58 M. Ralphs et al. / Life Sciences in Space Resear ch 7 (2015) 57–60

Some wate r can be extra cte d fr om the martian atmosphere, but,

in order to get enough to sustain a colon y, extr action from the

martian regoli th will be the primary source of wate r. Sev eral meth-

ods

of wate r extr action from the regol ith are consider ed viable and

the extr action method will depend heavil y on the site selected for

the colony .

2. Colony wa te r requirement s

Wa t e r is need ed fo r man y applications for an exte nd e d colony

on Mars bey ond the 0.6 kg/hr/person to keep the humans alive

and health y . These applications fa ll into 5 categ ories: rego lit h pro-

cessing,

manufacturing, perc hlorate r emediation, plant growth, and

habitat maintenance.

2. 1 . Re gol it h processing

Man y useful compounds ex i st in the martian re goli th in sig-

niﬁcant q uantities

including silica, alumina, iron ox i de , magnesia,

calcium ox i d e, and sulfates ( Meyer , 1989; Stoker et al., 1993 ). The

metallic ox i de s can be ext rac te d by dissolution in sulfuric acid. To

separate them, the solution is slowly neutralized using magnesia

to selectiv ely precipitat e relative ly pure ox i d e po wders. These pow-

ders

can be further pr ocessed to produce metallic ores ( Berggren et

al., 2009 ). This processing can require a signiﬁcant volu me of wa -

ter

on the order of hundreds of liters, but nearl y all is rec lai med

during processing. The makeup vo lum e of wa te r is therefore con-

sidered

negligible.

2.2. Manufacturing

The re goli th processing res ults in a number of useful materi-

als

including metallic iron powder , alumina, magnesia, silica, and

residual rego li th. These can be used to manufacture spare parts,

struc tural members ( Landis, 2009; Kirn et al., 2002 ), advanced ce-

rami cs ,

explosiv es ( Dick et al., 1985 ), and cementitious products.

Cementitious products are extr emely useful for creating radia ti on

shielding ( Kirn et al., 2002 ), pathway s, st ruct ures, and pro tecti ve

barriers, but they re quire a substantial amount of wa te r. Concrete

production require s approximat ely 0.4 kg

H

2

O

/kg

concrete

( Berggren

et al., 2009 ). Concrete production will most likely use the most

wat er out of all the manufactured materials because that wa te r

isn’t easily reclaimed. And, although there may be more need for

manufactured products toward s the early sta ges of the colon y , the

amount requi red will be normalize d to the amount of people in

the colony . The estimated wate r requi red for manufacturing pro-

cesses

is 0.04 kg/hr/person.

2.3. Perchlor ate remediation

Sever al perchlor ate compounds are found on Mars that can be

detrimental to human health. The perc hlorate molecules are sim-

ilar

to iodine and block its r eceptors in the human body , caus-

ing

hormone deﬁciencies ( Wo l f f , 1998; Mukhi and Pat iño, 2007;

Davila

et al., 2013 ). Theref ore, it is imperati ve that the perchlor ates

are remove d from all the materials that will be used by humans.

This process is estimated to require 0. 1 kg/hr/person of wat er, how -

ever ,

almost all of this wa te r can be recycled and re use d so the

amount that ISRU will need to make up is considered negligible.

2.4. Plant growth

Plants are the most likely long te rm solution for food in a

colon y on Mars ( Schulze-Makuch and Davies, 2010 ). And whether

they are grown in hydr oponic or potted systems, the plants will

consume a certain amount of wat er. It is estimated that plants will

require appro ximately 0.003 kg/hr/person of wate r that cannot be

easily reclai me d by the envir onmental contr ol and lif e support sy s-

tems

(ECL SS). This must, therefore, be produced by ISRU .

2.5. Habitat maintenance

Wa t e r needed for habitat maintenance will var y depending on

the design of the habitat. A few uses of wat er that fa ll under

this category are increasing grounding pin eﬃciency , resupply of

fuel cells ( Baird et al., 2003 ), and resupply of coolant in power

syst ems. The estimated req uirement for habitat maintenance is ap-

pro ximately

0.01 kg/hr/person of wat er.

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

syst em, similar to the Mars A tmospheric Resou rc e Rec over y Sy stem

(MARRS) ( England, 2001 ), it is plausible to ex tra ct 0.02 kg/hr/per -

son

of wa te r from the atmosphere. This amount re late s to the wa -

ter

that woul d be ext ra cte d from the atmosphere during the pro-

cess

of extracting the re quire d oxy ge n fo r breathable air ( Wieland,

1998 ). This also neglects ox yge n regen era tio n in the habitat which

wou ld decrease the amount of wat er produced with this system.

This system will grow as needed to support the ox yge n needs

of the gro wing colon y . Howev er , since this system will va r y de-

pending

on the amount of oxyg e n regen erat io n in the habitat and

0.02 kg/hr/person is the maximum that wou ld be produced, the

actual amount of wa te r that wo ul d be produced is small and non-

constant.

Thus the atmosphere is not a good source for wat er to

sustain an expanding colony .

4. Water extraction from regolith

The wat e r available fo r extraction from the martian re goli th is

site dependent. At higher and lower latitudes, the ma jority of the

wat er is found in icy soils and permafrost. Around the eq uator ,

most of the wa te r content is found in hy d ra t e d minerals. There

is some speculation that more wat er exi st s deeper in the regol ith

that may be av ailable 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 wa te r content is low , the re-

goli th

is ver y hard and diﬃcult to re move in large quantities. It

is estimated that a 2 ton excava tor wou ld be require d to scoop up

regol it h containing more than 5% wa te r content in a 4.5 cm wide

scoop ( Zacn y et al., 2012a ). How ever , advanced scooping syst ems

are

being developed for martian and lunar surfaces that are capa-

ble

of excava ti ng a signiﬁcant amount of rego lit h ( Mueller et al.,

2013 ). The following ex cavation methods were chosen with the

hard martian regoli th in mind and are considered some of the

most probable options for wa te r extraction from the re goli th.

4. 1 . Hydrated minerals

In the equatorial regions of Mars, the regol ith is predicted to

contain betw een 2% and 13% wat er content, most likel y in the form

of hy d ra t e d minerals ( Muscatello and Santiago-Maldonado, 2012;

McKay

et al., 1993; Feldman et al., 2004 ). More energy is requi red

to rele ase the wa te r from hy d r a te d minerals than to sublimate the

wat er from icy soils and permafros t. Although a few of the hy -

drated

minerals found in the martian regoli th have dehydr ation

temper atures that ar e re lat ively low , as shown in T able 2 , tem-

peratures

in exce ss of 600

◦

Ca r e typically re quire d to remove all

the wat er from the hyd ra t e d minerals ( Sanders and Mueller , 2015 ).

How ever , the Sample Analysis on Mars (SAM) instrument on the

Curiosity rover showed that a heating above 450

◦