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As humans endeavor to expand exploration of the final frontier in t...
In-Situ resource utilization (ISRU) is a term used predominantly ...
Launching a rocket from Earth to Mars on a successful trajectory is...
The first unmanned mission is scheduled to depart in the year 2020 ...
The International Space Station is equipped with a Water Recovery S...
Water electrolysis occurs when a water molecule is split into separ...
Regolith refers to the surface layer of martian soil that is compos...
A system like the Mars Atmospheric Resource Recovery System (MARRS)...
Through the dissolution of martian regolith in sulfuric acid, metal...
Using the Mars In-Situ Water Extractor (MISWE), liquid water is pro...
The thyroid gland requires iodide in order to synthesize the hormon...
The Sample Analysis on Mars instrument (SAM) has tools that enable ...
An auger based extraction system would consist of a drill with a he...
Life Sciences in Space Research 7 (2015) 57–60
Contents lists available at ScienceDirect
Life Sciences in Space Research
www.elsevier.com/locate/lssr
Water extraction on Mars for an expanding human colony
M. Ralphs
a,
, B. Franz
b
, T. Baker
c
, S. Howe
d
a
Utah State University, Logan, UT 84321, USA
b
University of Southern California, Los Angeles, CA 90089, USA
c
Idaho State University, Pocatello, ID 83201, USA
d
Howe Industries LLC, Idaho Falls, ID 83401, USA
a r t i c l e i n f o a b s t r a c t
Article history:
Received
25 August 2015
Received
in revised form 11 September
2015
Accepted
1 October 2015
Keywords:
Human
colony on Mars
Water
extraction
In-situ
resource utilization
Water
resources on Mars
In-situ water extraction is necessary for an extended human presence on Mars. This study looks at the
water requirements of an expanding human colony on Mars and the general systems needed to supply
that water from the martian atmosphere and regolith. The proposed combination of systems in order
to supply the necessary water includes a system similar to Honeybee Robotics’ Mobile In-Situ Water
Extractor (MISWE) that uses convection, a system similar to MISWE but that directs microwave energy
down a borehole, a greenhouse or hothouse type system, and a system similar to the Mars Atmospheric
Resource Recovery System (MARRS). It is demonstrated that a large water extraction system that can
take advantage of large deposits of water ice at site specific locations is necessary to keep up with the
demands of a growing colony.
© 2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.
1. Introduction
The ability to extract and process water through in-situ re-
source
utilization (ISRU) is necessary for a sustained human pres-
ence
on Mars. This study looks at the required hardware and the
related production rates that would be needed for water produc-
tion
for an expanding human colony on Mars. This colony would
receive new colonists from Earth every two years, when the plan-
ets
are positioned properly in their orbit and conditions are feasi-
ble
to send a mission to Mars (A propitious alignment of planets,
2015).
Although
not available in 2015, it is expected that future tech-
nology
will allow for missions to Mars to carry 6, 12, and eventu-
ally
24 humans in each mission, or that multiple transports will be
sent in each mission. With this assumption in mind, the planned
colony expansion is shown in Table 1.
The
amount of water needed for extended human survival is
around 0.6 kg/hr/person which includes water for consumption,
hygiene, and everyday living in space (Bobe et al., 2007; Horneck
et al., 2003, 2006). This estimate is based on space station living
and, assuming water consumption is less in a micro-gravity en-
vironment,
would increase up to 0.7 kg/hr/person to account for
living with gravity. The amount required if demands from a grow-
*
Corresponding author.
E-mail
addresses: miralphs@gmail.com (M. Ralphs), bfranz@usc.edu (B. Franz),
tedb314@gmail.com (T. Baker), steve@howeindustries.net (S. Howe).
Table 1
Planne
d
colony expansion, including crew size and colony population at any given
year in the first 16 years of the colony.
Year Mission # New crew Colony population
01 6 6
22 6 12
43 6 18
6 4 12 30
8 5 12 42
10 6 12 54
12 7 24 78
14 8 24 102
16 9 24 126
ing colony (regolith processing, manufacturing, perchlorate remedi-
ation,
plant growth, habitat maintenance, etc.) are added to human
needs is estimated at 1.2 kg/hr/person. Assuming a water recla-
mation
rate of at least 90% (similar to that of the space stations
Salut, Mir, and the International Space Station, Bobe et al., 2007;
Wieland,
1998), the amount needed from ISRU is 0.12 kg/hr/per-
son.
Some sources predict water reclamation rates as high as 96%
(Horneck et al., 2006), but current technology reliably allows for
90%.
These
numbers also take into account the requirements for
hydrogen since hydrogen will most likely come from water elec-
trolysis.
This is because most of the accessible hydrogen on Mars
is found in the form of H
2
O (Krasnopolsky and Feldman, 2001;
Boynton
et al., 2002).
http://dx.doi.org/10.1016/j.lssr.2015.10.001
2214-5524/
© 2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.
58 M. Ralphs et al. / Life Sciences in Space Research 7 (2015) 57–60
Some water can be extracted from the martian atmosphere, but,
in order to get enough to sustain a colony, extraction from the
martian regolith will be the primary source of water. Several meth-
ods
of water extraction from the regolith are considered viable and
the extraction method will depend heavily on the site selected for
the colony.
2. Colony water requirements
Water is needed for many applications for an extended colony
on Mars beyond the 0.6 kg/hr/person to keep the humans alive
and healthy. These applications fall into 5 categories: regolith pro-
cessing,
manufacturing, perchlorate remediation, plant growth, and
habitat maintenance.
2.1. Regolith processing
Many useful compounds exist in the martian regolith in sig-
nificant quantities
including silica, alumina, iron oxide, magnesia,
calcium oxide, and sulfates (Meyer, 1989; Stoker et al., 1993). The
metallic oxides can be extracted by dissolution in sulfuric acid. To
separate them, the solution is slowly neutralized using magnesia
to selectively precipitate relatively pure oxide powders. These pow-
ders
can be further processed to produce metallic ores (Berggren et
al., 2009). This processing can require a significant volume of wa-
ter
on the order of hundreds of liters, but nearly all is reclaimed
during processing. The makeup volume of water is therefore con-
sidered
negligible.
2.2. Manufacturing
The regolith processing results in a number of useful materi-
als
including metallic iron powder, alumina, magnesia, silica, and
residual regolith. These can be used to manufacture spare parts,
structural members (Landis, 2009; Kirn et al., 2002), advanced ce-
ramics,
explosives (Dick et al., 1985), and cementitious products.
Cementitious products are extremely useful for creating radiation
shielding (Kirn et al., 2002), pathways, structures, and protective
barriers, but they require a substantial amount of water. Concrete
production requires approximately 0.4 kg
H
2
O
/kg
concrete
(Berggren
et al., 2009). Concrete production will most likely use the most
water out of all the manufactured materials because that water
isn’t easily reclaimed. And, although there may be more need for
manufactured products towards the early stages of the colony, the
amount required will be normalized to the amount of people in
the colony. The estimated water required for manufacturing pro-
cesses
is 0.04 kg/hr/person.
2.3. Perchlorate remediation
Several perchlorate compounds are found on Mars that can be
detrimental to human health. The perchlorate molecules are sim-
ilar
to iodine and block its receptors in the human body, caus-
ing
hormone deficiencies (Wolff, 1998; Mukhi and Patiño, 2007;
Davila
et al., 2013). Therefore, it is imperative that the perchlorates
are removed from all the materials that will be used by humans.
This process is estimated to require 0.1 kg/hr/person of water, how-
ever,
almost all of this water can be recycled and reused so the
amount that ISRU will need to make up is considered negligible.
2.4. Plant growth
Plants are the most likely long term solution for food in a
colony on Mars (Schulze-Makuch and Davies, 2010). And whether
they are grown in hydroponic or potted systems, the plants will
consume a certain amount of water. It is estimated that plants will
require approximately 0.003 kg/hr/person of water that cannot be
easily reclaimed by the environmental control and life support sys-
tems
(ECLSS). This must, therefore, be produced by ISRU.
2.5. Habitat maintenance
Water needed for habitat maintenance will vary depending on
the design of the habitat. A few uses of water that fall under
this category are increasing grounding pin efficiency, resupply of
fuel cells (Baird et al., 2003), and resupply of coolant in power
systems. The estimated requirement for habitat maintenance is ap-
proximately
0.01 kg/hr/person of water.
3. Water extraction from the atmosphere
The martian atmosphere is made up of 0.03% H
2
O (Muscatello
and Santiago-Maldonado, 2012). Using an atmospheric processing
system, similar to the Mars Atmospheric Resource Recovery System
(MARRS) (England, 2001), it is plausible to extract 0.02 kg/hr/per-
son
of water from the atmosphere. This amount relates to the wa-
ter
that would be extracted from the atmosphere during the pro-
cess
of extracting the required oxygen for breathable air (Wieland,
1998). This also neglects oxygen regeneration in the habitat which
would decrease the amount of water produced with this system.
This system will grow as needed to support the oxygen needs
of the growing colony. However, since this system will vary de-
pending
on the amount of oxygen regeneration in the habitat and
0.02 kg/hr/person is the maximum that would be produced, the
actual amount of water that would be produced is small and non-
constant.
Thus the atmosphere is not a good source for water to
sustain an expanding colony.
4. Water extraction from regolith
The water available for extraction from the martian regolith is
site dependent. At higher and lower latitudes, the majority of the
water is found in icy soils and permafrost. Around the equator,
most of the water content is found in hydrated minerals. There
is some speculation that more water exists deeper in the regolith
that may be available if a method is developed to drill down to
it (Clifford, 1993), but at present this solution is not proven. But
even near the equator where the water content is low, the re-
golith
is very hard and difficult to remove in large quantities. It
is estimated that a 2 ton excavator would be required to scoop up
regolith containing more than 5% water content in a 4.5 cm wide
scoop (Zacny et al., 2012a). However, advanced scooping systems
are
being developed for martian and lunar surfaces that are capa-
ble
of excavating a significant amount of regolith (Mueller et al.,
2013). The following excavation methods were chosen with the
hard martian regolith in mind and are considered some of the
most probable options for water extraction from the regolith.
4.1. Hydrated minerals
In the equatorial regions of Mars, the regolith is predicted to
contain between 2% and 13% water content, most likely in the form
of hydrated minerals (Muscatello and Santiago-Maldonado, 2012;
McKay
et al., 1993; Feldman et al., 2004). More energy is required
to release the water from hydrated minerals than to sublimate the
water from icy soils and permafrost. Although a few of the hy-
drated
minerals found in the martian regolith have dehydration
temperatures that are relatively low, as shown in Table 2, tem-
peratures
in excess of 600
Care typically required to remove all
the water from the hydrated minerals (Sanders and Mueller, 2015).
However, the Sample Analysis on Mars (SAM) instrument on the
Curiosity rover showed that a heating above 450
Ccauses the
M. Ralphs et al. / Life Sciences in Space Research 7 (2015) 57–60 59
Table 2
Hydrated
minerals that have a confirmed presence at several locations on the mar-
tian
surface. Also included is their chemical formula and dehydration temperatures.
Mineral Chemical formula Dehydration temp (K)
Kieserite MgSO
4
·H
2
O
Epsomite MgSO
4
·7H
2
O301
Gypsum CaSO
4
·2H
2
O1073
Melanterite FeSO
4
·7H
2
O 363
Analcime NaAlSi
2
O
6
·H
2
O 773
Mirabilite Na
2
SO
4
·10H
2
O306
Perchlorate M(ClO
4
)
2
·nH
2
O600
Opal-A SiO
4
·4H
2
O 973
carbonates and perchlorates in the regolith to break down and pro-
duce
HCl and H
2
S, which may not be desirable (Leshin et al., 2013).
Regardless, there are two methods of water extraction that look
most promising for removing water from hydrated minerals, both
use an auger based system, but one uses convective heat trans-
fer
and one uses microwave. An auger based system is considered
ideal because of its ability to penetrate the hard martian regolith
and actually move the soil (Zacny et al., 2008, 2012a, 2012b).
The
system that uses convective heat transfer would be a sys-
tem
similar in design to Honeybee Robotics Mobile In Situ Water
Extractor (MISWE) (Zacny et al., 2012a). This system uses an auger
to dig into the soil, lifts the soil caked on the auger back into the
rover, applies convective heat to evaporate the water into vapor,
and collects the water vapor in a cold trap to condense. This sys-
tem
is predicted to have a water extraction rate of 0.2 kg/hr and
would require around 350 Watts of thermal power for evaporating
the water and additional electrical power for operating the auger
and rover, for a total of around 1kW
e
.
The
system that uses microwave energy is similar to the con-
vective
system explained above, however, the auger would be used
to dig a bore hole into which microwave energy could be emit-
ted
with the intent of energizing a greater amount of water for
each hole drilled. The vaporized water could then be collected and
condensed in the rover. Microwave heating has the potential to
penetrate further into the regolith and heat the water molecules at
a faster rate than convection (Ethridge and Kaukler, 2012, 2011). It
is estimated that a borehole and microwave system would be able
to produce slightly more than a MISWE while using comparable
amounts of power: 0.3 kg/hr with 1kW
e
.
4.2. Icy soils
In icy soils, which are as low as 40
N latitude in some locations
(Byrne et al., 2009), the two auger based systems proposed would
most likely still be viable, but other methods might also be used
that have the potential of a higher extraction rate. These options
are in the form a greenhouse (Mungas et al., 2006)or a hothouse.
The difference between the two is the heat source: one is the Sun,
the other is from an external source. The concept is to heat up
the inside of a tent or dome on the surface of Mars over an area
with icy soil or permafrost. The water would evaporate out and
condense on the walls of the structure to be collected.
Using
the energy from the Sun would be very beneficial, how-
ever,
there are some complications with that method, which in-
clude,
but are not limited to: the transparent material to be used
on the structure, keeping the dust off the surface of the structure,
and solar interference from frequent dust storms. Using an exter-
nal
heat source, such as from a surface reactor or a battery, would
provide its own limitations. A few of the limitations may include
mobility and distance from the main base, which may limit the
accessible soils that can be tapped for water extraction. But if the
challenges for either system can be overcome, then a system such
as this would be able to provide a much greater quantity of water
Table 3
Proposed
configuration for water extraction on Mars for an expanding human
colony. “Col.” = total number of humans in the colony, “Goal” = water produc-
tion
goal in kg/hr, “MISWE” = number of MISWE’s, “B.M.” = number of bore-
hole/microwave
systems, “H.H.” = number of hothouse or greenhouse systems,
“Prod.” = water produced by the proposed configuration in kg/hr. “Prod.” includes
0.02 kg/hr/person from a system similar to the MARRS system. It is assumed that
MISWE and B.M. are extracting water from hydrated minerals with between 5 and
7% water content and the H.H. is extracting water from icy soils and permafrost.
Col. Goal MISWE B.M. H.H. Prod.
60.74 2 2 0 1.21
12 1
.48 2 2 0 1.33
18 2
.21 2 2 1 3.44
30 3
.69 2 2 1 3.68
42 5
.17 4 4 1 5
54 6
.64 4 4 2 7.24
78 9
.59 4 4 3 9.7
102 12
.55 6 6 4 13.26
126 15
.56 6 5 15.71
150 15
.56 6 5 15.71
Fig. 1. Water required for the expanding colony as well as the amount produced by
the proposed configuration.
for the colony. A larger, high production water extraction system is
crucial for an expanding human colony on Mars.
5. Growth with the colony
In order for the water extraction to grow with the colony, the
proposed configuration of water extraction methods is shown in
Table 3. This configuration assumes that methods are available to
store the excess water produced for several years as a reserve.
These numbers correspond to the total colony needs, including
human consumption and hygiene, habitat requirements, manufac-
turing
processes, and plant growth. The ability of this system to
keep up with an expanding colony on Mars over time can be visu-
alized
by Fig. 1. If a large scale water production system, like the
hothouse, is not available, it would require 65 MISWE’s to accom-
modate
a colony of 126 humans.
6. Conclusions
With an expanding human colony on Mars, the primary source
of water is going to come from the regolith. Therefore, a system
will need to be developed that can take advantage of larger water
sources (such as water ice) near the site selected for the colony.
Acknowledgements
Thanks to the Universities Space Research Association and the
Center
for Space Nuclear Research for funding this research.
60 M. Ralphs et al. / Life Sciences in Space Research 7 (2015) 57–60
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