POPULATION PLANNING FOR FUTURE SPACE COLONIES

M.B.N. Kouwenhoven,1 Don Eliseo Lucero-Prisno III,2 Xu Lin,3 Jiangchuan He,4 and Wei Hao5

1Department of Mathematical Sciences, Xi’an Jiaotong-Liverpool University, 111 Ren’ai Rd., Suzhou Dushu Lake Science and

Education Innovation District, Suzhou Industrial Park, Suzhou 215123, P.R. China2Department of Global Health and Development, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine,

Keppel St., Bloomsbury, London WC1E 7HT, United Kingdom3Department of Thoracic Surgery, The First Affiliated Hospital, School of Medicine, Zhejiang University, 79 Qingchun Road,

Hangzhou, 310003, P.R. China4Department of Public Health, Karolinska Institutet, SE-171 77 Stockholm, Sweden

5Max-Planck-Institut fur Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany

ABSTRACT

The future of humanity may involve the establishment of permanent settlements on the Moon, on

Mars, or on large space stations. The technological and financial challenges associated with achieving

this goal are large, but these may be overcome if the economical, environmental, or political need

to settle in space becomes sufficiently large. The psychological, medical, and sociological constraints

establishing a space colony are far more challenging, and may even prevent humanity from reaching the

interplanetary age at all. In this study we investigate the demographic requirements and constraints

for a space colony during its initial hundred years, and the medical, psychological, and sociological

problems that may arise. We find that most of the straightforward population planning requirements

(steady migration, absence of enforced family planning, etc) frequently result in a colony that either

goes extinct, or evolves into a demographically unstable society (distorted population pyramids, gender

imbalances, etc). We explore the demands for physical and mental healthcare, and possible solutions to

the problems that arise from long and confined stays beyond planet Earth. A well-planned and highly

disciplined division of labour is particularly important for space colonies with small populations (less

than a hundred). Appropriately dealing with human needs (medical, psychological, and sociological) is

perhaps a far larger constraint than those imposed by technology and survival requirements; perhaps

it is even the limiting factor for the future exploration of space.

Keywords: population management, space settlements, migration, birth control, public health

1. INTRODUCTION

For the long-term survival of humanity, a cosmic di-

aspora is probably inevitable. A common argument is

that by establishing space colonies, humanity may be

able to prevent existential threats (e.g., Matheny 2007,

and references therein). We have already taken the first

steps through the establishments of small space sta-

tions and exploratory visits to the Moon. It is likely

that further endeavours in the near future will lead to

the establishments of space habitats that can be per-

manently inhabited by larger groups of settlers. Al-

Corresponding author: M.B.N. Kouwenhoven

t.kouwenhoven@xjtlu.edu.cn

though some author argue that the costs and risks of

establishing a permanent remote space colony are cur-

rently considered far too high to be realistic (e.g., Coates

1999; Slobodian 2015), circumstances may change in the

near future. The establishment for permanently inhab-

ited space colonies may be driven by a variety of con-

siderations, such as scientific exploration (see Spudis

1992), terraforming (e.g., Fogg 1998, and references

therein) territorial expansion by nation states (e.g., Mar-

shall 1995; Szocik et al. 2017), commercial activities un-

dertaken by governments or companies (e.g., Benaroya

2001; Metzger et al. 2012), or escape from a deterio-

rating living environment on Earth. These space habi-

tats can include large revolving space stations in orbit

around the Earth (e.g., O’Neill 1974), settlements on

the Moon (e.g., Mendell 1985), or settlements on Mars

2 Kouwenhoven, Lucero-Prisno, Lin, He & Hao

(e.g., Petrov 2004), or in the distant future perhaps even

interstellar arks (see, e.g., Marin 2017, 2018). Below,

we will collectively refer to such settlements as space

colonies. Each of the drivers for space colonisation as-

sociated limitations for communication, migration, and

access to resources, and each type of settlement has its

own advantages and disadvantages, primarily related to

the availability of materials, travel time for goods and

people, economic interests, communication, and health

risks.

The establishment and survival of such space colonies

is highly dependent on the available technology at that

time, including space travel technology, environmental

conditioning technology, acquiring and processing raw

materials, and available medical resources. Many of

these technologies are already available, at least theo-

retically (see, e.g., Mishkin & Lee 2007, and references

therein). It is, for example, already possible to con-

tinuously operate robotic rovers on the Moon and Mars

for a decade. Robotic missions are substantially cheaper

than human missions, robots are less limited by environ-

mental circumstances, and robots may be able to carry

out most mission objectives, such as exploration and

mining, without the physical presence of humans (e.g.,

Huntsberger et al. 2000; Schenker et al. 2003).

As mentioned above there are still good reasons to es-

tablish inhabited space colonies. Long-term settlement

in space, however, poses significant challenges, including

the provision of conditions necessary for survival (water,

oxygen, food, atmospheric properties), physical health

(radiation, exposure to low gravity), mental health (iso-

lation), transport (which may take up to years, in the

case of a Mars colony), and supply of goods. Even if

all these conditions for a healthy survival are met, so-

cietal imbalance can still endanger the survival of the

habitat. Such imbalances could include unsustainable

changes in the size of the population, substantial gen-

der imbalances, and populations that have a too large

fraction of the population that is in need of care (the

elderly, the sick, and children). These human condi-

tions are often overlooked or neglected. It is likely that

technological challenges will be solved well before the

population balance problem is solved.

In this report we investigate what measures should be

taken to establish a new space colony with a healthy

population balance. In Section 2 investigate the demo-

graphic constrains on a space colony, and we present the

tools and assumptions we use to model the evolution of

the population. In Section 3 we present our numerical

results, and identify under which conditions a healthy

population balance is obtained. In Section 4 we address

the medical and psychological conditions that may af-

fect small-population colonies, the societal impacts of

demographical imbalance, and the problems related to

the division of labour. Finally, we present and discuss

our conclusions in Section 5.

2. MODELLING POPULATION GROWTH

We carry out numerical simulations to model the evo-

lution of the population, and determine the constraints

that are necessary for a balanced evolution of the space

colony. Important parameters that determine the out-

come include the size of the initial population (the pio-

neers), the age distribution, the gender distribution, and

the migration rate. Below, we investigate the survival

chances for different scenarios.

2.1. Requirements for a healthy population balance

Let N(t) = Nm(t)+Nf (t) be the population of a space

colony at time t (in years), where Nm is the number of

number of males and Nf is the number of females. The

colony is established at t = 0 years and is evolved up to

time t = T = 100 years. Let ai be the age of each person

i. We define the young population as the inhabitants

with ai < 18 years, the workforce population as those

with 18 ≤ ai < 65 years, and the old population as those

with ai ≥ 65 years. Below, we refer to these as children,

workers, and elderly, respectively.

The population grows due to births and immigration,

and shrinks due to deaths. Long-term sustainability of

a space colony requires a fine-tuned population balance.

We set the following minimum demographic require-

ments for a healthy population balance that is needed

for survival of the space colony;

1. Over longer periods of time, the population should

grow: N(T ) > N(0).

2. Over shorter periods of time, the population

should not decrease drastically, i.e., not with more

than 10% within any period of 10 years or shorter:

(N(t+ ∆t)−N(t))(∆t)−1 > −10% for any period

∆t ≤ 10 years. This important limitation is re-

lated to the balance in the division of labour and

expertise amongst the inhabitants.

3. Over shorter periods of time, the population

should not increase drastically, i.e., not with more

than 50% within any period of 10 years or shorter:

(N(t + ∆t) − N(t))(∆t)−1 < 50% for any period

∆t ≤ 10 years. This constraint is necessary for

the colony to adjust itself under the conditions of

scarce resources.

4. The gender ratio should remain balanced to avoid

the adverse effects of a societal imbalance (e.g.,

Population planning for space colonies 3

Table 1. Initial number of inhabitants (pioneers) of thespace colony.

Pioneer team N Nm Nf

i 0 0 0

ii 20 10 10

iii 200 100 100

iv 4000 2000 2000

Table 2. Different scenarios for migration policy and familyplanning polity for the space colony.

Scenario am bm gm p0

A1 0 0 0.5 1

A2 0 0 0.5 2

A3 0 0 0.5 0.5

B1 − 20 0.1 − 2 0 0.5 1

C1 − 13 0.5 0 0.3 − 0.6 1

Xiaoyi et al. 2010; Kaur 2013), with a possi-

ble exception for the initial settlement phase:

Nm(t)/N(t) > 30% and Nf (t)/N(t) > 30% for

any time t > 10 years.

5. The number of unpartnered adult inhabitants (ex-

cluding widows/widowers) should remain limited,

i.e., below 30% for each gender at any time t >

10 years, as partnering can substantially bene-

fit mental health and societal stability (see, e.g.,

Adamczyk 2017; Maher 2018).

6. The proportion of the population that participates

in the workforce should remain above 50% at any

time, as this workforce is responsible for care of

the minors, the sick, and the elderly, in addition

to their core duties.

7. The fraction of children among the inhabitants

should remain below 30% at any time, in order

to limit the pressure of care and education on the

available labour resources in the colony, and to

avoid a highly-perturbed population pyramid at

later times.

2.2. Modelling the evolution of the population

We numerically investigate the evolution of the dif-

ferent population models, for different initial popula-

tions and for different policies. We start out simula-

tion at t = 0 years and adopt integration time steps of

∆t = 1 yr for a timespan of 100 years. Each simulation

is initialised with a group of pioneers that is present at

the colony when the simulation stars. This group of pi-

oneers consists of Nm(0) males and Nf (0) females, with

ages drawn from a Gaussian distribution N (35, 15) with

the additional constrain that all are adult. Over the

course of one year, the change in the population is

∆N = ∆B + ∆M −∆D (1)

The evolution of the population is modelled with the

following procedure.

(i) Death. Each inhabitant has an age-dependent

probability dm(a) (for males) and df (a) (for females) of

dying, where a is the age. Deceased inhabitants are re-

moved from the population. We age-specific death rates

from Arias et al. (2014). For these death rates, the me-

dian lifespan of a male and female inhabitant is then

af = 79 years and am = 83 years, respectively. The

total number of deaths in the colony in year t is then

∆D =

∫ amax

0

(Nf (a)df (a) +Nm(a)dm(a)) da (2)

where amax is the age of the oldest person in the colony.

(ii) Birth. Each year, partnered couples have a prob-

ability p0pb(a) of giving birth to a child, where a is the

age of the female. We adopt the age-specific birthrates,

pb(a), of Bohnert et al. (2015). We include a family plan-

ning factor p0 that can be use to enhance or decrease the

number of births, where p0 = 1 refers to uncontrolled

family planning. Over the course of a lifetime, the to-

tal fertility of the average female, if birth control is not

applied is then

Bf = p0

∫ a2

a1

pb(a)da (3)

where a1 is the age at which the female finds a partner,

and a2 the age at which the female or her partner dies.

In the optimal scenario (a1 = 18 years, a2 > 50 years),

a typical couple produces Bc = 2.17p0 children in their

life. In the absence of enforced population planning

(p0 = 1) this value is slightly higher than population

replacement value. The total number of children born

in the colony each year, ∆B, depends on the size of the

female population, the gender ratio, the age distribu-

tion, and the age-dependent partnering ratio.

(iii) Migration. Migrants arrive at the colony and are

added to the population. The number of migrants and

their age distribution varies in the different scenarios.

We adopt a zero emigration rate, as the main purpose of

the colony is to build up a permanent settlement. Each

year, a constant number of migrants, am arrives, plus

a fraction bm of the current population. Small values

of am ensure a smooth population growth during the

evolution of the colony. The annual number of migrants

added to the population is

∆M(N) = bam + bmN + εc . (4)

4 Kouwenhoven, Lucero-Prisno, Lin, He & Hao

Each year, the value of ∆M is rounded off down to the

closest integer, and the remainder, ε, is added to the next

year. As the colony grows (N � 1), the first term van-

ishes and ∆M ≈ bmN . Among the migrants, a fraction

gm is male and a fraction (1−gm) is female. The gender

ratio (which in the ideal case is gm = gf = 0.5) can be

adjusted to ensure a healthy population balance. The

age distribution of the migrants is drawn from a Gaus-

sian distribution N (35, 15) with the constraint that all

have ages of 18 years or above.

(iv) Partnering. Adult inhabitants that are unpart-

nered and were previously unpartnered, are assigned a

partner, provided that such a partner is available and

provided that the age difference between the potential

partners is ∆a ≤ 10 years. In the real world this is

not a policy but often a matter of personal choice (e.g.,

Goodwin et al. 2002).

(v) Ageing. Every year, the age of each inhabitant

increases by one year.

We carry out simulations with different initial condi-

tions. The properties of the initial population are listed

in Table 1. The different policy scenarios are listed in

Table 2. Due to the comparatively small number of in-

habitants, especially during the earliest stages of coloni-

sation, the evolution of the systems exhibits a large de-

gree of stochasticity. An ensemble of 100 simulations of

each scenario is therefore carried out to account for sta-

tistical fluctuations that occur particularly during the

initial development of the space colony.

3. POPULATION MODELS: APPLICATIONS

3.1. Pioneer-only scenario

We first consider the case where a large group of set-

tlers is sent out in one batch, without any subsequent

immigration. This scenario allow us quantify the impact

of the choice for the pioneer population on the future

evolution of the colony, and to address the properties

of a naturally-evolving population. This scenario may

occur when home planet is unwilling or unable to con-

tribute to the space colony after the initial settlement

has taken place.

The evolution of several isolated pioneer settlements

is shown in Figure 1. The fact that the group of pioneers

is not representative for the age distribution on Earth

has important impacts on the population during the first

century of the colony, notably several decades after ar-

rival. Small settlements are often unable to survive un-

der these conditions, even if they prevent inbreeding,

unless strict family planning policies are implemented

(see Figure 2). The pioneers cause a baby-boom upon

their arrival, and are responsible for a population of el-

derly inhabitants at 40 − 50 years after their arrival.

Figure 1. The evolution of isolated populations for modelsA1. Top: total population over time for models A1-ii (lowercurve), A1-iii, and A1-iv (upper curve). Bottom: the popu-lation categories. The region below the bottom curve repre-sents the fraction of minors, the middle region the fractionalworkforce, and the region above the upper curve representsthe fraction of elderly. Shaded regions indicate the standarddeviations for the ensemble of models.

Although the colony survives, a substantial drop in the

total population is seen at t = 70 year. The ∼ 20 year

age gap between the pioneers and the first generation

of children results in rapid fluctuations in the available

workforce, with only about 35% of the population avail-

able for carrying out work and to take care of the elderly

and children at time t = 50 years.

Stability is achieved after roughly a century. As the

natural growth rate (birthrate minus death rate) is close

to zero, the size of these population is stable, and grows

at an average rate of 1.3% per year. At the same time,

the gender ratio remains close to 0.5, and the fraction of

unpartnered inhabitants approaches zero, and the frac-

tions of children, workers, and elderly remain constant

at 22%, 58%, and 20%, respectively. After several gen-

erations, the fraction of the population available for the

Population planning for space colonies 5

Figure 2. A realisation of model A1-ii, in which a population of twenty inhabitants is sent to a space colony, and no furthermigration occurs. Although stochasticity generally allows such populations to survive (see Figure 1), this particular populationdoes not survive the first century. The ageing pioneer pionneer population maintains a roughly balanced gender ratio for thefirst fifty years, the number of newborns is small. As the initial settlers become older, they are unable to fully contribute tothe workforce, which dips to 20% after half a century. The latter means that each working adult has to care for five otherdependents in addition to their core duties. The rapid fluctuations in all demographic indicators are a direct consequence oflow-number statistics. Small settler colonies should therefore be avoided at all times, unless the population is steadily resuppliedwith new immigrants.

workforce is thus 58%. Each worker has to care for an

average of 0.76 dependents, and each working couple

typically has 1.52 dependents.

Discouraging childbirth (p0 = 0.5) results in rapid ex-

tinction of the population in the absence of migration,

and encouraging childbirth (p0 = 2) results in a rapidly

growing colony. However, in both cases, the fraction of

the population in the workforce is substantially smaller

than for the natural birth rate (p0 = 1); such colonies

are unlikely to survive, unless robotics can be used to

carry out most work and to take care of the young and

the elderly.

Isolated colonies are thus able to survive for longer pe-

riods of time, provided that (i) the number of pioneers

is large enough to overcome stochastic fluctuations and

interbreeding, and (ii) the colony is able to survive the

population pyramid imbalances during the first 1−2 gen-

erations. The initial batch of inhabitants of the space

colony provide the basic infrastructure for development

of the colony. These pioneers should be carefully se-

lected, as the future success of the colony is in their

hands. Selection choices include, but are not limited to,

(i) the number of pioneers, (ii) the gender ratio, and (iii)

the age distribution. Under the assumption of a reason-

able natural growth rate (e.g., the replacement rate), the

properties of the pioneer population are mostly erased

within several generations. If the population survives,

then, apart from the initial years, the choice for the ini-

tial population is mostly irrelevant.

3.2. Migration-only scenario

In the previous section we discussed the scenario in

which the home planet decides to, or is forced to aban-

don its colony, and the inhabitants of the colony have to

make a living without the help of the home planet. It

Figure 3. The total population of the space colony with noinitial settlers at t = 100 years, for different migration rates(models B1-i to B20-i). Each datapoint shows the mean andcorresponding standard deviations of an ensemble of 100 sim-ulations. The solid line shows the cumulative immigrationrate.

is more likely that the home planet remains interested

in developing the colony and regularly sends new inhab-

itants to increase the viability of the colony. In this

section we consider the scenario in which the colony is

initially unpopulated, and migrants are sent at a roughly

constant rate for permanent settlement in the colony.

We adopt a constant migration rate ∆M = am. Under

standard assumptions of fertility (with a natural growth

rate close to zero), the population is expected to grow

linearly with time: N(t) ≈ amt. Figure 3 shows the evo-

lution of the population for different choices of am. The

total population is systematically below the cumulative

immigration rate. This balance is a result of migrants

reproducing at almost the same rate as their death rate.

The curve is slightly lower due as migrants arrive in the

middle (rather than at the start) of their reproductive

6 Kouwenhoven, Lucero-Prisno, Lin, He & Hao

age, and because migrants are not always able to find a

suitable partner.

3.3. Hybrid scenario

When ignoring stochastical fluctuations, the annual

natural growth rate is roughly

∆B −∆D ≈ 2.17(p0 − 1)N

2 af(5)

Here, the factor two accounts for the presence of equal

numbers of males and females. When including migra-

tion, the total growth rate per capita is then

∆N

N≈ 2.17(p0 − 1)

2 af+amN

+ bm (6)

For large populations (N � 1), the middle term van-

ishes, and after several generations the fraction of mi-

grants among the inhabitants of the colony reaches an

equilibrium in which the fraction of migrants in the pop-

ulation is

R .1

2.17p0(2 af bm)−1 + 1, (7)

where the approximation is more accurate when arriv-

ing immigrants have younger ages, when the population

is larger, and when the elapsed time is larger. The ma-

jority of the colony is immigrant (instead of local-born)

when

bm & 2.17p0(2 af )−1 ≈ 0.013 p0 . (8)

In other words, if the number of migrants arriving at a

large colony (without enforced family planning) is more

than 1.3% of the colony’s population at that time, the

majority of the population will be immigrant. When this

is less than 1.3% of the population, then the majorityof the colony’s inhabitants will be locally born and bred

(in the absence of force family planning).

3.4. Migrant gender policies

Let g = Nm/N be the fraction of males among the

colony’s inhabitants. When the number of males and

females in the colony is not equal, then the fraction of

singles among members of the majority gender is

fsingle ≥ 2− g−1 (9)

where the inequality applies in the case of odd mem-

bership and in the case when a limit in age difference

is applied to partnering. For example, when g = 60%

of the population is male, then at least one third of the

males is single. Such high numbers may cause social

friction that can disrupt the functioning of the colony.

We assume that equal numbers of males and females

are born at the colony. Although females live slightly

longer than males, we assume for simplicity in our mod-

els that the death rates are equal. During the initial

phase of the colony, the gender ratio is determined by

the pioneers, and at larger times, the gender ratio is de-

termined by the properties of the migrant population.

Let gm be the fraction of males among the incoming mi-

grants. For large N and over longer periods of time, the

gender ratio of the equilibrium population can then be

obtained using Eq. (7):

geq =1

2+

(gm −

1

2

)R (10)

and the fraction of singles among the majority gender

is then obtained from Eq. (9). For example, the case

where half of the population is immigrant, immigrant

gender ratios of 55%, 60%, and 70% result in at least

9.5%, 18%, and 26% of the males without a partner,

respectively.

An unbalanced population of migrant genders in-

creases the risk of civil unrest due to high ratios of un-

partnered inhabitants. On the other hand, it contributes

to a reduction of the number of children and therefore

a larger fraction of the population that is available for

the workforce.

Figure 4 shows results for simulations with different

migrant gender ratios for scenarios C1 − 13. The total

population at t = 100 years is not very sensitive to the

migrant ratio. This is because the population growth is

mostly dominated by migration. The final population

tends to be larger for models with equal-gender migra-

tion, but the scatter is large. Male-dominated migration

results in a smaller population than female-dominated

migration, due to the asymmetry in the ability to re-

procude. The average gender ratio of the population

after one century is closer to equality than the gender

imbalance among migrants, due to the contribution of

births in the colony.

We additionally show the maximum rate of singles

(i.e., inhabitants without a life partner) among male and

female inhabitants, for scenarios C1−13. This maximum

rate depends strongly on the migrant gender ratio, and

is roughly symmetric in gender. Note that we chose to

take these maxima as benchmarks, and not the average

rate of single inhabitants. Such maxima regularly occur

due to stochasticity in small populations, due to gen-

der imbalances and large age differences. Even though

a colony may have small single ratios over most of its

lifetime, a high fraction of singles among either of the

genders for a decade can have disastrous effects on the

social stability in the colony.

Population planning for space colonies 7

Figure 4. The effect of the gender ratio among migrants on the space colony population. Left: the total population sizeafter 100 years. The solid line represents the cumulative number of immigrants plus the pioneers. Middle: the gender ratiodistribution on the colony after 100 years. The solid line represents an equal gender ratio. The dotted line represents the genderratio among newly-arrived immigrants Right: the maximum of the ratio of single adult males (solid circles) and females (opencircle) during the period 10 − 100 years.

4. SOCIETY AND HEALTH

4.1. Medical challenges in space colonies

Inhabitants of space colonies will suffer from similar

medical complications as humans on Earth, in addition

to those specific for the environment specific to the space

colony. Infectious and non-communicable illnesses in-

clude, for instance, can range from the common cold,

fever, diabetes, broken legs and allergies, to more severe

complications such as severe wounds, heart attacks, can-

cer and strokes. The overall incidence of such illnesses

is likely to be higher in a space environment due to a

decreased immune system, higher levels of stress, and a

more dangerous living environment.

Space-related health risks are specifically triggered, di-

agnosed, or caused in a space environment or a space-

related environment (such as a Mars colony), with a

larger incidence than on planet Earth. A typical ex-

ample is the higher rate of cancer among space-settlers

due to the absence of the Earth’s magnetic field in space

habitats. Health hazards are specifically associated to

living in space are often related to the lack of oxygen

and water, irregular (or different) circadian schedules,

extreme temperatures, damaging radiation, and long-

term absence of terrestrial gravity.

The first arrivals will likely be exposed to the highest

health risks, due to the initial unavailability of safety

structures and specialised medical personnel, and also

due to the high rate of unforeseen problems and ac-

cidents. A strictly enforced health and safety policy

should maximise a healthy and liveable environment

with minimal risk for hazards. Such a policy should

include a wide range of public health guidelines, such as

those for food safety, medical training, fire safety, hy-

giene, and emergency protocols.

A particular challenge to the healthcare system in a

space colony involves the care of infants, children, preg-

nant inhabitants, patients with mental disorders, and

the elderly. These populations require additional care

from other individuals, and each has their specific ar-

ray of health risks. Notably, the long-term exposure

to space-related health risks on pregnant inhabitants,

newborns, and children are currently still poorly under-

stood.

4.2. Medical treatment

Advanced medical support is an essential part of a

space colony of any size, and prevents inhabitants from

suffering unnecessarily from a medical complication,

such as an injury or a disease. The basic resources re-

quired for a mid-sized colony with several hundreds of

inhabitants include (i) specialists, such as doctors, mid-

wives, dentists, and emergency response personnel, (ii)

caretakers and nurses, (iii) all necessary and potentially

necessary medicine, (iv) medical equipment and machin-

ery, and (v) medical consumables, such as band-aids,

needles, and pacemakers.

A mission or space colony of any population size

should have at least one doctor, and preferably more

than one. Medical doctors with a general training are

initially sufficient, for treatment of injuries, supply of

medicine, and minor surgery. This doctor can be as-

sisted by other inhabitants with basic training, with the

help of robotic surgery, or through telemedicine from

Earth (e.g., Martin et al. 2012). The latter is a viable

alternative when the doctor is unable to attend (e.g.,

due to illness), despite the long interplanetary time lag

for communication. As the space colony grows, higher

demand will develop for additional specialised medical

staff, such as emergency response personnel, psychia-

trists, dentists, surgeons, etc. Only when the space

colony reaches a population size of tens of thousands

to hundreds of thousands, it will become viable to send

highly-specialised medical staff, such as oncologists and

8 Kouwenhoven, Lucero-Prisno, Lin, He & Hao

neurologists. Specialised nursing staff is also not nec-

essary during the initial stage of the space colony’s de-

velopment, as other inhabitants with basic training can

take up such duties in addition to their regular work.

As the population grows above a hundred inhabitants,

full-time nursing/caretaker staff is necessary.

Medicine has to be shipped over from Earth, as a space

colony is unlikely to produce any kind of medicine un-

til it reaches the similar levels of development as Earth.

This includes medicine of all kinds, such as those for

acute treatments (such as paracetamol and antibiotics),

for chronic diseases (such as insulin and thyroxine),

and for public health (such as vaccines). The World

Health Organization’s Essential Medicine list (WHO

2017), used on remote expeditions and for seafaring, pro-

vides a list of basic medicine that should be available to

the inhabitants at any time. As shipping medicine from

Earth can take up to years for a Mars-based colony, the

colony should have sufficient of all types of medicine

stock.

Medical consumables of any kinds, such as band-aids,

blood bags, needles, surgical equipment, and prosthet-

ics, should be shipped in regularly. With the advance of

3D printing technology in the recent decade, it may well

be possible to print the required medical supplies in a

space colony. With the help of the much larger medical

community on Earth, digital designs can be uploaded

to the colony at the speed of light. This approach does

not only allow the colony to have more or less unlimited

access to medical supplies, but is also considerably saves

stockpile and transport resources. Larger medical equip-

ment, such as blood chemistry analysers and ultrasound

scanners, may have to be shipped in when the popula-

tion is over a hundred, x-ray scanning equipment when

the population is over a thousand, while MRI scanners

may require a population size over a hundred thousand.

Finally, as in all societies, death is unavoidable. Strict

protocols are necessary to identify whether or not an in-

habitant has actually deceased, to identify whether or

not a workplace hazard or criminal act has taken place,

and to properly dispose of the remains. The World

Health Organization’s guidelines for death on interna-

tional ships (Schlaich et al. 2009) provides protocols for

similarly remote and isolate situations, which can be

modified for use in space colonies.

4.3. Psychological challenges in space colonies

Despite the medical challenges of living in a space

colony, it is likely that most can be overcome through

intervention with current technology, or technology that

will be developed in the near future. The psychological

condition of the colony’s inhabitants are likely to provide

a substantially greater challenge.

Present-day situations that involve comparatively

long-term missions in which crew members work in

confined spaces in (near-)isolation, include flights to

the International Space Station, military submarine

operations, and research missions to Antarctica (e.g.,

Palinkas 2003, 2004). The participants in such missions

are highly trained and selected to have an excellent

health, and excellent psychological state. These are

often males in their twenties with a strict compliance

to authorities. Inhabitants of colonies, and particu-

larly those on Mars, will have similar challenges, with

three key differences. First, the mission duration is

substantially longer; instead of months on Earth-based

missions, these missions will likely be for life. Second,

as the colony needs a diverse population for survival in

terms of age and gender (see Section 3), there are sub-

stantial restrictions on the selection of migrants that will

be sent to the colony. Third, the second-generation of

inhabitants that are born and bred in the colony itself,

have the properties of the overall human population on

Earth. For a sustainable, long-lived space colony, that

latter is the strongest constraint.

Long-term social isolation and spatial confinement can

result in the development of psychological problems.

This can range from being ”homesick” in the mildest

scenario, to insanity in the worst-case scenario. In the

case of a Mars colony, the travel time of six to eight

months in a confined space, either in isolation or in near-

isolation, poses the first threat.

Psychological stress results in a reduced work per-

formance and reduced social interactions. It increases

the risk of (unintended) work-related mistakes that may

lead to life-threatening situations for the person involved

and/or the other colony inhabitants. In severe situa-

tions, suicidal or nihilistic thoughts may pose a risk to

the colony’s survival chances. Moreover, a psychologi-

cal state of stress is known to have a detrimental effect

human health, and is associated with exhaustion, insom-

nia, immune deficiencies, cardiovascular disease, and an

increased risk for substance abuse (e.g., Rhodes et al.

1990; McEwen 2008).

It is known that a healthy family life can benefit the

psychological state of a person. Although this may not

be true for all human beings, it is for most. The ability

to have a partner and children is therefore a basic ne-

cessity for the long-term survival of a space colony. It

is therefore necessary to constrain the gender distribu-

tion amongst migrants in such a way that the number

of involuntary singles (people who are not in a relation-

ship) is as close to zero as possible. Support from peers,

Population planning for space colonies 9

such as co-workers and friends, can also be highly bene-

ficial in dealing with psychological stress. Finally, online

communication with relatives on Earth is beneficial to

migrants, although it is unlikely to be helpful for those

who were born in the space colony.

Finally, the incidence of clinical mental health issues,

such as depression, dementia, and schizophrenia, will

in the long-term likely be identical to the incidence on

Earth, particularly a few generations after the first ar-

rivals. These patients can be treated clinically, but at

the same time require care from other colony inhabi-

tants.

In the short term, extraction of inhabitants with psy-

chological problems could be viable. This optimises

the functioning of the colony, but it is very resource-

intensive for the colony. In many cases, however, this

may in fact be detrimental to the mental and physical

health of the patient, as the confined space and long-

duration flight back to Earth can substantially worsen

the patient’s situation, unless substantial medical and

psychological care is provided during the duration of the

trip (e.g., Abad et al. 2010), which places a heavy bur-

den on the remaining colony members.

It is therefore imperative to carry out research on hu-

man psychology in space colonies, long before the colony

is established. It is of great importance for the survival

of the colony that all efforts are made to prevent psycho-

logical and mental issues, and that if they occur, they

can be appropriately dealt with in the space colony it-

self.

4.4. Sociological challenges in space colonies

In addition to physical risks, medical issues, and psy-

chological issues, the mutual interaction between the

space colony’s inhabitants may also cause risks to the

functioning and survival of the space colony. A sustained

quarrel between crew members can be devastating to the

morale of a population that lives long-term in a confined

environment. Discrimination of any kind, inappropri-

ate sexual behaviour, excessive macho behaviour (e.g.,

McKay & Lucero Prisno 2012) and bullying, followed by

inadequate reprimanding, may lead to the formation of

factions, with additional risks of violence and/or physi-

cal or psychological abuse. In order to avoid such situ-

ations, strong and disciplined leadership is necessary to

maintain a high level of order and morality for the sur-

vival of the space colony, at least during its initial stage.

A similar approach is taken on submarines on Earth.

Creating strong local leadership has intrinsic risks as

well, and therefore frequent communication with planet

Earth is essential (see Szocik et al. 2016, and references

therein, for a more detailed analysis). Appropriate en-

tertainment and relaxation facilities may contribute to

a socially healthier environment as well.

Another issue that, when ignored, may have devas-

tating consequences for the space colony’s future is the

nursing, nurturing, and education of children and young

adults (see also Szocik et al. 2018). Under the stressful

conditions of living in a space colony, it is essential that

children are raised with discipline, in an environment

with peers, and ideally (but not necessarily) in a core

family.

In order to maintain a healthy population balance,

with a sufficiently large fraction of the population of the

population available for the workforce, it is essential that

small (N . 100) populations have strict and enforced

family planning regulations. This may not be a popular

measure, but as seen in the previous sections, it is a

great contributor to the survival probability of the space

colony, unless the migration rate is substantial.

4.5. Labour division and training

A disciplined division of labour is necessary for the

survival of any small and remote population on Earth,

and this is even more important for a future space

colony. A small group of initial pioneers should be

able to maintain a safe, productive, and socially healthy

environment. Although the list of occupations in the

present-day society is well-known, it is unlikely that the

division of labour in a space colony is remotely simi-

lar to that on Earth. Small colonies (with populations

of less than a hundred) clearly need a doctor, but they

are unlikely to require any of the most common jobs

on Earth (such as cashiers, waiters, accountants, truck

drivers, and web developers). To ensure basic opera-

tions of such a space colony, the following labour types

are required at minimum:

• Medical personnel, psychologists, and caretakers

• Governance and law enforcement personnel

• Robotic engineers; information and communica-

tion technologists

• Electronic engineers and computer scientists

• Pilots, transport and navigation specialists

• Mission specialists, for space colonies with a spe-

cific economic or scientific purpose, such as biolo-

gists, astrophysicists, environmentalists, or miner-

alogists

• Technical staff responsible for general mainte-

nance, food supply, and mission-related labour.

• Educators and trainers

10 Kouwenhoven, Lucero-Prisno, Lin, He & Hao

This in-exhaustive list may need to be expanded or

reduced based on the size of the space colony. Large

colonies may have specialised law-enforcement officers

and school teachers, while small colonies may require

individuals to take up multiple roles. For example, one

person may take up all tasks related to medical duties,

such as emergency response, consultation, providing and

safeguarding medication, nursing and care-taking du-

ties, and psychological care. The burden of care for the

young, the elderly, and the sick should not be underes-

timated. The initial population is likely to consist of a

young, healthy crew, but health issues and ageing will

become costly only several decades later. This requires

a balanced and well-planned age distribution planning

(and family planning) among the first settlers and the

migrants that follow.

It is important to continuously have backup-staff

available, for example in the situation when the space

colony’s doctor is critically injured, or when the se-

curity officer suffers from psychological trauma. In

small colonies with fewer than 50− 100 inhabitants, the

best practice to ensure a continuous supply of a cer-

tain labour expertise is continuous education of trainees

whose main task is somewhat related to the required

expertise. It should be noted that in the modern world,

such training can also be carried out remotely or with

the aid of virtual online environments. Migrants from

planet Earth should also be carefully selected based on

their educational background and technical skills, in

addition to the demographic requirements, in order to

compensate for imbalances in the space colony’s work-

force. For large space settlements in orbit around the

Earth, this expertise will be delivered in days, but on

a remote Mars colony, it may take years for these mi-

grants to arrive. The availability of back-up personnel

is thus essential in the latter case.

Due to the advances in computing power and artifi-

cial intelligence, it is likely that many of the tasks in a

space colony will be executed using advanced computer

software and/or robotic devices (e.g., Hamming 2018).

In the modern-day world, this is revolution in labour is

already ongoing at many levels in society, from robotic

vacuum cleaners to artificial intelligence-assisted diag-

noses of chest x-ray screenings (e.g., Guevarra 2018).

The constraints on the labour requirements in space

colonies will likely speed up these developments, which

may render many of the common jobs in our present-day

society as redundant.

The shortage in labour expertise also makes it in-

evitable to make optimal use of the space colony’s labour

resources. This means a full equality among genders,

and abandoning traditional gender roles. In addition,

the concept of retirement may have to be abandoned

completely, as the elderly may still be fully capable of

carrying out their assigned duties, such as educators,

scientists, or inhabitants with leadership positions.

5. CONCLUSIONS AND NEXT STEPS

We investigate the evolution of a human population

in space colonies, and how demographic policy decisions

can affect the stability and survival of a space colony.

We carry out simulations that include migration, birth,

partnering, and death, and determine a set of criteria

that can be used to determine whether a colony is able

to survive. Finally, we address the issues of medical

and psychological care, and the social impact and labour

division risks in space colonies.

We find that the demographic properties of the ini-

tial settlers of the space colony, and the selection of the

migrants, are among the key determinants for the sur-

vival of the space colony. For small populations the key

contributor to colony demise is population stochastic-

ity, while for larger populations, which have substan-

tially higher survival rates, the most important risk is

demographic imbalance. Space colonies that are formed

through a one-time settlement (i.e., no subsequent mi-

gration) can survive for long times, provided that the

initial population is large enough (N & 100), and that

the colony is able to survive the baby booms and age-

ing booms during the first century. In such a scenario,

increasing or decreasing the birthrate over beyond the

replacement rate is ineffective for small populations, and

results in unbalanced populations and an inability of the

space colony to survive. Steady migration from Earth

to the colony can mitigate these problems. The frac-

tion of the population that is available for the workforce

can be adjusted through the migration rate, the gender

distribution among migrants, and the family planning

policy, and all should thus be carefully planned. So-

cietal factors such as the labour force distribution, the

impacts of technology, communication, culture, politics,

and healthcare are difficult to predict, as there are no

comparable precedents in human history. Scientific re-

search (technological, medical, and psychological), com-

bined with new technologies (communication, robotics,

artificial intelligence, and 3D printing), will likely pro-

vide us the knowledge necessary to develop and accu-

rate framework for a planned space settlement within

a decade, provided that the present-day society has the

willpower.

The future possibility of establishing a space colony is

challenging. The greatest challenge is probably not tech-

nological or medical. The greatest challenge is likely to

be the construction of an functional and efficient society

Population planning for space colonies 11

in which satisfies the social requirements that we make

as a human society. During the planning phase and the

initial establishment of a space colony, we will likely be

confronted with decisions that will challenge the norms

and values that we have in our societies around the world

(see also Kramer 2011; Smith 2016). Controversial is-

sues will debated, such as abortion, euthanasia, liberal

family planning, gender roles, the freedom to choose

ones own profession and/or partner, and difficult choices

have to be made in order to balance the demands for

economic progress, social stability, security, and safety

with human dignity and personal choice. The society

on planet Earth is diverse, and it is not known how the

new society in the space colony will culturally evolve.

Perhaps it will be dominated by the culture of the na-

tion(s) that provide most effort to establish the space

colony. Perhaps it will be a homogeneous or heteroge-

neous mixture of the different societies on Earth. Or

perhaps, in the long term, a remote space colony will

gradually evolves towards developing its own culture and

society values that may be considerably different from

those on Earth.

Acknowledgments. This project received seed funding

from the Dubai Future Foundation through Guaana.com

open research platform (Mohammed bin Rashid Space

Settlement Challenge - grant number MBR007).

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