Page 1 ... Optimized design of future Martian Transport. Vehicle (MTV) prototype and calculated ... Software tool (Pro/Engineer + Fishbowl tool kit). ⢠Ray Tracing ...
Radiation Shielding Evaluation Tool for Risk Reduction on Future Human Space Missions Hatem N. Nounu and Myung-Hee Y. Kim Universities Space Research Association, Houston, Texas 77058, USA And Francis A. Cucinotta UNLV- currently
July 19th, 2012
Outline • Radiation challenge in extended space missions such as to Moon, Mars, or Near Earth Asteroids (NEAs) • Challenges to accurate risk assessment • Predictive software capability • Optimized design of future Martian Transport Vehicle (MTV) prototype and calculated risks to humans • Summary
Radiation Challenge • Moon, Mars, or NEA missions require prolonged stay in deep space • Astronauts are exposed to different types of radiation in deep space, mainly GCR and SPE • Protection from radiation in habitable area is required but faces the challenge of limited payload.
Fishbowl Tool Flat Lunar Surface
Dose point on flat lunar surface
Lunar Basin
Dose point in center of basin
Lunar Cliff
Dose point at bottom of a high cliff
Predictive Software Capability • Shielding assessment technology (FishBowl) • Dose and Particle Fluence – Transport code: HZETRN, BRYNTRN – Nuclear Interaction Model : QMSFRG
• Cancer risk model (NASA Space Cancer Risk (NSCR) code) • Future - Stochastic Transport model: the GERMCode (GCR Event Based Risk Model), for advanced health risk modeling
GERMCode comparison to NSRL Data
Shielding Assessment Technology Software tool (Pro/Engineer + Fishbowl tool kit)
• Ray Tracing technology – Evenly distributed rays (up to 1 million rays) are created to start from dose point and end outside the vehicle. – Each Ray records distance and respective density of the parts it passes
– Areal mass density is calculated. – Areal mass density is used in transport code that evaluates particle flux at dose point.
Dose point
Software tool (Pro/Engineer + Fishbowl) Hotspot Detection Capability • Goal is to color hotspots in red – Ray tracing multiple dose points, up to 20 dose points, distributed in key locations around the model, and showing the rays at same time as they exit the outer surface of the design. – From all dose points show only 1 inch of the rays at the surface without showing the part of rays inside craft. – User sets threshold value below which the ray will appear in red and above which it will disappear.
Lunar topography shielding effects
Lunar surface includes plateaus, basins, and cliffs that can serve as a shield for spacecrafts
Lunar topography analysis • Lunar Surface is modeled by an Aluminum basin with the capsule at the center of its cavity. • Dose point was placed in the center of a 300 cm diameter spherical aluminum capsule—5 g/cm2 thick—placed on the aluminum basin. • The entire assembly was ray-traced using Pro/E-Fishbowl to calculate the equivalent Al thickness of the capsule and basin together. • Any ray that passes through the basin body goes will not contribute to the radiation dose. • The analysis was performed for the following cases: 1- on flat surface 2- in center of basin 1:5 depth:diameter ratio 3- in center of basin 1:10 depth:diameter ratio 4- near the bottom of a very steep cliff
Capsule on flat surface Aluminum capsule 300 cm diameter 5 g/cm2 thick
Aluminum surface
• On flat surface: 50% of rays are blocked.
Capsule in Basin: 1:5 & 1:10 aspect ratio Aluminum capsule
1:5 aspect ratio basin 1:10 aspect ratio basin
• 1:5 aspect ratio basin: 69% of rays are blocked • 1:10 aspect ratio basin: 60% of rays are blocked
Capsule near the bottom of a cliff Aluminum capsule
• Near the bottom of cliff: 75% of rays are blocked.
Graphical representation of shielding Flat Lunar Surface
Dose point on flat lunar surface
Lunar Basin
Dose point in center of basin
Lunar Cliff
Dose point at bottom of a high cliff
• Near the bottom of cliff is optimum lunar site
Lunar rover prototype (Fred) thickness Poly=1.053 ~ 5.265 cm
Wall thickness Aluminum = 0.37 cm
600 cm
0.55 100 cm 160 cm
200 cm
150 cm 100 cm
0.55
0.40 130 cm 130 cm
130 cm
50 cm 250 cm
125 cm
50 cm
130 cm
Material: Aluminum, Graphite/Epoxy Composite and polyethylene Shape: 3 sections—front, center (shelter), back Thickness: Aluminum = 1g/cm2 Graphite/Epoxy Composite = 1g/cm2 Polyethylene = varying from 1 g/cm2 in areas protected by front and back sections to 5 g/cm2 on the sides and top with no protection from the bottom.
CAD design of lunar vehicle Aluminum shelter with Poly shield inside
Aluminum Front section
Aluminum Back section
• Polyethylene layer in shelter with varying thickness
Rover shelter optimization Aluminum=1 g/cm2 Polyethylene=5 g/cm2 Polyethylene=1 g/cm2
Cross section of lunar vehicle showing the poly shield thickness optimization inside shelter
Dose Point in Central Shelter for Rover With and Without Polyethylene Shielding
Cross section of Aluminum Rover without polyethylene shield in central shelter
Cross section of Aluminum Rover with polyethylene shield in central shelter
Shielding optimization
Optimized rover was placed near lunar cliff and the assembly was ray traced.
Whole body effective dose Table 1. Effects of polyethylene shelter and lunar cliff on whole body effective dose for Aluminum and Graphite /Epoxy composite cases. Rover
Aluminum Rover
Composite Rover
Rover material + SPE Shelter (Polyethylene)
Rover mass, Kg
E, cSv
Aluminum + 0 g/cm2 Polyethylene
554
86.63
Aluminum + 1 g/cm2 Polyethylene
721
49.12
Aluminum + 3 g/cm2 Polyethylene
1044
21.09
Aluminum + 5 g/cm2 Polyethylene
1112
10.61
Optimized AL Rover: Aluminum + 0 to 5 g/cm2 Polyethylene
933
14.54
Optimized AL Rover near Cliff
933
6.91
Graphite/Epoxy + 0 g/cm2 Polyethylene
554
77.88
Graphite/Epoxy + 1 g/cm2 Polyethylene
721
45.59
Graphite/Epoxy + 3 g/cm2 Polyethylene
1044
19.94
Graphite/Epoxy + 5 g/cm2 Polyethylene
1112
10.14
Optimized Composite Rover: Graphite/Epoxy+ 0 to 5 g/cm2 Polyethylene
933
13.44
Optimized Composite Rover near Cliff
933
6.18
Table 2. Topography Effect on Radiation Exposure inside Aluminum capsule and optimized rover from August 1972 SPE. Table shows organ dose and whole body effective dose for each case.
Aluminum Capsule of 5 g/cm2 Thick Organ dose, cSv
Interplanetary Space
Flat Area
Basin 1:10 (h:d ratio)
Basin 1:5 (h:d ratio)
Near Cliff
Aluminum Rover Near Cliff
Point dose
539.10
270.09
217.42
167.39
133.21
68.33
Skin
240.47
120.47
96.98
74.66
59.42
32.18
Eye
195.23
97.81
78.74
60.62
48.24
28.18
Avg BFO
30.53
15.30
12.31
9.48
7.54
5.5
Stomach
11.15
5.59
4.50
3.46
2.75
2.32
Colon
24.99
12.52
10.08
7.76
6.18
4.66
Liver
17.31
8.67
6.98
5.37
4.28
3.32
Lung
20.44
10.24
8.24
6.35
5.05
3.9
Esophagus
19.43
9.73
7.83
6.03
4.80
3.72
Bladder
11.79
5.91
4.75
3.66
2.91
2.38
Thyroid
33.14
16.60
13.37
10.29
8.19
5.99
Chest
161.16
80.74
65.00
50.04
39.82
23.78
Gonads
74.55
37.35
30.07
23.15
18.42
11.67
Front Brain
56.90
28.51
22.95
17.67
14.06
9.73
Mid brain
27.79
13.92
11.21
8.63
6.87
5.23
Rear brain
55.49
27.80
22.38
17.23
13.71
9.52
Effective dose
60.03
30.07
24.21
18.64
14.83
6.91
Table 3. Topography Effect of Radiation Exposure inside Graphite/Epoxy Composite capsule and optimized rover Spacecraft from August 1972 SPE. Table shows organ dose and whole body effective dose for each case. Graphite/Epoxy Composite Capsule of 5 g/cm2 Thick Organ dose, cSv
Basin 1:10 (h:d ratio)
Basin 1:5 (h:d ratio)
Near Cliff
Graphite/Epoxy Rover Near Cliff
Interplanetary Space
Flat Area
Point dose
384.50
192.6 3
155.07
119.39
95.01
57.51
Skin
174.88
87.61
70.53
54.30
43.21
27.36
Eye
147.95
74.12
59.67
45.94
36.56
24.3
Avg BFO
25.42
12.74
10.25
7.89
6.28
5.01
Stomach
9.60
4.81
3.87
2.98
2.37
2.17
Colon
21.03
10.54
8.48
6.53
5.20
4.27
Liver
14.61
7.32
5.89
4.54
3.61
3.06
Lung
17.29
8.66
6.97
5.37
4.27
3.6
Esophagus
16.44
8.24
6.63
5.11
4.06
3.44
Bladder
10.06
5.04
4.06
3.12
2.49
2.22
Thyroid
27.67
13.86
11.16
8.59
6.84
5.46
Chest
123.78
62.01
49.92
38.43
30.58
20.61
Gonads
58.92
29.52
23.76
18.29
14.56
10.28
Front Brain
46.69
23.39
18.83
14.50
11.54
8.76
Mid brain
23.50
11.77
9.48
7.30
5.81
4.81
Rear brain
45.59
22.84
18.39
14.16
11.27
8.58
Effective dose
48.25
24.17
19.46
14.98
11.92
6.18
Latest Updates: Color Coding Feature • Color coding of Rover after modifications gave much more control and visibility: – Feature allows for: • Using up to 100,000 rays • setting the range of values for which color coding will be applied (in this case the range of interest is between 4 g/cm2 to 15 g/cm2 of aluminum equivalent thickness) • Setting the number of colors to be divided linearly over the range, with red representing min to show hot spots • All values larger than max will be colored as max (yellow) and all values smaller than min will be colored as min (red)
Latest Updates to Fishbowl Tool Kit
15 g/cm2
11.33 g/cm2
7.67 g/cm2
4 g/cm2
Summary- Part I • We have developed a software tool for ray tracing that has the following capabilities: – Ray tracing multiple part, multiple material geometries – Up to 100,000 rays – Color coding the geometry exterior showing hotspots in design which can help in applications beyond radiation
• Tool was used to: – analyze lunar topography shielding effects – optimize the weight, size, and material of lunar rover prototype – calculate the directional shielding properties of such cases to assess the risk to humans in case of 1972 SPE
Optimized Design of Future Martian Transport Vehicles (MTV)
Vehicle Design – Material: Aluminum and water – Structure: 1- Cylindrical shell that includes main cabin and air lock 2- Racks (20 racks-16 racks in main cabin and 4 in air lock) 3- Water shield in the form of cylindrical blanket behind the shell.
Vehicle Design Cont.
• Thickness: Aluminum shell = 4g/cm2 Aluminum Racks= two layers (2.7 g/cm2 and 1.3 g/cm2) Water shield = 3 g/cm2
• Mass: Aluminum shell = 6,000 Kg Aluminum Racks= 500 Kg per rack (10,000 Kg for 20 racks) Water shield = 2,000 Kg
Ray Tracing (Dose Points)
locations of dose points inside MTV that were used in ray tracing
Hot Spots Detection Capabilities Single dose point Color Coding
Every ray is color coded according to the areal density value-Shielding- it provides. Only one dose point at a time-multiple colors
Hot Spots Detection Capabilities Multiple dose point Hotspot detection
Every ray that provides less than 10 g/cm2 shows up as a red pixel on the MTV surface. Multiple dose points-single color
Hot Spots Detection Capability Initial design
Initial Design: Hotspots are shown on sides of habitat.
Optimization Using Hot Spots Detection Capability Keeping the total mass constant: Initial design
First iteration change
Hotspots after first iteration
First iteration: - airlock internal wall thickness was reduced and a door was placed on the end point side of the racks. -Airlock racks were moved closer to working area
Optimization Using Hot Spots Detection Capability Keeping the total mass constant: First iteration change
Second iteration change
Hotspots after second iteration
Second iteration: - Another door was placed on the other end of racks.
Shielding Distribution at different Dose Points (Before and After Optimization) Shielding Distribution Comparison at End Point
Shielding Distribution Comparison at Mid Point
80
80
60 End Point
40
End Point_Optimized
XAl, g/cm2
100
XAl, g/cm2
100
20
Mid Point
40
Mid Point_Optimized 20
0 0
0
128 256 384 512 640 768 896 1024
0
Ray Number
100 80 60 Sleep Quarter 40
Sleep Quarter_Optimized 20
0 0
128
256
384
512
128
256
384
512
640
768
Ray Number
Shielding Distribution Comparison at Sleep Quarter
XAl, g/cm2
60
640
Ray Number
768
896
1024
896 1024
Point Dose Comparison of MTV Configuration - August 1972 Ground Level Enhanced (GLE) SPE 1200
Dose Equivalent, mSv
1000
800
Original
600
Optimized 400
200
0 End Point
Mid Point
Sleep Quarter
Effective Dose Comparison of MTV Configuration - August 1972 GLE SPE -
Effective Dose Equivalent, mSv
100
80
60 Original
Optimized
40
20
0 End Point
Mid Point
Sleep Quarter
Dose Equivalent at End Point of MTV Exposed to August 1972 GLE SPE 450 400
Dose Euivalent, mSv
350
300 250 200
Original Optimized
150 100 50 0
Dose Equivalent at Mid Point of MTV Exposed to August 1972 GLE SPE 140 120
Dose Equivalent, mSv
100 80 60
Original Optimized
40
20 0
Dose Equivalent at Sleep Quarter of MTV Exposed to August 1972 GLE SPE 100 90
Dose Equivalent, mSv
80
70 60 50 Original 40
30 20 10 0
Optimized
Summary and Future Work • Space Radiation Ray Tracing Tool demonstrated the ability to assess space habitat shielding and to locate and visually present weak shielding areas in the spacecraft allowing for iterative optimization of vehicle design. • Predictive software capability was used to optimize future Martian Transport Vehicle (MTV) prototype design and calculate risks to humans inside it. • Results showed that shield effect is improved for point dose and effective dose by 7 and 3 times, respectively, near the end of the optimized craft. • Future work to focus on ray tracing for Forward/Backward transport code with multiple material layouts
