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Additive manufacturing (AM) is one of the most promising techniques for on-site manufacturing on extraterrestrial bodies. In this investigation, layerwise solar sintering under ambient and vacuum conditions targeting lunar exploration and a moon base was studied. A solar simulator was used in order to enable AM of interlockable building elements out of JSC-2A lunar regolith simulant. Solar additively manufactured samples were characterized mechanically regarding their compressive and bending properties. Moreover, samples were analyzed morphologically using X-ray tomography and scanning electron microscopy (SEM) followed by density measurements. AM for identical process parameters led to final products with different physical and chemical characteristics when performed under ambient and vacuum conditions. Hence, process parameters were optimized under each individual working atmosphere. The experimental data were further integrated into finite-element (FE) calculations. This led to the refinement of the design of interlocking building elements for lunar applications. These blocks have the potential to form structures for shielding a pressurized inflatable habitat from radiation and micrometeorite impacts or creating nonpressurized shelters for robotic machinery.
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Solar Sintering for Lunar Additive Manufacturing
Miranda Fateri, Ph.D.1; Alexandre Meurisse, Ph.D.2; Matthias Sperl, Ph.D.3;
Diego Urbina4; Hemanth Kumar Madakashira5; Shashank Govindaraj6;
Jeremi Gancet, Ph.D.7; Barbara Imhof, Ph.D.8; Waltraut Hoheneder9;
René Waclavicek10; Clemens Preisinger, Ph.D.11; Emilio Podreka, Ph.D.12;
Makthoum Peer Mohamed13; and Peter Weiss, Ph.D.14
Abstract: Additive manufacturing (AM) is one of the most promising techniques for on-site manufacturing on extraterrestrial bodies. In this
investigation, layerwise solar sintering under ambient and vacuum conditions targeting lunar exploration and a moon base was studied.
A solar simulator was used in order to enable AM of interlockable building elements out of JSC-2A lunar regolith simulant. Solar additively
manufactured samples were characterized mechanically regarding their compressive and bending properties. Moreover, samples were an-
alyzed morphologically using X-ray tomography and scanning electron microscopy (SEM) followed by density measurements. AM for
identical process parameters led to final products with different physical and chemical characteristics when performed under ambient
and vacuum conditions. Hence, process parameters were optimized under each individual working atmosphere. The experimental data were
further integrated into finite-element (FE) calculations. This led to the refinement of the design of interlocking building elements for lunar
applications. These blocks have the potential to form structures for shielding a pressurized inflatable habitat from radiation and microme-
teorite impacts or creating nonpressurized shelters for robotic machinery. DOI: 10.1061/(ASCE)AS.1943-5525.0001093.© 2019 American
Society of Civil Engineers.
Author keywords: Additive manufacturing; Interlocking building elements; Solar sintering; Moon.
Introduction
A return to the Moon is now part of the Global Exploration
Roadmap with robotic missions planned for the years between
2020 and 2025 (ISECG 2018). Following the landers and rovers,
human missions are being contemplated and a permanent lunar
base could be envisaged. This vision, named Moon Village by the
European Space Agency Director General (ESA DG) Jan Wörner,
would be an outpost where international astronauts would perform
scientific experiments and prepare for exploration and settlement
on more distant planetary bodies (Stenzel et al. 2018).
However, planning a long-term crewed lunar mission is expen-
sive and risky. To solve these issues, in situ resource utilization
(ISRU) was developed, whereby lunar soil can be used for volatile
extraction (Schwandt et al. 2012) or can be exploited to construct
roads or shelters for protecting crews from space radiation and
meteorite impacts (Cesaretti et al. 2014).
Following the ISRU, an additive manufacturing (AM) approach
for freeform geometry fabrication is among the appropriate can-
didates for on-site manufacturing. Currently, researchers are in-
vestigating feasibility of the layerwise shaping of lunar soil using
different bonding and binding mechanisms. At a small scale, selec-
tive laser sintering/melting (SLS/SLM) and selective inhibition
sintering (SIS) have shown promising results (Krishna Balla et al.
2012;Khoshnevis et al. 2014;Fateri and Gebhardt 2015). The fea-
sibility of microwave sintering is also among the current investiga-
tions (Fateri et al. 2019a).
For larger scale construction, contour crafting (CC) and binder
bonding (D-shape) technologies have been conceptually proven
(Cesaretti et al. 2014;Khoshnevis et al. 2012), but the use of a
binder makes these two concepts reliant on Earth supplies. Taking
into consideration the full potential of available resources on the
Moon, using sunlight and lunar dust (direct sintering/no use of
binder), could be the most feasible on-site manufacturing approach.
1Research Fellow, Institut für Materialphysik im Weltraum, Deutsches
Zentrum für Luft- und Raumfahrt, Köln 51170, Germany (corresponding
author). Email: miranda.fateri@gmail.com
2Research Fellow, Institut für Materialphysik im Weltraum, Deutsches
Zentrum für Luft- und Raumfahrt, Köln 51170, Germany. ORCID: https://
orcid.org/0000-0001-8955-6926
3Professor, Institut für Materialphysik im Weltraum, Deutsches
Zentrum für Luft- und Raumfahrt, Köln 51170, Germany.
4Team Lead, Future Projects and Exploration, Space Applications
Services, Leuvensesteenweg 325, Zaventem, Brussel 1932, Belgium.
5Systems Engineer, Future Projects and Exploration, Space Applica-
tions Services, Leuvensesteenweg 325, Zaventem, Brussel 1932, Belgium.
6Team Leader, Robotics Software, Space Applications Services,
Leuvensesteenweg 325, Zaventem, Brussel 1932, Belgium.
7Division Manager, Technologies, Applications and Research, Space
Applications Services, Leuvensesteenweg 325, Zaventem, Brussel 1932,
Belgium.
8Team Lead, LIQUIFER Systems Group, Obere Donaustraße
97-99/1/62, Vienna 1020, Austria. ORCID: https://orcid.org/0000-0001
-5968-1929
9Design Engineer, LIQUIFER Systems Group, Obere Donaustraße
97-99/1/62, Vienna 1020, Austria.
10Design Engineer, LIQUIFER Systems Group, Obere Donaustraße
97-99/1/62, Vienna 1020, Austria.
11Senior Engineer, Bollinger und Grohmann GmbH, Franz-Josefs-Kai
31/1/4, Frankfurt am Main 60327, Germany.
12Senior Engineer, Bollinger und Grohmann GmbH, Franz-Josefs-Kai
31/1/44, Frankfurt am Main 60327, Germany.
13Aerospace Engineer, Compagnie Maritime dExpertise, 36 Blvd.
de lOcéan, Marseille 13009, France.
14Team Lead, Compagnie Maritime dExpertise, 36 Blvd. de lOcéan,
Marseille 13009, France.
Note. This manuscript was submitted on November 21, 2018; approved
on June 21, 2019; published online on September 14, 2019. Discussion
period open until February 14, 2020; separate discussions must be sub-
mitted for individual papers. This paper is part of the Journal of Aerospace
Engineering, © ASCE, ISSN 0893-1321.
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Solar sintering has first shown its use for dust mitigation purposes,
roughly sintering the top layer of lunar regolith with sunlight con-
centrated by a Fresnel lens (Hintze et al. 2009). However, a more
recent work from the European Space Agency-General Support
Technology Programme (ESA-GSTP) study (Meurisse et al. 2018)
has shown the feasibility of manufacturing of basic geometries
such as bricks by mirror-based concentrators and solar sintering.
In this study, interlocking building elements from lunar regolith
simulant were manufactured layer-by-layer using solar sintering,
targeting the technology readiness level (TRL) 4 under ambient
conditions and TRL 5 under vacuum conditions. Fabricated geom-
etries were analyzed to determine their morphology and mechanical
properties. The obtained material properties were evaluated for
lunar construction considering the lunar environment.
Ultimately, a mission scenario was developed based on the
experimental and finite-element method (FEM) analysis. The mis-
sion scenario was designed based on interlocking building elements
(Dyskina et al. 2005), which would cover an inflatable habitat with-
out the utilization of scaffolding. The mission scenario provided a
larger picture including the steps required to build a habitat on the
lunar surface.
Material
Abundant materials on the Moon are divided in two categories
of anorthositic (Highlands) rocks and basaltic (Maria) rocks. In
this study, JSC-2A material [supplied from Zybek Advanced
Products (ZAP)] was used as the test material representing a mare
regolith containing low titanium content. JSC-2A is a replica
simulant of JSC-1A, a widely studied simulant (Taylor et al.
2016) initially developed by National Aeronautics and Space
Administration (NASA) using mined volcanic sediments in
Arizona. JSC-1A used to be supplied by Orbital Technologies
Corporation (ORBITEC); however, it is not commercially available
anymore. Therefore, JSC-2A material was chosen as the test
material for solar sintering investigations in this study. SEM image
of JSC-2A simulant is shown in Fig. 1. It can be seen that the
particles have irregular shapes and a polydisperse grain size distri-
bution ranging from a few micrometers to 1 mm. For the experi-
ments, JSC-2A simulant was used as received with no additional
sieving process.
The chemical composition of JSC-2A is reported by ZAP to
be similar to JSC-1A. JSC-1A contains different minerals such
as pyroxene (augite, diopside, enstatite, and hedenbergite), plagio-
clase (anorthite and albite), olivine (fayalite and forsterite), and
other oxides (ilmenite, magnetite, and hematite). Mineralogy stud-
ies on this simulant are reported by Gustafson and Owens (2006)
and Meurisse et al. (2017).
The nominal chemical composition of JSC-1A/JSC-2A is
shown in Table 1. Further information on the melting behavior
of JSC-2A, including the indicated minerals for AM application,
can be found in a recent published study (Fateri et al. 2019b).
Methodology
For the experiments, two AM setups were developed for solar
sintering capable of functioning under ambient and vacuum con-
ditions. Initial experiments were conducted under ambient condi-
tions. The vacuum AM setup was designed accordingly based on
the obtained results of initial ambient sintering.
Ambient Solar Sintering AM Setup
Initial experiments for AM under ambient conditions were
conducted using two Xenon lamps (power, 6 kW; wavelength,
380780 nm; manufacturer, OSRAM, Regensburg, Germany) sim-
ulating the solar light. Irradiated light from Xenon lamps was con-
centrated in a parabolic mirror and projected onto a water-cooled
mirror in order to change the beam orientation from horizontal to
vertical [Fig. 2(a)]. Powder was deposited in a layerwise manner us-
ing a feeder assembly based on an array of three Auger screws in a
row and a set of custom-designed spreaders installed on top of a
stainless steel vibrating ramp with adjustable inclination [Fig. 2(b)].
For the experiments an inclination angle of 60° was found to be
optimum in order to deliver a homogenous layer of regolith (the
optimum steep angle was found empirically).
The spreaders were placed directly below each of the screws in
order to obtain a more homogeneous spread of material over the
ramp. The mechanism had an adjustable powder delivery mass flow
rate ranging from 4.2 to 10.8g=s of JSC-2A simulant. Delivering a
mass flow of approximately 5g=s led to layer thickness of 100 μm.
These values were obtained empirically. Once the regolith was
spread on the tray, a pressing operation was performed to compact
the freshly deposited layer. This was done using a stamper (an alu-
minium plate attached to four adjustable springs) placed below
the feeding box. Furthermore, using a three-dimensional (3D)-axis
table, generation of sliced geometry profiles was enabled. The
maximum print volume was set to 250 ×150 ×100 mm. Position-
ing and fine-tuning the irradiation of AM setup and the Xenon
lamps resulted in a 12 mm diameter spot and a flux density of
1,200 kW=m2at the focal point. A porous alumina-based ceramic
Fig. 1. SEM image of JSC-2A particles.
Table 1. Chemical composition of JSC-1A/JSC-2A
Oxide % by weight
SiO246.67
Al2O315.79
CaO 9.90
MgO 9.39
FeO 7.57
Fe2O33.41
Na2O 2.83
TiO21.71
K2O 0.78
MnO 0.19
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plate with a porosity of ranging from 1 to 5 mm in size was used as
the build platform. Fig. 3shows the measured Gaussian distribution
of the concentrated Xenon light.
Vacuum Solar Sintering AM Setup
The ambient print setup design was redesigned and another setup
implemented for carrying out experiments under vacuum condi-
tions. For vacuum sintering (Fig. 4), a vacuum chamber with a
diameter of 600 mm and height of 374 mm was used. The vacuum
AM prototype comprised a three-axis table providing precise
translation in the XYZ-directions. The printer stages, along with
their stepper motors, were certified to operate under the vacuum
environment, and the respective motors had a maximum operating
temperature of 65°C, requiring water cooling at key locations of
the table and a thermal fabric (Hiltex alumina-silica) insulating the
stages. A feeder of reduced size was developed to suit the vacuum
chamber. Because custom designed spreaders could not fit in the
vacuum chamber, the AM setup under vacuum included five auger
screws to spread the regolith more homogenously. Due to the lim-
itations of the available vacuum chamber, the stamping step was
removed for vacuum printing.
For AM under vacuum, the chamber was evacuated approxi-
mately for an hour before the printing started. Once the pressure
dropped below 150 mbar, the AM process was initiated. The po-
tential dusty environment in the chamber after the sintering began
prevented the use of a turbo-molecular pump to reach a higher vac-
uum level. The gas pressure within the chamber initially increased
rapidly to over 200 mbar. Following this, the pressure increased
linearly, at a rate of approximately 2.3mbar=s until the end of
the process. The pressure evolution graph during the AM process
is shown in Fig. 5.
Fig. 2. (a) AM setup for ambient sintering; and (b) the powder feeding system.
Fig. 3. Flux density of the concentrated sunlight at the solar simulator.
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Design of Interlocking Building Elements
Interlocking building elements were designed using Rhino and
Grasshopper software packages. A range of geometries for the
construction of main infrastructure components of a lunar base
were developed by considering the following applications:
Radiation shielding for inhabited and pressurized modules;
Nonpressurized shelters as dust and micrometeoroid protection
for machinery;
Launch pad apron to prevent dust spreading too far toward the
lunar base; and
Terrain modeling for a radio telescope on the far side of
the Moon.
Following different approaches in parallel, several element types
were developed, which could be categorized as follows:
Elements with three-dimensional interlocking capacities, such
as (1) 3D formfitting stackable (e.g., derived from Platonic geo-
metries, comb-shaped) [Fig. 6(a)]; and (2) 3D randomly packed
aggregates [Fig. 6(b)].
Elements with 2.5-dimensional interlocking capacities, namely
those formfitted for curved and self-supporting vault construc-
tion elements [Fig. 6(c)].
Elements with two-dimensional (2D) interlocking capacities,
specifically flat ground stabilizing elements for surface battle-
ment [Fig. 6(d)].
Interlocking Building Element Selected for AM under
Ambient and Vacuum Conditions
From the developed geometries, the tetrahedron-based geometry
was chosen for AM under ambient conditions. The chosen ele-
ments center mass [Fig. 6(d)] remains within the contact area
ground projection during the construction phase, while following
the appropriate stacking sequence. The center of mass of the dome
segment is kept inside its footprint. The aim was to allow the erec-
tion of dome structures without the need of scaffolding during
construction.
The results of initial sintering under ambient conditions
(Meurisse et al. 2018) showed that the concentrated light beam
diameter of 12 mm was too large to accommodate the necessary
resolution for a tetrahedron-based element with acute angles
and building volume of 250 ×150 ×100 mm. Therefore, it was
decided to develop an amended geometry, avoiding sharp angles.
For AM under vacuum, because the chamber had a limited volume,
a flat element (volume of 120 ×170 ×15 mm) was selected
(Fig. 6).
Analysis of the Additively Manufactured Parts
The solar sintered objects were cut to obtain sample sizes used for
compression and bending tests. For compression tests the cut sam-
ples were 20 ×20 ×20 mm 2mm and covered with mortar, en-
suring flat and even surfaces in contact with the universal testing
machine. For the bending tests, cut samples 10 ×10 ×40 mm were
tested parallel to the layers and cut samples 10 ×20 ×70 mm used
for perpendicular tests. Two different universal testing machines
were used in this study. Compression tests were performed with
a PEZ 1595 and bending tests were carried out with a three-point
apparatus on an Instron 5543A machine. On both machines, the
stroke was set to 0.5mm=min.
SEM analysis was performed using a Zeiss LEO 1530 VP with
an energy-dispersive X-ray (EDX) system by Oxford Instruments.
Densities of sintered samples were measured using an envelope
density analyzer Micromeritic GeoPyc 1360. X-ray tomography
was performed using a Nanotom-Phoenix X-ray machine. From
the mechanical tests, the mean value and standard deviation of com-
pressive and tensile bending strength were determined providing
design values for these properties. The applied procedure for cal-
culating design properties was based on Eurocode EN1990 (CEN
1990) and made use of the semiprobabilistic safety concept. The
design values for loads and material properties were determined
such that the overall structure had an acceptable probability of fail-
ure during its lifetime. For determining the design values of sintered
regolith a failure probability of 105was chosen.
Results
AM of Parts under the Ambient Condition
For initial trials, several test geometries were additively manufac-
tured as shown in Fig. 7. A light flux density of 1.2MW=m2, a scan
speed of 47 mm=s, and a layer thickness of 100 μm were found
to be the optimum process parameters for printing under ambient
Fig. 5. Pressure evolution during the AM under vacuum.
Fig. 4. (a) Integrated vacuum setup in solar oven; (b) vacuum printer
before adding shielding cover; and (c) after adding shielding cover.
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conditions. The hatch distance (distance between scanned lines)
was varied between 10 and 20 mm according to the geometry
and the available path for the three-axis table. Presented parts in
Fig. 7were fabricated using 400 stacked layers. The triangle
and S-shaped part had their 2D cross sections repeated over the
whole process. Fig. 7shows parts that were successfully manufac-
tured; however, desired dimensional accuracy of the final objects
was not achievable due to the limited resolution of the concentrated
Xenon light beam. Following these, fabricated parts underwent
manual postprocessing in which 6 mm of semiadhered particles
to the parts walls were removed.
AM of Parts under the Vacuum Condition
Initial testing for AM under vacuum was conducted using the same
process parameters as for solar sintering in air following a prede-
fined path. As shown in Fig. 8(b), due to the lack of air convection
under the vacuum, the layers were completely molten. The process
parameters were modified to avoid this. The lamps intensities were
lowered to provide approximately 1MW=m2and the scanning
speed was increased to 65 mm=s. Using the modified parameters,
sintered layers with macroscopically similar characteristics to those
of the parts manufactured under ambient conditions was achieved
[Fig. 8(c)]. The printed geometry was approximately 1 mm thick,
and thus brittle.
As such the mechanical analysis of the parts under vacuum
was not feasible. (further trials in order to build more robust struc-
tures under vacuum are in the scope of future studies). However, a
microscopic observation was performed using X-ray tomography
and SEM.
Mechanical Tests and Microscopic Observations
Averages of the compressive strength and Youngs modulus (E)of
tested geometries manufactured under ambient condition are given
in Table 2, while the flexural strength average is given in Table 3.
Additively solar sintered regolith was observed to have mechanical
properties close to gypsum.
Fig. 7. Computer designed models and respective solar sintered parts.
Fig. 6. Geometries of interlocking building elements from (a) 3D formfitting stackable elements; (b) 3D randomly packed aggregates;
(c) 2.5-dimensional elements formfitted for curved and self-supporting vault construction; (d) 2D flat ground stabilizing elements for surface battle-
ment; and (e) 2.5-dimensional elements formfitted for curved and self-supporting vault construction.
Fig. 8. Additive manufactured parts under vacuum: (a) CAD drawing; (b) first vacuum printing trial using the ambient process parameters; and (c) the
trial using the modified process parameters.
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AM solar parts resulted in similar mechanical properties when
compared to the AM laser sintered components (Goulas et al.
2018) with a maximum compressive strength of 4.20.1MPa and
elastic modulus of 0.287.36.6GPa. Mechanical analysis of the
vacuum sintered parts was not feasible due to the limited size of
manufactured parts.
X-ray tomography reconstructions of the AM solar sintered
parts under ambient and vacuum condition are shown in Fig. 9.
AM vacuum sintered parts exhibited a foamy structure, containing
more porosity compared to the ambient AM solar sintered parts.
The foamy structure could be explained by the outgassing of the
grains while being partially molten. However, the pore formations
origin in this process need to be studied in more detail. So far there
are only a few studies reporting the same phenomenon when ex-
posing the lunar simulant to the heat (Goulas et al. 2017;Song
et al. 2019).
AM solar sintered parts under ambient condition contained
closed pores (mostly spherically shaped) up to 0.4 mm in diameter
and open pores (mostly irregular in shape, interconnected channels
of pores) up to 0.5 mm in length. Numerous closed pores larger
than 0.4 mm in diameter were clearly visible through X-ray tomog-
raphy of vacuum AM sintered parts. The swollen pores break the
bridges formed between weakly attached grains, thus forming open
pores up to 1.5 mm in length.
SEM results from ambient and vacuum solar sintered samples
are shown Fig. 10. SEM back-scattered images of additive manu-
factured parts under different working atmospheres confirm the
foamy structure seen by tomography analysis of vacuum sintered
parts. SEM of the samples revealed the structure formation was due
to outgassing of the material trapped between the partially molten
grains, thus creating numerous closed and open pores. Energy dis-
persive X-ray analysis revealed a matrix of olivine and pyroxene
embedded in plagioclase grains. It is conluded that plagioclase
minerals can be observed as part of the grains of sintered samples
in both air and vacuum.
Results regarding the density measurements of JSC-2A in pow-
der form and as additive manufactured parts are shown in Table 4.
Results showed that additive manufactured solar sintered parts
exhibited densities of 1.70 and 1.21 g=cm3under ambient and
vacuum conditions, respectively. Vacuum sintered parts yielded a
density lower than the powder bulk density, which confirms the
presence of bubbles and the aforementioned foam structure. Pore
formation of vacuum sintered regolith simulant was also reported
Table 2. Results of compression tests on solar sintered JSC-2A regolith
simulant
Parameter Average of 23 samples
Compressive strength (MPa) 2.49
Standard deviation (MPa) 0.71
Youngs modulus (GPa) 0.21
Standard deviation (GPa) 0.15
Table 3. Results of bending tests on solar sintered JSC-2A regolith
simulant
Test
Flexural
strength
(MPa)
Standard
deviation
(MPa)
Average of 28 samples tested
parallel to the layers plane
0.55 0.36
Average of eight samples tested
perpendicularly to the layers plane
0.23 0.10
Fig. 9. X-ray tomography of AM solar sintered samples under (a) air;
and (b) vacuum conditions.
Fig. 10. SEM back-scattered image of AM solar sintered regolith in
(a) air; and (b) vacuum in different magnifications.
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by Song et al. (2019) where ambient and vacuum sintered parts
presented densities of above and below 50% of the regoliths skel-
etal (true density, 2.92 g=cm3), respectively.
Structural Design
Sintered regolith behaves similarly to unreinforced concrete. The
ratio of the mean value of tensile to compressive strength is roughly
1:5. However, the tensile strength shows a much larger variation
(defined as the ratio between standard deviation and mean value)
than the compressive strength. Thus the safety margin for the ten-
sile strength needs to be larger than that of the compressive strength
in order to achieve the same level of reliability. The structural ex-
periment results suggest the primary difficulty in structure design
utilizing AM solar sintered parts is the relative low tensile strength
of the regolith blocks. Therefore, the geometry of structures should
be chosen such that, under the governing external loads, predomi-
nantly compressive stresses result. One investigated method that
could be applied to achieve this was the hanging model approach
following a catenary line. In this study an elastic membrane with
zero bending stiffness, which initially spans horizontally between
lines where the final structure meets the ground, is loaded perpen-
dicularly to its plane in an upward direction. The resulting deflected
shape is primarily in tension. When the load is reversed it acts in the
direction of gravity and causes the stresses in the structure to
change from tension to compression.
Structures that serve as shelters need to have a cross section
height of roughly 3 m so that they provide sufficient shielding
against radiation and micrometeorites. This makes dead weight
and moonquakes the governing external loads. The acceleration
of gravity on the Moon amounts to 1.62 m=s2, for moonquakes
a maximum horizontal acceleration of 0.25 m=s2was assumed.
Based on these, loads assemblies of interlocking brick elements
were structurally analyzed. The geometry of the structures was de-
rived using the hanging model approach. The sintered regolith
bricks and the contact conditions between the bricks were structur-
ally idealized as beam elements. The connections between the
bricks were modeled as compression only elements in order to
allow for gaps opening due to external loads. Fig. 11 shows the
beam elements that idealize the bricks; on the left side the connec-
tion elements are shown. The rectangles associated to each element
indicate tension or compression. Fig. 11 shows that there are no
tensile contact forces under dead weight and moonquake in the fi-
nal structure. Except for two elements near the supports also the
internal brick forces are compression only. This shows that the
given geometry can be built from sintered regolith bricks without
the use of an additional binder.
Scenarios, Building Process, and Applications
Solar additive manufacturing technology can be applied in lunar
missions for construction of shelters suitable for inhabitation
and protecting machinery. The scenario presented in this paper
is generic and might suit any international roadmap. The scenario
steps for making solar AM infrastructure possible are as follows.
Solar AM will use three different specialist robots to construct
the lunar infrastructures. The surveying robots arrive first and will
initiate the excavation and sintering process. Robotic infrastructure
to fulfill these tasks could use cableway systems or autonomous
rovers depending on the mission requirements and on the distance
between the regolith excavation site and the lunar base. After ex-
cavating, the regolith could be sintered and the element delivered
for construction. The excavation robots have a refinery unit at-
tached so only the suitable regolith would be sintered. Finally, after
the elements have been sintered, the robots collect the interlocking
building elements and position them into the desired building
envelope. Depending on the scale of the interlocking element these
robots will either be crane type rovers for placing large scale build-
ing blocks or paving machine types for placing multiple building
blocks in a uniform pattern (Fig. 12).
From the published data (Meurisse et al. 2018) it is known that a
brick of an approximate size 15 ×5×30 cm takes 30 min to print
through solar sintering in an ambient environment, resulting in a
printing time of 222 h=m3. An assumed habitable dome structure
with an internal diameter of 20 m and an interior height of 8 m
would require approximately 3,400 elements of averaged 0.5m3
each, resulting in a total structure volume of 1,700 m3.
A nonhomogenous cross section composed of loose sand
material embedded and capsuled by a rigid additive manufactured
structure would substantially reduce the required manufacturing ef-
fort. The required interior additive manufactured structure may be
reduced down to 30% of the total volume (Fig. 13). Taking this into
account, it would require six printers to build one habitable dome
structure per year.
Table 4. Density measurements of JSC-2A in powder form and as solar
sintered parts
Parameter Value (g=cm3)
Powder bulk density 1.56
Skeletal density 2.92
Ambient solar sintered part density 1.70
Vacuum solar sintered part density 1.21
Fig. 11. Compressive normal forces in final structure with contact elements under tension removed. The stability of the remaining structure proves the
viability of assembling structures from element with compression-only connections.
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The radiation requirements are based on Benaroyas investiga-
tions, which extensively and in detail studied the construction op-
tions for the Moon. It appears that at least 2.5 m of regolith cover
would be required to keep the annual dose of radiation at 5 roentgen
equivalent man (REM)/(5 centiSv), which is the allowable level for
radiation workers (0.5 REM for the general public) (Benaroya 2002).
Following the initial definition of the mission architecture ele-
ments for a lunar base, the following elements were chosen for the
lunar solar additive manufacturing application:
Habitats should be built with a reusable inflatable mold and
a pressurized volume comprised of inflatable and hard shell
connectors;
Shelters (nonpressurized storage spaces) for equipment and
machinery should provide protection from micrometeoroids;
Launch pads should consist of leveled terrain with an apron to
avoid spreading of lunar dust toward the base; and
Telescopes for the far side of the Moon require terrain leveling
within a suitable crater.
A building sequence for dome structures based on the dodeca-
hedron spacefiller geometry is shown in Figs. 14 and 15.
Conclusion
AM of JSC-2A using solar sintering (artificial sunlight-Xenon
lamps) was investigated in this study. Interlockable elements were
successfully manufactured under ambient conditions using a lamp
intensity of 1.2MW=m2, a scanning speed of 47 mm=s, a layer
thickness of 100 μm, a hatch distance of approximately 15 and
12 mm diameter focal spot. When the ambient process parameters
were applied to a vacuum sintering environment, molten-deformed
layers with a foamy, porous, and brittle structure were formed. The
process parameters were subsequently modified to a lamp intensity
of 1MW=m2and a scanning speed of 65 mm=s achieving macro-
scopically sintered parts.
Solar sintering of the regolith simulant under ambient conditions
resulted in additive manufactured parts with a compressive strength
of 2.49 MPa and a Youngs modulus of 0.21 GPa while parts cre-
ated under vacuum did not fulfill the geometry requirements for
mechanical testing. Layerwise solar sintered samples exhibited a
density of 1.70 and 1.21 g=cm3under ambient and vacuum con-
ditions, respectively.
The geometric limitations observed due to beam focus and
material constraints lead to several recommendations for the struc-
tural design approach. Elements should be compact and designed
with beveled edges and obtuse angles. The elements should be
surveyed following sintering to ensure they satisfy geometric
constraints necessary for use in a building.
Fig. 13. Dodecahedron interlocking building element with inner struc-
ture filled with lunar regolith.
Fig. 12. Scenario for building and assembly: (a) sintering robots; (b) collection robots; (c) transportation and assembly robots; and (d) artistic
visualizations.
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Structuralanalysis using FEM showed that specificgeometries can
be built from the solar sinteredregolith (considering the lunar gravity)
without the use of any additional binder material. These geom-
etries were designed to minimize or eliminate tension in the structure.
It is concluded that, for primary buildings, solar sintering could
be used to provide shielding against the lunar environment and
terrain modeling for external facilities. Investigation of melting
behavior of the lunar regolith under reduced gravity and vacuum
conditions is within the future scope of this study.
Acknowledgments
Project RegoLight has received funding from the European Unions
Horizon 2020 research and innovation program under Grant
Agreement No. 686202. The authors wish to thank Martin Thelen,
Christian Willsch, Christian Raeder, Hans-Gerd Dibowski, Joseph
Salini, Matthias Kolbe, Olfa Lopez, Anthony Rawson, and Valerie
Morisseaux for their support during the test campaigns in
Deutsches Zentrum für Luft- und Raumfahrt (DLR)-Cologne.
References
Benaroya, H. 2002. An overview of lunar base structures: Past and future.
In Proc., AIAA Space Architecture Symp. Reston, VA: American
Institute of Aeronautics and Astronautics.
CEN (European Committee for Standardization). 2002. EurocodeBasis
of structural design. EN 1990. Brussels, Belgium: CEN.
Cesaretti, G., E. Dini, X. Kestelier, V. Colla, and L. Pambaguian. 2014.
Building components for an outpost on the lunar soil by means of
Fig. 14. Building sequence for dome structures based on the dodecahedron spacefiller geometry.
Fig. 15. Pressurized module configuration, transparent view.
© ASCE 04019101-9 J. Aerosp. Eng.
J. Aerosp. Eng., 2019, 32(6): 04019101
Downloaded from ascelibrary.org by Miranda Fateri on 09/15/19. Copyright ASCE. For personal use only; all rights reserved.
a novel 3D printing technology.Acta Astronaut. 93 (Jan): 430450.
https://doi.org/10.1016/j.actaastro.2013.07.034.
Dyskina, A. V., Y. Estrinb, E. Pasternaka, H. C. Khora, and A. J. Kanel-
Belov. 2005. The principle of topological interlocking in extraterres-
trial construction.Acta Astronautica 57 (1): 1021. https://doi.org/10
.1016/j.actaastro.2004.12.005.
Fateri, M., A. Cowley, M. Kolbe, O. Garcia, M. Sperl, and S. Cristoforetti.
2019a. Localised microwave thermal post-treatment 1 of sintered sam-
ples of lunar simulant.J. Aerosp. Eng. 32 (4): 0001039. https://doi.org
/10.1061/(ASCE)AS.1943-5525.0001039.
Fateri, M., and A. Gebhardt. 2015. Process parameters development
of selective laser melting of lunar regolith for on-site manufacturing
applications.Int. J. Appl. Ceram. Technol. 12 (1): 4652. https://doi
.org/10.1111/ijac.12326.
Fateri, M., S. Pitikaris, and M. Sperl. 2019b. Investigation on wetting and
melting behavior of lunar regolith.Microgravity Sci. Technol. 31 (2):
161167. https://doi.org/10.1007/s12217-019-9674-5.
Goulas, A., J. G. Binner, D. S. Engstrøm, R. A. Harris, and R. J. Friel.
2018. Mechanical behaviour of additively manufactured lunar regolith
simulant components.Proc. Inst. Mech. Eng. Part L: J. Mater. Des.
Appl. https://doi.org/10.1177/1464420718777932.
Goulas, A., J. G. Binner, R. A. Harris, and R. J. Friel. 2017. Assessing
extraterrestrial regolith material simulants for in-situ resource utilisation
based 3D printing.Appl. Mater. Today 6 (Mar): 5461. https://doi.org
/10.1016/j.apmt.2016.11.004.
Gustafson, M., and C. Owens. 2006. Characterization summary of
JSC-1AF lunar mare regolith simulant.In Proc., NIST Particle Work-
shop. Washington, DC: National Aeronautics and Space Administration.
Hintze, P., J. Curran, and T. Back. 2009. Lunar surface stabilization via
sintering or the use of heat cured polymers.In Proc., 47th AIAA
Aerospace Sciences Meeting Including the New Horizons Forum and
Aerospace Exposition. Reston, VA: American Institute of Aeronautics
and Astronautics.
ISECG (International Space Exploration Coordination Group). 2018. The
global exploration roadmap. 3rd ed. Washington, DC: ISECG.
Khoshnevis, B., A. Carlson, N. Leach, and M. Thangavelu. 2012.
Contour crafting simulation plan for lunar settlement infrastructure
buildup.In Proc., Earth and Space 2012: Engineering, Science, Con-
struction, and Operations in Challenging Environments, 14581467.
Washington, DC: National Aeronautics and Space Administration.
Khoshnevis, B., J. Zhang, M. Fateri, and Z. Xiao. 2014. Ceramics 3D
printing by selective inhibition sintering.In Proc., Solid Free Form
Symp. (SFF). Austin, TX: Solid Free Form.
Krishna Balla, V., L. B. Roberson, G. W. OConnor, S. Trigwell, S. Bose,
and A. Bandyopadhyay. 2012. First demonstration on direct laser fab-
rication of lunar regolith parts.Rapid Prototyping J. 18 (6): 451457.
https://doi.org/10.1108/13552541211271992.
Meurisse, A., J. C. Beltzung, M. Kolbe, A. Cowley, and M. Sperl.
2017. Influence of mineral composition on sintering lunar regolith.
J. Aerosp. Eng. 30 (4): 04017014. https://doi.org/10.1061/(ASCE)AS
.1943-5525.0000721.
Meurisse, A., A. Makaya, C. Willsch, and M. Sperl. 2018. Solar 3D print-
ing of lunar regolith.Acta Astronaut. 152 (Nov): 800810. https://doi
.org/10.1016/j.actaastro.2018.06.063.
Schwandt, C., J. A. Hamilton, D. J. Fray, and I. A. Crawford. 2012.
The production of oxygen and metal from lunar regolith.Planet.
Space Sci. 74 (1): 4956. https://doi.org/10.1016/j.pss.2012.06.011.
Song, L., J. Xu, S. Fan, H. Tang, X. Li, J. Liu, and X. Duan. 2019.
Vacuum sintered lunar regolith simulant: Pore-forming and thermal
conductivity.Ceram. Int. 45 (3): 36273633. https://doi.org/10.1016/j
.ceramint.2018.11.023.
Stenzel, C., L. Weiss, and T. Rohr. 2018. Sustainable challenges on the
moon.Curr. Opin. Green Sustainable Chem. 9 (Feb): 812. https://doi
.org/10.1016/j.cogsc.2017.10.002.
Taylor, L. A., C. M. Pieters, and D. Britt. 2016. Evaluations of lunar re-
golith simulants.Planet. Space Sci. 126 (Jul): 17. https://doi.org/10
.1016/j.pss.2016.04.005.
© ASCE 04019101-10 J. Aerosp. Eng.
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