Space Radiation Health Effects of Astronauts in Explorative Missions
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Space Radiation Health Effects of Astronauts in Explorative Missions
Günther Reitz
Radiation Biology DepartmentInstitute of Aerospace MedicineGerman Aerospace Center (DLR)
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‘Fault tree’ of Fatal event
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Fluxes of primary space radiation components
innerVan Allen belt
protons
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Effective Doses Low Earth Orbit Missions and Missions to the Moon
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GCR exposure in interplanetary space
DLRBON2010BON2011
BON2011/
BON2010≈ 1.35
BON2011/DLR
≈ 1.1
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Worst$ case' SPE radiation exposures in Sv during different mission phases for critical tissues under
different mass shielding
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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
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How Astronauts are Affected by Cosmic Rays?
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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
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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
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Early morbidity/mortality for worst case SPE behind 10 gm/cm2 in interplanetary space
earlymorbidity
earlymortality
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How Real are Radiation Risks for Astronauts from SPEs ?
0
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bab
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Cycle 19
Cycle 20
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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
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Pro
ba
bili
ty Cycle 19 Cycle 20 Cycle 21 Cycle 22 Cycle 23— Space era
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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
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Major sources of uncertainty of risk estimation from space radiation field
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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%
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Significance of Shielding Material for GCR (20g/cm^2 shielding, 40-yr males)
-f
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-Light Light Flash Observations
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Age, yr35 40 45 50 55 60 65 70
Su
rviv
al w
ith
ou
t C
ata
racts
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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
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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
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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
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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
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SPARES
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Solar corona and sudden release of a huge clouds of particles
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Excess Relative Risk as a function of rate of exposure
Gregoire O. et.al., Radiat. Biol., 2006
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Excess Relative Risk as function of dose rate
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Fatal Cancer Risks near Solar Minimum (20 g/cm^2 shielding)
www.DLR.de • Chart 26
-Slide Courtesy of F. A. Cucinotta
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Fatal Cancer Risk Near Solar Maximum (PHI=1100MV including 1972 SEP)
www.DLR.de • Chart 27
-Slide Courtesy F. A. Cucinotta