Preliminary analyses have been performed of meteoroid impacts on lunar surface structures built with elements made from in situ materials. The SPHC hydrodynamic code was used to simulate impacts, and was validated against hypervelocity impact test results. Impact risk will affect necessary wall thicknesses, depth of burial, and placement of lunar base structures

Engler, Erich

Evans, Steven W.

Robinson, Jennifer

Stallworth, Roderick

Stellingwerf, Robert

NASA Technical Reports Server

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/NASA Marshall Space night Center 
Meteoroid Risk Assessment of Lunar Habitat Concepts 
Steven W. Evans', Roderick Stallworth2, Jennifer Robinson3, 
Robert Stellingwere, and Erich Engler5 
Mail Stop EM50, NASA Marshall Space Flight Center, Huntsville, AL 35812. 
2Mail Stop EV23, NASA Marshall Space Flight Center, Huntsville, AL 35812. 
Jacobs-Sverdrup, Huntsville, AL 358 12. 
4Stellingwerf Consulting, Huntsville, AL 35803 
'APL, NASA Marshall Space Flight Center, Huntsville, AL 35812 
1 
3 
Abstract 
Preliminary analyses have been performed of meteoroid impacts on lunar 
surface structures built with elements made from in situ materials. The SPHC 
hydrodynamic code was used to simulate impacts, and was validated against 
hypervelocity impact test results. Impact risk will affect necessary wall thicknesses, 
depth of burial, and placement of lunar base structures. 
Introduction 
Lunar habitat concept development and fabrication methods are being studied 
to hrther the manned exploration of space. The design of these structures will 
depend on the harsh environments they must withstand and the materials available for 
use. In order to achieve cost-, mass-, and volume-savings, it will be necessary to use 
in situ resources. Surface manufacturing and construction processes will dictate the 
structural elements to be used and the maturity of the overall design. In situ resources 
and materials will also be used to provide impact shielding for the habitat structure 
from meteoroids and lunar surface ejecta. It is imperative to include the effects of 
these impacts early in the program development to assess weight, schedule, and cost 
effects, and to allow integration of shielding requirements with other structural 
requirements. 
The purpose of this study was to evaluate some design concepts and analyze 
the impact phenomena expected from the meteoroid and ejecta models, including 
simulations of high velocity impacts. Required shielding and damage to habitats 
placed on the lunar surface were examined, along with the risk of various failure 
modes due to impacts. 
Potential Failure Modes 
The potential failure modes caused by hypervelocity impacts are thermal and 
radiation protection degradation; structural degradation by partial or complete wall 
penetration or by internal spallation; and injury to personnel. Several analysis 
methods have been employed to evaluate these effects. 
I 
I 
https://ntrs.nasa.gov/search.jsp?R=20060024733 2019-08-29T22:00:11+00:00Z
SPHC Impact Simulations 
- 
The Smooth Particle Hydrodynamics impact simulation code (SPHC) was 
used to examine penetration and fiacture of walls following impact. Code validation 
is an important part of this activity, and will continue as test data becomes available. 
Examples of some SPHC results on 1-foot-thick concrete models are shown in Figure 
1, and damage estimation curves developed fiom these simulations are shown in 
Figure 2. 
~- , . --------I -- -- 
Damage Depth = 9.42 &?diu.+' 
/ .. .
,./' I 
,I, '  2' 
r' 
Meteoroid Impact on a 1 Foot Thick Concrete Slab 
Impactor = sphere at V=20 luids, density = 0.5, stony. 
Blue nieaiw damaged material. 
3D model (cut) 
Particle Radius = 1 inch 
Particle Radius = 0.25 cm p.50 cm. 
. .  
1.0 cin 2.0 cin 
Radlut(cm) 
Figure 1. Examples of SPHC concrete impacts. 
Meteoroid Impact on R 1 Foot Thick Concrete Slab 
Impactor = sphere at V=20 hds, density = 0.5, stony. 
Particle Radius = 4.0 cin 
. <t :*> i . "  . 
6 1500 
0 00 
Figure 2. Sample damage estimation curves. 
A hemispherical concrete-walled dome structure having a diameter of 30 feet 
and a wall thickness of 2 feet is shown in Figure 3, as modeled by SPHC. A 1-bar 
atmosphere is modeled to show effects such as pressure loss and pressure pulse after 
wall perforation. The moon’s gravity is also modeled. The impactor is a 20 cm 
diameter, 2.1 kg, porous stoney meteoroid, striking at 20 km/sec. 
Figure 3. Dome structure impact simulation. 
The left figure shows the particle just before wall impact. The middle and 
right figures show the impact damage and depth of penetration into the wall during 
the impact process. The dark blue fractured material is surrounded by a light blue 
plastic wave traveling around the hemispherical dome. Although this model does not 
indicate immediate wall perforation, late time effects are likely to cause wall failure. 
Example Risk Assessment 
Estimated critical particle sizes from SPHC and from traditional penetration 
equations were combined with existing meteoroid and surface ejecta environment 
models to determine the risk of failures from various modes for the baseline mission 
parameters. 
The meteoroid and lunar surface ejecta environments were obtained from 
NASA SP-8013. Using this data, a set of curves for various mission lifetimes was 
generated from standard penetration equations for aluminum. These preliminary 
curves were used to formulate the analytical methodology. Figure 4 shows the curves 
for meteoroid assessments. 
Historically, initial design requirements for NASA missions have been set at a 
95% Probability of No Critical Failure (PNCF) for impacts. A shield design concept 
for the dome area could be determined as required by this number, to prevent critical 
damage to possible habitat elements such as windows or antennae. 
Alternative Habitat Concept Assessment 
An alternative lunar habitat consisting of a cylindrical structure 30 feet high, 
with a diameter of 26 feet, is shown in Figure 5 (Meyers, 2005). The exterior area of 
such a structure that is exposed to meteors is about 330 m2. The proposed wall 
thickness is 6 inches of processed regolith. The survivability of such a structure with 
respect to particle impact was estimated using an analytical approach consisting of the 
above meteoroid flux model, lunar ejecta flux model, and penetration results derived 
from a series of SPHC models of particle impacts on concrete blocks. 
I 
Parameter Curves to Aid in the Selection of Mission Design Requirements for 
Lunar Surface Meteoroid and Lunar Surface Ejecta Environinents 
Meteoroid 
Environment 
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Prellmlnary Ebtlmates 
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Tlus IS Uie paticle iilitss the design iiiiist witlistand to tlie critical diunage level desued. to iiieet the PNI selected 
To Detennine the Depth of Perietratioiioi Ciata Dainap of the Mass Fouiid in@. 
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dainage desniytioii can be ievised to sliow coinylete wall penetiatim hole diaineta. etc .to best iepiesalt the 
critical claiiiage to each system) 
Figure 4. Design curve for meteoroid assessments. 
Several models in the SPHC sequence used to examine damage to a six-inch 
concrete wall are shown in Figure 6.  All of the models simulated meteoroid impacts 
with velocity 20 km/s and density 0.5 g/cc (stony meteoroids). The radii of the 
particles used are shown in the figure. The crater depths of the models are well 
represented (R2 = 0.990) by the following fit to the data: 
D = 4.34 * d 
where D is the crater depth in cm and d is the particle diameter in cm. 
In order to include the ejecta damage (which occurs at a much lower velocity), 
additional models were run at velocities of 100 m/s to 20 km/s, for several densities 
of particle. The following fit represents the full data set with an R2 = 0.997: 
where D is crater depth in cm, p is projectile density in g/cm3, Vis projectile velocity 
in km/s, and r is projectile radius in cm. 
Figure 5. Alternative lunar habitat concept. 
Radius = 0.125 cm Radius 0.25 cm 
. .  
Radius = 0.50 cm Radius 0.75 cm 
Figure 6. Four SPHC models in the sequence of 6-inch-thick concrete walls. 
Figure 7 shows the Probability of No Penetration (PNP) for a concrete lunar 
structure with an external area of 330 m2, for a period of 20 years. The X-axis is the 
wall thickness; the left curve shows the ejecta result, while the right curve shows the 
meteoroid result. This is considered to be a conservative estimate of the survivability 
of the structure, considering solid particle impacts. The concrete wall is considered 
“penetrated” when the penetration depth exceeds 1/3 of the total thickness of the wall. 
At this point the concrete wall is likely to be severely damaged, with secondary 
damage (cracking) possibly extending through the entire wall. The PNP for ejecta is 
0.9999, while that due to meteoroids is 0.99, giving an overall PNP of 0.99. For 
meteoroids the critical case has a mass of 0.15 g and a diameter of 0.83 cm. For the 
ejecta the critical case has a mass of 6 kg and a diameter of 16.8 cm. 
differences are primarily due to the differing impact speeds. 
These 
1 
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Thickness (cm) 
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Figure 7. Probability of No Penetration (PNP) for meteoroids (right curve) and 
surface ejecta (left) versus wall thickness for concrete structures. 
Hypewelocity Impact Test Results 
A hypervelocity impact test was conducted, having as its target a 5x5x5-cm 
sample of sulfbr concrete. This item consisted of JSC-1 Lunar Regolith Simulant 
(65%) and sulfbr (35%). The sample was placed in the MSFC Impact Test Facility’s 
Micro Light Gas Gun’ target chamber, and was struck by a 1-mm diameter (-1.4e-03 
g) aluminum projectile at 5.85 km/s. Figure 8 shows a photo of the sample after the 
impact. A rather conical crater was produced in the target face measuring 12.8 mm in 
average diameter (6.4 mm radius) and 3.1 mm in central depth. Surrounding the 
crater is a zone of fractured material, which appears as a crenate cracked area - 8 - 12 
mm from the crater center, covering - 140 degrees, and exhibiting an attached flake 
and two scars fkom detached flakes, each - 3 - 4 mm long and 2 mm wide. 
Figure 9 shows the results of a simulation of this impact. The simulation crater 
is - 15 mm in diameter and 3.5 mm deep - in good agreement with the test crater 
dimensions - and shows a similar conical profile. Note the fractures (dark blue) 
extending about 1 cm into the sample below the crater. Grid lines are every 0.4 cm. 
Fig1 
projectile at 5.85 k d s .  
mum 
Figure 9. 
-z ".. 0 2 
x 
koss section of an SPHC model of the experimental shot. 
Conclusions 
For the 30-foot-tall silo structure considered here, the probability of serious 
impact damage over a 20 year interval is found to be about 1%. If ten of these 
structures were built to form a lunar base, the probability of wall penetration of one of 
the structures would increase to about lo%, an unacceptable level for manned 
structures. These are preliminary results, and a more detailed analysis will be needed 
for each candidate design. This result does clearly show, however, the importance of 
a meteoroid threat analysis for any fixed surface base on the moon, and the need to 
design the structures with this threat in mind. In particular, the identification of 
important or vulnerable areas on the structure could strongly affect the final result. 
Most meteor impacts with be from micrometeoroids. Although not a direct 
threat to the walls of a structure, vital communications equipment, external sensors, 
solar power generators, thermal radiators, etc., will be more sensitive to small 
impacts. Over time, erosion of tougher structures will occur. Impact models can be 
used to evaluate these types of effects. 
Another consideration is the effect of a large meteor impact on or near the 
lunar base. Large impacts do occur every day on the moon, and even though the 
probability of a nearby strike is very small, it could happen. Some warning might be 
available if a large impactor is dangerously near; in any case, a plan for evacuation to 
shelter, erection of a temporary shield, or relocation of the crew to a safer location 
should be developed in case of a catastrophic impact. A detailed analysis of the 
damage caused by such an event could help constrain the size, shape, and placement 
of individual structures in the base to minimize detrimental effects. 
Only a single experimental test has been done on simulated regolith material. 
Although the models of impacts on concrete agree reasonably well with this test, 
more data on a variety of lunar construction materials are needed. Once fully 
validated on several candidate materials, hydrodynamic models can predict damage at 
realistic velocities not attainable by experiments (20 km/s, vs. experiments at 7 km/s). 
The models can also be used in the design stage to evaluate the relative survivability 
of different structures. 
References 
Meyers, C., internal structural design memorandum to Marshall Space Flight Center 
In-situ Resource Utilization Project Office, Summer 2005. 
NASA SP-8013, “Meteoroid Environment Model: Near Earth to Lunar Surface,” 
1969. 


Meteoroid Risk Assessment of Lunar Habitat Concepts

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