her career. 4.2.10.3 Exploration Class Mission radiation exposure limits shall be defined by NASA based on National Council on Radiation Protection (NCRP) recommendations. 4.2.10.4 Planned radiation dose shall not exceed short-term limits as defined in table 4 in Appendix F supporting material for the radiation standard. 4.2.10.5 In- achievable (ALARA) principle.

*Reference: Janet Barzilla charts, 04/30/2012


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