Space Radiation Health Effects of Astronauts in Explorative Missions

Günther Reitz

Radiation Biology DepartmentInstitute of Aerospace MedicineGerman Aerospace Center (DLR)

‘Fault tree’ of Fatal event

Fluxes of primary space radiation components

innerVan Allen belt

protons

Effective Doses Low Earth Orbit Missions and Missions to the Moon

GCR exposure in interplanetary space

DLRBON2010BON2011

BON2011/

BON2010≈ 1.35

BON2011/DLR

≈ 1.1

Worst$ case' SPE radiation exposures in Sv during different mission phases for critical tissues under

different mass shielding

Limits for Astronauts in LEO (NASA as example)

Career non-cancer and Short term effects

Career cancer risk limits

Effective Dose (Sv)Age Male Female25 0.7 0.435 1 0.645 1.5 0.955 3 1.7

Dose (Gy-Eq)BFO Eye Skin

Career NA 4.0 4.0Annual 0.5 2.0 3.030 days 0.25 1.0 1.5

For reference: Limits for radiation workers on Earth: 20 mSv annual and 400 mSv career

How Astronauts are Affected by Cosmic Rays?

DNA damage

-Cell cycle arrest-Repair

-Cellular Survival

-Clonal Expansion

Energy deposition

-Transformation

-Mis-repair

-Mutations

-Carcinogenesis

DNA is the MainTarget of Radiation Action

-Cell death, e.g. by-Apoptosis-Misdifferentiation-Senescence

-No repair

Radiation Effects

.early morbidity

..prodromal syndrome

...fatigue, aneurexia,

...nausea, diarrhea, vomiting ..erythema ..cataracts

early mortality ..hematopoetic death

..performance decrement

Early (deterministic) Effects

.cancer, .cataracts, .hereditary/teratogenic

..incidence,

..mortality

Late (stochastic) Effects

Early morbidity/mortality for worst case SPE behind 10 gm/cm2 in interplanetary space

earlymorbidity

earlymortality

How Real are Radiation Risks for Astronauts from SPEs ?

0

0.1

0.2

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0.5

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0.9

1

Pro

bab

ility

Cycle 19

Cycle 20

Cycle 21

Cycle 22

Cycle 23

Impulsive Nitrate Events

Nitrate Events with Correction

Space era

108104 105 106 109107 1010

Event Size (F30), p cm-2

104 105 106 107 108 109 1010

Fluence of protons with energy >30 MeV per event in cm-2

1.0

0.9

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Pro

ba

bili

ty Cycle 19 Cycle 20 Cycle 21 Cycle 22 Cycle 23— Space era

Uncertainties in Radiation Risk Projection Risk Projections

1%

0.1%

0.01%

-Maximum Acceptable Risk

-Shuttle Mission

-ISS Mission

-▲

-▲

-▲

-Point Estimate

-“95% Confidence Interval”

10%

-95% Confidence Interval

-Individual’s Fatal Risk

-Lunar-▲

-SPE??

-Mars

Major sources of uncertainty of risk estimation from space radiation field

Radiation Risk in a 550 day mission to Mars

Cucinotta (Space Radiation Risk Calculation)

45 Year old male, US Population, 20g/cm^2 shielding

- Aug 72 Solar Particle event, 340 mSv

REID 0.98 % (0,23;2.59)

- 550 day Mission to Mars GCR ,550 mSv)

REID 2.00 % (0.33;5.01)

ICRP

- 550 day mission

Excess Risk/Sv 4x 10^-2 results in 3.6%

Significance of Shielding Material for GCR (20g/cm^2 shielding, 40-yr males)

-f

-Light Light Flash Observations

Age, yr35 40 45 50 55 60 65 70

Su

rviv

al w

ith

ou

t C

ata

racts

0.2

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Low-dose astronauts(ave. dose 3.6 mSv)

High-dose astronauts

Age, yr40 45 50 55 60 65 70

Low-dose astronauts

High-dose astronauts(ave. dose = 45 mSv)

High-dose astronauts

All Cataracts Non-trace Cataracts

Astronaut Cataracts: Space Radiation

-RBE ~ 200 !!

Observation of Cataracts

F. A. Cucinotta et al., 2001

Countermeasures against radiation effects

• develop proper risk criterion for exploratory LONG term missions

• integrate radiation risk assessment into total risk analysis

• reduce uncertainties for exposure estimates

• reduce uncertainties for dose effect relations (late & early)

Improve

advance

risk

assessment

• optimise shielding design, include storm shelters (material & thickness )

• optimise mission design

– duration

– timeline relative to solar activity cycle

– guarantied shelter accessibility

• advance forecasting capabilities for solar particle events

• monitor and document exposure history and health status

Minimise

radiation

exposure

Maximise

radiation

resistance

• select genetically resistant individuals

• modify dose response curve of ‘normal’ crew members

– attenuate early effects by prior and post medication

– mitigate late effects by prophylactic nutrition

Radiation Assessment Detector (Cruise Measurements)

SPE Exposures mSv23-29 Jan 4 7-15 March 19.517-18 May 1.2

GCR Exposure/day 1.8

Conclusions

GCR Risks•Stochastic effects such as cancer induction and mortality or late deterministic effects, such as cataracts or damage to the central nervous systems are of concern•Doses present no acute health effects in deep space missions•There are no data for human exposures to these radiation to estimate risks of astronauts•Usual methods of estimating risk by calculating dose equivalent or equivalent dose are questionable to be appropriate for these particles•Upper 95% C.I. for excess cancer risks from GCR for an mission to Mars may exceed current limits defined for Low Earth Orbits •During interplanetary cruise shielding is limited and will therefore not significantly reduce GCR risks

SPE Risks•Risks are manageable by shielding measures•Shielding should limit excessive exposure to prevent acute effects•Hydrocarbon shields offer a reduction of a factor of two compared to Aluminium•Exploration vehicles shielding should focus on SPE instead on GCR

SPARES

Solar corona and sudden release of a huge clouds of particles

Excess Relative Risk as a function of rate of exposure

Gregoire O. et.al., Radiat. Biol., 2006

Excess Relative Risk as function of dose rate

Fatal Cancer Risks near Solar Minimum (20 g/cm^2 shielding)

www.DLR.de • Chart 26

-Slide Courtesy of F. A. Cucinotta

Fatal Cancer Risk Near Solar Maximum (PHI=1100MV including 1972 SEP)

www.DLR.de • Chart 27

-Slide Courtesy F. A. Cucinotta