Cave habitation on Mars could enable an initial human settlement by providing natural protection from radiation and hazards in the Martian environment. The document discusses assessing cave habitation by analyzing the feasibility, engineering challenges, social impacts, and international cooperation required. It suggests lava tubes could serve as shelters, with stable temperatures and low radiation levels inside. Remote sensing would first need to detect caves to identify potential sites, before robotic and human missions could explore the caves in more detail.

1. 0
... to develop a mission architecture for an initial settlement
on Mars by assessing the feasibility of cave habitation as an
alternative to proposed surface-based solutions.
Mission Statement
Introduction
Human Cave Program
Alternative Program
Mars Caves
Governing Frameworks
Future Considerations
1
2
3
4
5
6

2. ACCESS Mars will assess habitation scenarios that maintain
crew health and safety in the Martian environment, while
allowing them to perform key science and exploration tasks.
Aside from the engineering and technological challenges of
such a mission, the assessment of cave-based solutions will
also address issues related to social impact, international
cooperation, policy, law, and planetary protection.
Scope
Overview
Introduction
A human mission to Mars will be a bold endeavor and will
launch humankind into a new era of space exploration.
Given the complex technical and ethical dimensions in-
volved in exploring another planet, it will be necessary to
manage and optimize the associated benefits while reducing
the risks and hazards to crewmembers on Mars.
This requires consideration and analysis of diverse subsur-
face habitation options such as lava tubes. The advantages
of lava tubes include, but are not limited to, shielding against
radiation, protection from surface environmental hazards,
the possible discovery of unexplored scientific opportuni-
ties.
“Two thousand years from now,
their descendants might walk
into this chamber … the first hu-
man dwelling built on Mars! ...
They were like Cro-Magnons in a
cave,livingalifethatwascertain
to be pored over by the archae-
ologists of subsequent genera-
tions… ”
Kim Stanley Robinson, Red Mars
The Lava Caves National Monument, California, yielding unexpected plant
growth.
Image: National Park Service

3. 1
Never before in the history of humankind have people
left their home planet to settle permanently on another
celestial body. Present generations must extend the work
accomplished during the Apollo era and commit to a new
vision of exploration to include an initial settlement on
Mars.
Caves have been and still are natural protection against
hostile environments. They also represent the cradle of
human culture and society and are still in use today. It is
therefore likely that caves on Mars may provide the protec-
tion and security necessary for crew members to establish an
initial settlement.
The first humans on Mars can use the knowledge of
terrestrial cave dwellings to adapt more easily to a hostile
environment, paving the way for a permanent human settle-
ment on the planet. ACCESS Mars focuses on caves because
of their known presence and potential benefits, including
hazard protection against the extreme Martian environ-
ment, and engineering advantages. A precursor mission to
the Moon can help investigate future Mars mission aspects
such as crew size, mission duration, exploration strategies,
level of complexity and capability of tools, the application
of light-weight and inflatable structures, the reliance on
robots, and the dependence on local resources.
Rationale
Natural and man-made caves have traditionally served as human dwellings,
housing both simple wine cellars and complex temples.
Image: John C. Pint
Exploring the Harrat Lavatube: An analog for future EVAs.
Image: John C. Pint
“There is a free resource that exists
on the Martian surface – caves.”
Penny Boston

4. Mars Caves
Why cave habitation?
Lava tubes have recently been found on Mars. Due to their
known presence in volcanic areas and their size, shape,
and sound structural stability, their use as human habi-
tats is promising. The potentially smooth flat floor and
accessible entrances near the surface reinforce this concept.
The low radiation levels, protection from dust storms and
stable temperatures within these caves provide a safe natural
environment for both humans and robots. The notion of a
long-term settlement on Mars is supported by the presence
of natural hazard protection.
How do we detect caves?
The detection of cave entrances and determining the key
cave parameters through remote sensing is required before
robotic and human missions can take place. A promising
technological option for this task is thermal sensing from
a satellite platform. By measuring the thermal variations
of the cave entrance in comparison with the surface, caves
can be differentiated from mere holes in the ground and
key properties of the cave such as length and diameter can
be deduced. However, to find caves, we must know what
to look for. Measurements of analog sites on both Earth
and the Moon will provide the necessary knowledge to more
accurately identify caves on Mars. Once caves have been
identified through remote sensing detection, surface robotic
precursor missions will be required to investigate the caves
of interest to assess cave usability and available resources, as
well as astrobiological signatures. This will ultimately permit
the appropriate selection of a cave as a human habitat.
Various volcanic regions on Mars have evidence of lava tubes and available
resources for use. Accessing these regions will open the possibility of rich science
and allow long term settlement. Image: NASA (Background terrain)
The smooth floor surface and uniform shape of lava tubes as found on Earth
provides ideal spaces for an artificial habitat structure and mobility.
Image: Line Drube

5. 2
What makes a good landing site?
Selecting the proper cave requires careful planning. It must
meet physical requirements for habitat design, and be suit-
ably located such that both survival and mission return can
be assured. Nearby water ice, mineral sources and the scien-
tific value of the local environment also determine wheth-
er the site is appropriate. Although shallow ground ice is
known in polar regions, it is anticipated that ice is globally
present deep under the subsurface. Access to this resource
is not only essential for human survival, but might be facili-
tated through the use of caves. The scientific interest of a
particular site is also a main driver. The presence of meth-
ane, remnant magnetism and the evidence of life could dra-
matically change our understanding of Mars.
What resources exist there?
Water ice on Mars is central for human exploration. It will
allow autonomy from Earth and thus facilitate long term
settlement. The significant weight reduction in required
stored consumables may in fact render the mission techni-
cally feasible. Both the ambient air and the Martian regolith
may be converted to oxygen, an essential ingredient for the
life support system and fuel. For secondary power genera-
tion, both solar and geothermal sources may be used. Iden-
tifying new resources and learning their retrieval and uses
will lead to sustainability and self sufficiency. Although the
restriction to lava tubes for site selection could be limiting
compared to a surface habitat, they offer an entry to cur-
rently unknown subsurface resources such as ice, energy
sources and minerals.
This shows an observed partially collapsed lava tube on Mars with a diameter
of several hundred meters. Un-collapsed portions could be ideal for habitation
Image: NASA

6. Human Cave Program
Will caves affect mission planning?
Using Martian caves will pose challenges regarding human
mission planning, in that it implies some changes in the car-
go launching campaign defined in the latest NASA Design
Reference Mission. Operating a cave habitat will require ex-
tra cargo shipments in addition to subsurface communica-
tion capabilities and underground robotic support.
How would they serve as habitats?
Caves on Earth provided shelter in the early stages of human
history. This time around Martian caves can play a decisive
role in providing humans with shelter and logistic support
for human exploration of Mars, replacing heavy structures
and shielding required for a surface habitat.
Human habitats will still have to be constructed and de-
ployed inside caves. However, requirements will be much
less strict, as many caves provide extensive protection from
meteorites, radiation, and dust storms. This provides prime
conditions for inflatable structures technologies to be used
for habitats inside caves. Mass reduction allows us to take
full advantage of our launch capacities and enables faster
expansion of a modular habitation infrastructure. Tempera-
ture fluctuations in caves are less severe and therefore put
less strain onto thermal and power systems.
Dynamic lighting systems can be employed to simulate day-
light, which is fundamental to human wellbeing in an envi-
ronment with low natural light, as well as for horticultural
applications.
Illustration of an Inside Cave Habitat (ICH) with two inflatable modules.
Image: ACCESS Mars
“We are children of Earth,”
Hiroko said, loud enough for all
to hear. “And yet here we stand,
in a lava tunnel on the planet
Mars. We should not forget how
strange a fate that is. Life any-
where is an enigma and a pre-
cious miracle…”
Kim Stanley Robinson, Green Mars

7. 3
Can caves help Mars Exploration?
Caves are both prime candidates for supporting human ex-
ploration of Mars and also test beds for scientific explo-
ration. Given the strong astrobiological potential of caves,
sub-surface environments, and the characteristic environ-
mental conditions inside caves, are typically different from
surface conditions.
Crews will be expected to act highly autonomously, as no
real-time support possibility exists between Earth and Mars.
Consequently, crews must become medically autonomous.
The crew should be trained as field scientists in Mars cave
analog environments to guarantee a good performance for
the necessary Mars cave-specific operations.
Reducing overall radiation, which will allow the mission
crew to extend EVA time and perform more scientific ex-
ploration of the planet surface as well as the cave interior.
Temperature conditions inside and at the entrance of caves
may also allow implementation of new closed loop life sup-
port system, and an increase in the performance of existing
technologies.
Some technical capabilities and scientific information that
would be required to allow humans to live in caves on Mars
are missing. Therefore, precursor missions will be needed, in
order to test planetary technology and in-situ resource utili-
zation (ISRU) or sending robots to explore potential caves.
A multi-functional Mars base could include a greenhouse.
Image: NASA
Future exobiology and geology research on Mars — on the surface, and below.
Image: NASA

8. Access Mars
A Vision of Exploration
Permanent Presence
Robotic Reconnaissance
Human Exploration
The Search for Life
Cave Habitats

10. Capacity USA Russia
MANNED
Access To LEO Yes Yes
Earth Re-Entry Yes Yes
Life Support System Yes Yes
LEO Rendez Vous Yes Yes
Transfer to Moon/Mars Orbit Yes No
Mars EDL Anticipated No
Moon Landing Yes No
Surface Habitat Anticipated No
Rover/Mobility Capability Yes No
Moon Surface to LLO Yes No
Mars Surface to LMO No No
UNMANNED
Access To LEO Yes Yes
Transfer to Moon/Mars Orbit Yes Yes
Earth Re-entry Yes Yes
Moon Landing Yes Yes
Mars EDL Yes Yes
Rover/Mobility Capability Yes Yes
Autonomous Rendez-vous Anticipated Anticipate
Moon Surface to LLO Yes Yes
Mars Surface to LMO No No
Yearly Foreseable Budget
($ Billions)
18 1.5
Governing Frameworks
What role does law play?
A human mission to Mars raises certain legal issues for com-
pliance under both international and national law. In fact,
the four main space law treaties delineate the rights and ob-
ligations of states in conducting space activities. The current
legal regime applies equally to both surface-based or cave-
based habitat solutions.
Important legal concepts include:
■■ No national appropriation of Martian territory is al-
lowed; no private or public entity can claim a piece of
Mars territory.
■■ States have an equal right under the Outer Space Trea-
ty to explore, exploit, and use Martian resources. This
includes mining on Mars, water extraction, and other
ISRU activities.
■■ States must authorize and supervise national and private
entities involved in space activities. This includes enact-
ing law and licensing regimes to ensure compliance with
the treaties.
■■ States are internationally responsible and could be liable
for damage caused as a result of their national space
activities.
■■ In pursuing activities on Mars surface and subsurface,
States must take appropriate measures to avoid harm-
fully contaminating the Martian environment. Likewise,
precautions should be taken to avoid adversely affecting
the Earth as a result of Martian exploration.
Overview of international State space capabilities as of 2009
Stakeholder matrix illustrating areas of focus for gaining
global public, private and governmental support

11. China Europe Japan India
Yes No No No
Yes Anticipated Anticipated No
Yes Anticipated No No
No No No No
Anticipated No No No
No No No No
No No No No
No No No No
No No No No
No No No No
No No No No
Yes Yes Yes Yes
Yes Yes Yes Yes
Yes Anticipated Anticipated No
Anticipated Anticipated Anticipated No
No Anticipated Anticipated No
No Anticipated No No
ed No Yes No No
No No No No
No No No No
n/a 7 2 1
4
Policy Considerations
A human Mars mission involves several major policy con-
siderations. They include the capacity for international co-
operation and contribution, an analysis of the significance
or benefits of a Moon/Mars exploration strategy, and as an
analysis of the benefits of precursor missions.
As international cooperation is essential for such a mission,
consideration should be taken for each country’s specific
technical capabilities and yearly budget.
Looking at precursor missions, it appears that there is a solid
case for a combined exploration strategy, first using the In-
ternational Space Station (ISS), then landing on the Moon,
and eventually setting foot on Mars. Indeed, such a program
would allow gaining the necessary confidence in the required
technologies in a progressive, and affordable, manner.
Society
The main stakeholders that should be targeted on are gov-
ernments, space agencies, large aerospace companies, and
the public (taxpayers, mass media & social media) espe-
cially in the area of interest of social impact, technology,
engineering, and economical prosperity. These results show
these areas of society that have the most influential impact
on the Mars mission; thus, time and effort need to be dedi-
cated to these stakeholders to maximize the ability for a suc-
cessful mission.

12. Alternative Program
As a result of our investigation, an alternative scenario
for a permanent human presence is proposed in addition
to the ACCESS Mars Design Reference Mission. Six crew
members stay for two rotations (~1300 days), creating an
overlap of twelve people in the habitat for eighteen months.
­­Doubling the number of crewmembers and time spent
on the Mars surface introduces both benefits and risks. A
permanent presence on Mars will provide valuable contri-
butions to science and technological innovation. At the
same time, the increase in mission duration and crew size
will affect the mission parameters. Consequently, recom-
mendations and suggestions are provided to mitigate the
associated risks.
Impact of Mission Duration
Overview
Extending the presence of a crew on the surface from 18 to
48 months will lead to a reduction in mission hardware life
time due to wear and tear. Therefore, the designs should be
adapted to ensure continuous operability of the settlement.
Using caves as an equipment shelter may decrease the harm-
ful impacts of the Martian environment.
Likewise, radiation can be reduced by using caves as protec-
tive shields for the habitats. In fact, a surface habitat for long
duration missions may not otherwise be possible due to the
extreme radiation on Mars.
While longer missions may increase the risk of health is-
sues such as acute respiratory infections, urinary calculus,
and psychological implications, countermeasures are being
developed in technology, in training, and in selection pro-
cedures to reduce risks. For instance, technology exists for
designing dust repelling suits and surfaces, as well as dust
filtration systems.
ACCESS Mars Extended DRM
Image: ACCESS Mars
T-14 months,
1st Cargo,
Cave Habitat
and Surface
Habitat Mars
Transfer Ve-
hicle (MTV)
arrive. Cargo
and Cave
Habitat MTV
Land on Mars.
Surface Habi-
tat MTV stays
in orbit.
T+6 months,
Crew 1 MTV
arrives. Crew
transfers to
Surface Habi-
tat MTV and
land on Mars.
Crew 1 MTV
stays in orbit.
T+10 months,
2nd Cargo,
Cave Habitat
and Descend-
ing MTV ar-
rive. Cargo
and Cave
Habitat MTV
Land on Mars.
Descending
MTV stays in
orbit.
1 2 3

13. 5
Impact of Crew Size
Increased crew size allows more specialization amongst the
crew in medicine, engineering, and science, thereby enhanc-
ing their ability to solve problems that may arise; however,
personal and cultural diversity among the crew introduces
social interaction difficulties.
Other considerations for mission planning include changes
in workload, safety, habitat occupancy, and level of privacy,
based on occupancy level. For example, while the habitat
is fully occupied, the crew will have increased personnel
redundancy (in case of sickness or injury), but decreased
equipment redundancy.
An enlarged crew increases international participation, as in
the ISS model.
Further research/studies are required to identify other im-
plications of increased crew size. For example, planetary
protection issues cannot be properly assessed until the im-
pact of a single crewmember on an extraterrestrial environ-
ment is quantified.
Impact of Human Presence
Establishing a permanent human presence on Mars will al-
low continuous operations and maintenance of the explora-
tion infrastructure.
In addition, operations are simplified by knowledge han-
dovers between crews. Conversely, crew training, including
‘inter-crew’ training, should be modified to enhance inter-
personal relationships.
International community responsibility for continued hu-
man missions on Mars will increase mission success, as was
demonstrated on the International Space Station (ISS) after
the Columbia accident in 2003. The international communi-
ty preferred reducing the crew size over abandoning the ISS.
As prolonged human presence and Mars colonization takes
place, Mars international nationality may be created. This
will affect Earth culture and the necessity for Martian law.
T+32 months,
Crew 2 MTV
arrives. Crew
transfers to
Descending
MTV and land
on Mars. Crew
2 MTV stays in
orbit.
T+36 months,
3rd Cargo and
Descending
MTV arrive.
Cargo MTV
Land on Mars.
Descending
MTV stays in
orbit.
T+50 months,
Crew 1 depar-
ture to Earth
and arrives at
T+56 months.
54 6

14. General Recommendations
Astrobiology & Planetary Protection
ISS and Lunar bases should be used as stepping stones in
establishing a permanent Martian habitat.
A need exists for an in-depth study of Martian caves to fur-
ther our understanding of potential hazards such as small
meteoroid flux, surface radiation, cave stability (materials,
fractures, structure), electrical environment and lighting sys-
tems etc.:
■■ By using Earth and lunar analogues
■■ Through precursor robotic missions and research.
Further consideration of alternate mission scenarios are
needed in order to achieve a long-term sustainable human
presence on Mars.
Extravehicular activities and the exploration of the un-
known in the foreign environment of Mars are a natural
progression of the curiosity of humankind. However, plan-
etary protection policies are inextricably linked to planetary
exploration. ACCESS Mars recommends better and more
cost-effective instrument-sterilization and anti-contamina-
tion procedures to satisfy these policies. Improved technol-
ogies may also help facilitate more astrobiology exploration
missions, which should adhere to the COSPAR Planetary
Protection Policy. Further debate pertaining to the evolution
of planetary protection policies on a global scale (should a
consensus be reached) will be beneficial given a multilateral
desire to explore beyond Earth. Finally, if planetary explora-
tion rights are thought of as earned privileges, a policy sce-
nario might reward advances in the sterilization of robotic
instrumentation with increasing planetary exploration privi-
leges, perhaps using the moon as a test bed for practicing
protection procedures.
Future Considerations
International Space Station seen from STS-127.
Image: NASA
Now was their chance,
for all of them together in this
present — ghosts could watch,
from before and after, but that
was the moment when what
wisdom they could muster
had to be woven together, to
be passed on to all the future
generations.
Kim Stanley Robinson, Blue Mars

15. 6
Conclusions
As humanity endeavors to become a two-planet civilization,
the use of Martian caves can provide an excellent initial so-
lution to some of the problems posed by the various haz-
ards on the planet. With time, it is possible that new tech-
nologies will lead to more discoveries on how to thrive on
Mars, thereby fully realizing a new era of space exploration.
By continuing to Assess Cave Capabilities and Evaluating
Specific Solutions, we will leave the cradle of Earth, effec-
tively accepting the challenge of exploring the unknown and
pushing the limits of knowledge beyond our home planet.
Future Technologies
Many hazards and surface constraints on Mars are mitigated
by cave habitats, which will be very important until future
technologies are developed. Recommendations include:
■■ The recovery of materials necessary for human life and
habitat construction out of the Martian regolith and at-
mosphere;
■■ Using materials with an atomic number less than alumi-
num for radiation shielding to reduce secondary radia-
tion, e.g. liquid hydrogen;
■■ Improving EVA suit mobility, possibly in the form of
mechanical counter-pressure suits;
■■ Implementing technology to protect humans and equip-
ment from dust storms;
■■ Developing advanced propulsion systems, which may
make Earth-Mars transits faster and less costly;
■■ Advancing ISRU technology for recovering materials
necessary for human life and habitat construction from
the Martian regolith and atmosphere;
■■ Studying futuristic concepts such as nuclear fusion reac-
tors
Possible concept of surface exploration on Mars.
Image: NASA

16. The authors gratefully acknowledge the generous guidance, support and
direction provided by the following individuals during the course of this
work:
Project Faculty
René Laufer
Alfonso Davila
Jhony Zaveleta
Beatriz Gallardo
Design & Content
ACCESS Mars Effort.
The authors are also grateful for the advice and support of all faculty,
teaching associates, staff, advisors and visiting experts of the Interna-
tional Space University.
Authors
A. Al Husseini, L. Álvarez Sánchez, K. Antonakopoulos, J. Apeldoorn,
K. Ashford, Jr., D. Atabay, I. Barrios, Y. Baydaroglu, K. M. Bennell, J.
Chen, X. Chen, D. Cormier, P. Crowley, G. de Carufel, B. Deper, L.
Drube, P. Duffy, P. Edwards, E. Gutiérrez Fernandez, O. Haider, G.
Kumar, C. Henselowsky, D. Hirano, T. Hirmer, B. Hogan, A. Jaime Al-
balat, E. Jens, I. Jivănescu, A. Jojaghaian, M. Kerrigan, Y. Kodachi, S.
Langston, R. MacIntosh, X. Miguélez, N. Panek, C. Pegg, R. Peldszus, X.
Peng, A. Pérez-Poch, A. Perron, J. Qiu, P. Renten, J. Ricardo, T. Sarace-
no, F. Sauceda, A. Shaghaghi Varzeghani, R. Shimmin, R. Solaz, A. Solé,
R. Suresh, T. Mar Vaquero Escribano, M. Vargas Muñoz, P. D. Vaujour,
D. Veilette, Y. Winetraub, O. Zeile
Sponsors
NASA Ames Research Center
NASA Exploration Systems Mission Directorate (ESMD)
Additional copies of the Executive Summary, Final Report and Project
DVD may be ordered directly from the ISU Central Campus:
International Space University
Parc d’Innovation
1, rue Jean-Dominique Cassini
67400 Illkirch-Graffenstaden, France
Email: publications@isu.isunet.edu
Credits & Acknowledgements