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

Rel

ativ

e C

ontr

ibut

ion

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

LeadTin

CopperAluminum

PETI -5Al(5 g cm-2) + CH2 (2 g cm-2)

CH2/ Li6Al(5 g cm-2) + CH2 (5 g cm-2)

LiFCH2/ 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

EpoxyBe

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.