Mars Mission Radiation Dose/Shielding Summary Note: Dr. Cary Zeitlin generously contributed these...
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Transcript of Mars Mission Radiation Dose/Shielding Summary Note: Dr. Cary Zeitlin generously contributed these...
Mars Mission Radiation Dose/Shielding Summary
• Note: Dr. Cary Zeitlin generously contributed these slides from two full-length presentations. For brevity’s sake, supporting details have been removed. Use at your own risk…
• Contributor Credits: Cary Zeitlin (SwRI), NASA, Lawrence Berkeley National Lab
• Collator: Brian Enke (SwRI)
Dose
Dose is physical: energy deposited per unit mass.
1 gray = 1 Gy = 1 J / kg = 100 rads
Dose equivalent
• 1 sievert = 1 Sv = 100 rem. • Sv dffers from Gy by weighting factor:
– wR = 1 for sparsely-ionizing types, e.g., g– wR = 5 for protons, 20 for a and heavier
nuclei.• In “mixed field” wR replaced by Q(L).
Shielding against GCR is impractical.
Some exposure to heavy ions is inevitable in space.
DNA repair works for simple damage, but heavy ions cause complex damage.
15th Humans in Space, Graz, Austria
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Nuclear Charge
Re
lati
ve
Co
ntr
ibu
tio
n
FluxDoseDose equivalent
1%
0.1%
.01%
Maximum Acceptable Risk = 3%
Shuttle Mission
ISS Mission
Mars Mission
Increase in Individual’s Risk of Fatal Cancer
▲
▲
▲
“95% Confidence Interval”
10%
Lunar▲
SPE??
15th Humans in Space, Graz, Austria
Dose Reduction Chart Revisited
• Hydrogen clearly superior as predicted by Wilson et al.• Best-performing composites give results similar to CH2.
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Lead
Tin
Copper
Aluminum
PETI -5
Al(5 g cm-2) + CH2 (2 g cm-2)
CH2/ Li6
Al(5 g cm-2) + CH2 (5 g cm-2)
LiF
CH2/ LiC
CH2 (17 g cm-2)
CH2 + Boron
Graphite Epoxy (10 g cm-2)
Carbon
Graphite Epoxy (5 g cm-2)
Martian Regolith + CH2
CH2 (5 g cm-2)
Boron-Epoxy
Epoxy
Be
H (estimated)
Dose reduction per g cm-2
Conclusions from ODY
GCR ~ as expected from models & near-Earth data.Radial gradient for solar particles is large SPE weaken as they propagate out to Mars.Need ground truth – surface environment more complex.
GCR transport model calculation from NASA-JSC.Unshielded doses ~ 1000 times greater on Mars than Earth but lower than free space by factor of 2.Surface well-shielded from most SPEs.
Annual dose-equivalent (Sv/yr)
Mars Science Laboratory
Next Mars rover
Launches Nov. 2011.
Includes RAD, a small (1.5 kg) but capable detector with neutron capability.