This viewgraph presentation reviews the risk factors from space radiation for astronauts on future lunar missions. Two types of radiation are discussed, Galactic Cosmic Radiation (GCR) and Solar Particle events (SPE). Distributions of Dose from 1972 SPE at 4 DLOCs inside Spacecraft are shown. A chart with the organ dose quantities is also given. Designs of the exploration class spacecraft and the planned lunar rover are shown to exhibit radiation protections features of those vehicles

Cucinotta, Francis A.

Feiveson, Alan H.

Hayat, Mathew

Kim, Myung-Hee Y.

Nounu, Hatem N.

NASA Technical Reports Server

Minimizing Astronauts’ Risk 
from Space Radiation
during Future Lunar Missions
Myung-Hee Y. Kim1, Matthew Hayat2, Hatem N. Nounu3, Alan H. Feiveson4, 
and Francis A. Cucinotta4
1Wyle Laboratories, Inc., Houston, TX  77058, USA
2Universities Space Research Association, Houston, TX  77058, USA
3University of Houston, Houston, TX  77058, USA
4NASA Johnson Space Center, Houston, TX  77058, USA
12th WRMISS, September 10-12, 2007, Stillwater, Oklahoma, USA
https://ntrs.nasa.gov/search.jsp?R=20070029991 2019-08-30T01:33:14+00:00Z
Problem
• Continuous galactic cosmic rays (GCR) pose a serious health 
risk to humans and contribute to failure rates for electronics 
during space missions.  The risks must be predicted accurately 
for future lunar missions.
Æ We develop a practical approach of expected GCR 
environment.
• Solar particle events (SPEs) are a concern for space missions 
outside Earth’s geomagnetic field.
• The sporadic occurrence of SPEs and number of large SPEs in 
a short period are major operational problems  for planning 
space missions and protecting humans during missions.
Æ We develop a probability of large SPE during a given mission 
duration.
An integrated strategy for radiation protection on 
lunar exploration missions.
-2000
0
2000
1950 1960 1970 1980 1990 2000 2010 2020
Time
φ
,
 
M
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0
5
10
15
20
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GCR Deceleration Potential
Point Dose Equivalent (5 g/cm2 Al) 
Free Space
LEO
GCR Environment
and
Point Dose Equivalent inside Spacecraft 
Database of Solar Particle Events
Solar Cycle # of SPE # of Day Period Fluence, ΦE
Cycle 23 92 3897 5/1/1996-12/31/2006 Φ10,30,50,60,100(1)
Cycle 22 77 3742 2/1/1986-4/30/1996 Φ10,30,50,60,100(1)
Cycle 21 70 3653 2/1/1976-1/31/1986 Φ10,30(2)
Cycle 20 63 4140 10/1/1964-1/31/1976 Φ10,30(2) and Φ10,30,60(3)
Cycle 19 68 3895 2/1/1954-9/30/1964 Φ10,30,100(2) and Φ10,30(4)
Impulsive Nitrate Events 71 390 years 1561 - 1950 Φ30(5 and 6)
Energy Spectra(7 and 8) or Weibull Distribution Function(9 and 10)
(1)  GOES SEM data: http://goes.ngdc.noaa.gov/data/
(2)  Feynman, Armstrong, Dao-Gibner, and Silverman, J. Spacecraft, 27, No. 4, pp. 403-410, July-August, 1990.
(3)  King, J. H., solar proton fluences for 1977-1983 space missions, J. Spacecraft, 11, No. 6, pp. 401-408, June 1974.
(4)  Shea and Smart, Solar Physics, 127, pp. 297-320, 1990.
(5)  McCracken, K. G., Dreschhoff, G. A. M., Zeller, E. J., Smart, D. F., and Shea, M. A., Solar cosmic ray events for the period 
1561-1994, 1. Identification in polar ice, 1561-1950. J. Geophys. Res., 106, No. A10, 21585-21598, October 1, 2001.
(6)  Siverman, S., Silverman catalog of ancient auroral observations, 666BCE to 1951, 
http://nssdc.gsfc.nasa.gov/space/auroral/auroral.html, 2002.
(7)  Freier, P. S. and Webber, W. R., “Exponential Rigidity Spectrums for Solar-Flare Cosmic Rays,” J. Geophys. Res., Vol. 68, 
No. 6, 1963, pp. 1605-1629.
(8)  Biswas S., Fichtel, C. E., and Guss, D. E., “Study of the Hydrogen, Helium, and Heavy Nuclei in the November 12, 1960 
Solar Cosmic-Ray Event,” Phys. Review, Vol. 128, No. 6, 1962, pp. 2756-2771.
(9)  Kim, M. Y., Cucinotta, F. A., and Wilson, J. W., A temporal forecast of radiation environments for future space exploration 
missions, Radiat. and Environ. Biophys., 46, No. 2, pp. 95-100, June 2007.
(10) Xapsos et al., IEEE Trans. Nuc. Sci. 47(6), 2218-2223, 2000.
Space Era
Extended with Ice Core Data
Cumulative Distributions of Sample 
SPE Populations
Cumulative Distributions of Sample SPE Populations
0.01%
0.10%
1.00%
10.00%
100.00%
1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11
Size of Event (>Φ 30)
C
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m
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l
a
t
i
v
e
 
%
Space Era
Extended with Ice Core Data
200
400
600
800
1000
1200
1400
1600
1800
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020
Year
Φ
,
 
M
V
+ + + +
- - -
1/1/1950  1/1/1960  1/1/1970  1/1/1980  1/1/1990  1/1/2000  1/1/2010  1/1/2020  
F
(
>
3
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V
)
,
 
P
r
o
t
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/
c
m
2
108
109
1010 F>108 solar proton
events only
GCR Deceleration Potential
SPE Probability in 2-Week Mission and BFO Exposure Level 
inside a Typical Equipment Room in Free Space
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11
Size of Event (>Φ30)
S
P
E
/
M
i
s
s
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n
0.1
1
10
100
1000
B
F
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Average Probability of Space Era  
Extended Average Probability
Probability of Impulsive Nitrate Events
BFO Dose of Worst Case SPE Model
BFO Dose of SPE during Space Era
NCRP 30-day limit at BFO for LEO mission
SPE Probability in 1-Week Mission and BFO Exposure Level 
inside a Typical Equipment Room in Free Space
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11
Size of Event (>Φ30)
S
P
E
/
M
i
s
s
i
o
n
0.1
1
10
100
1000
B
F
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D
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c
G
y
-
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Average Probability of Space Era 
Extended Average Probability
Impulsive Nitrate Events
BFO Dose of Worst Case SPE Model
BFO Dose of SPE during Space Era
NCRP 30-day limit at BFO for LEO mission
Probability of SPE with Φ30 > 2 x 109 cm-2
in 1-Week Mission
Sample P(Φ30 ≥ 2×109 cm-2)
SPEs in Space Era 0.39 % ± 0.4 %
SPEs in Space Era + the interval 1561-1950 0.49 % ± 0.39 %
Observation SPEs in the interval 1561-1950 0.47 %
Calculation
Hazard Model of SPE Gap Times
Histogram of Event Size, log(Φ30)
Event Threshold Φ30=107 cm-2
Cumulative Probability during a Given Mission Period 
Event Threshold Φ30=107 cm-2
Event Threshold Φ30=108 cm-2 Event Threshold Φ30=109 cm-2
Structural Distribution Model Using ProE™
Various Composition Layers for Exploration-Class 
Spacecraft
Ray Tracings at 4 DLOCs inside Spacecraft 
Shielding Distributions at 4 DLOCs of Spacecraft
Random Orientation
• Discrete number of evenly 
scattered rays over 4π solid angle
• Isotropic angular distribution (for 
the same volume element):
p(μ) = constant
Aligned Orientation
• A continuously distributed source 
rays
• Cosine angular distribution in a 
small interval on spherical polar 
coordinates (for each volume 
element):
p(μ) = μ
μ= cos θ θ
Idealization of the Actual Motion of Astronauts
μ= cos θ
Random Orientation
where 
N = the given number of rays
Xi = the amount of shielding by 
material composition layers at the 
ith ray
Aligned Orientation
where 
θ = polar angle of a ray
φ = azimuth angle of a ray
X(θ,φ) = the integrated thickness of 
shielding by spacecraft of a ray
Y(θ,φ) = the thickness of body 
shielding of a ray   
∑
=
=
N
i
iorganorgan XHN
H
1
)(1 ( )
Idealization of the Actual Motion of Astronauts
∫ ∫
−=
+= 2
2
),(),(cos
π
πθ
φθφθφθθ YXHddHorgan
Distributions of Dose 
from 1972 SPE 
at 4 DLOCs inside Spacecraft

Directional Dose Distribution inside Spacecraft
Various Composition Layers for Exploration-Class 
Spacecraft
Organ Dose Quantities for Two Orientations
August 1972 SPE
 
Random orientation Aligned orientation  
DLOC1 DLOC2 DLOC3 DLOC4 DLOC1 DLOC2 DLOC3 DLOC4 
X-coordinate, cm 
Y-coordinate, cm 
Z-coordinate, cm 
43.18 
119.38 
52.71 
-43.18 
119.38 
52.71 
40.64 
119.38 
-79.34 
-40.64 
119.38 
-79.34 
43.18 
119.38 
52.71 
-43.18 
119.38 
52.71 
40.64 
119.38 
-79.38 
-40.64 
119.38 
-79.38 
Al-Eq xavg, g/cm2 15.18 15.08 15.85 15.33 15.18 15.08 15.85 15.33 
xmin - xmax 0 - 102.07 0 - 105.50 0 – 83.21 0 - 85.79 0 - 102.07 0 - 105.50 0 – 83.21 0 - 85.79 
Avg skin      126.61 121.07 104.08 108.59 150.92 135.41 111.45 114.45 
Eye           86.76 84.36 73.58 77.06 89.71 89.94 81.62 79.72 
Avg BFO       16.91 16.82 15.2 15.88 18.14 18.20 16.05 15.98 
Stomach      7.38 7.37 6.77 7.03 6.94 6.89 6.59 6.63 
Colon        14.42 14.36 13.04 13.6 14.46 14.36 12.67 12.79 
Liver        10.37 10.33 9.41 9.8 9.43 9.60 8.92 9.23 
Lung         12.16 12.12 11.04 11.5 12.09 11.61 11.30 10.73 
Esophagus   11.61 11.57 10.54 10.98 11.25 10.78 10.52 9.93 
Bladder    7.54 7.53 6.9 7.17 7.64 7.25 6.98 6.84 
Thyroid    18.39 18.31 16.55 17.28 18.55 18.15 16.47 16.79 
Chest             72.23 70.58 61.85 64.83 74.88 73.95 67.60 66.37 
Gonads       35.27 34.74 30.76 32.24 37.72 32.64 31.19 27.74 
Front brain 29.54 29.32 26.31 27.53 28.72 27.60 25.32 25.32 
Mid brain 16.2 16.15 14.68 15.3 15.52 15.56 14.05 15.03 
CAM 
organ 
dose, cSv 
Rear brain 28.93 28.72 25.79 26.98 27.49 27.96 24.98 27.84 
Effective dose eq, cSv 21.45 21.16 18.89 19.75 22.42 21.09 19.43 18.64 
Point dose eq, cSv 254.68 242.74 207.92 216.83 253.48 241.76 205.76 211.88 
 
Rover Design
2
0
 
c
m
• Three sections 
of rover: front, 
center, and 
back.
• Wall thickness:
1 g/cm2
120 cm
110 cm
60 cm
280 cm
60 cm
136 cm 140 cm
50 cm 50 cm
600 cm
130 cm
156 cm
230 cm
130 cm
200 cm
Schematic Drawings of Rover With and Without
Polyethylene Shelter in the Center Section
Rover without 
polyethylene 
shield in central 
shelter
Rover with 
polyethylene 
shield in central 
shelter
2
0
 
c
m
Wall thickness
Aluminum = 0.37 cm
or
Graphite/Epoxy =0.657 cm
Polyethylene thickness=1, 3, or 5 g/cm2
Wall thickness
Aluminum = 0.37 cm
or
Graphite/Epoxy =0.657 cm
SPE Shelter Concepts on Rover
Rover 
section 
Section 
mass of  
1 g/cm2, 
kg 
Rover 
mass, 
kg 
Polyethylene 
SPE shelter 
thickness, 
g/cm2 
Polyethylene 
shelter mass, 
kg 
Total 
mass, kg 
Front 201 1  166 720
Center 188 3 490 1044
Back 165
554 
 
5 800 1354
 
EVA Exposure (in cSv) Inside Polyethylene Shelter for 
Two Rover Concepts
on Lunar Surface from August 1972 SPE
Polyethylene thickness of SPE shelter in the rover 
1 g/cm2 3 g/cm2 5 g/cm2 
Organ Al Rover 
Graphite/Epoxy 
Rover Al Rover
Graphite/Epoxy 
Rover Al Rover
Graphite/Epoxy 
Rover
Skin 358.05 320.48 116.20 107.92 49.99 47.09
Eye 277.52 252.14 100.40 93.69 45.17 42.66
Avg. BFO 34.46 32.58 17.69 16.88 9.81 9.44
Stomach 12.00 11.51 6.97 6.74 4.27 4.17
Colon 27.61 26.21 14.72 14.10 8.39 8.10
Liver 19.17 18.23 10.36 9.94 6.01 5.82
Lung 22.40 21.32 12.20 11.70 7.08 6.85
Esophagus 21.30 20.27 11.62 11.15 6.76 6.54
Bladder 12.93 12.35 7.26 7.00 4.35 4.24
Thyroid 37.13 35.14 19.22 18.35 10.70 10.30
Chest 221.87 202.84 84.16 78.68 38.61 36.51
Gonads 95.46 88.38 40.27 37.88 19.59 18.62
Front brain 66.16 62.20 32.12 30.50 17.05 16.33
Mid brain 30.33 28.85 16.45 15.77 9.47 9.15
Rear brain 64.30 60.48 31.38 29.81 16.72 16.01
Point dose 801.89 713.90 249.65 230.94 104.10 97.61
Whole body 
effective dose 51.94 48.27 23.10 21.85 11.88 11.36
 
Summary
• A temporal forecast of GCR has been derived from the GCR deceleration 
potential (φ) - Point dose equivalent in interplanetary space is influenced by
solar modulation by a factor of 3.
• Relationship between large SPE occurrence and φ is clearly shown.
• Exposure levels of 34 big SPEs and worst-case SPEs:
- Most SPEs lead to small BFO doses in an unshielded typical equipment 
room (< 12.5 cGy-Eq on lunar surface).
• Probabilities of one and multiple SPEs with event size thresholds are 
obtained for various mission durations.
• Detailed distribution of directional risk assessment shows better 
protection for risk mitigation inside a habitable volume/shelter/spacecraft 
during future lunar missions.
• A large SPE similar to August 1972 event can be shielded to an effective
dose <150 mSv by an SPE shelter on rover during EVA on lunar surface.


Minimizing Astronauts' Risk from Space Radiation during Future Lunar Missions

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