Bhartiya Extraterrestrial Expandable Modular Habitat: A Modular Panel Based Architecture

Abstract

A modular panel-based extra-terrestrial habitat - the Bhartiya Extraterrestrial Expandable Modular Habitat (BHEEM) - is proposed here. We employed a constraint that individual elements of the habitat should be stackable in the payload faring of a suitable launch vehicle (Starship). Our design methodology consisted of using the bottoms-up approach to humancentered design. We studied the various activities that are necessitated for lunar and martian missions and calculated the average volume requirement for a single human to optimally complete the activity. The activities are then aggregated to provide segregated volumes that would function as standalone pressurized modules. A panel-based modular architecture is proposed that would join to form the various pressurized modules. We extensively explored the possible configurations that can be formed from simple panel shapes such as triangles, squares and pentagons. A comparative analysis was done on the solids, and the best solids were selected based on their volume efficiency and structural rigidity. The structural rigidity of each module was determined by using numerical analysis and further validated by analytical methods. Based on the volume and activity requirements, we have proposed a layout that can be constructed with BHEEM’s architecture. A single payload of the starship is sufficient to deploy the proposed layout providing twice the volume of the ISS. BHEEM’s modular nature and shape design ensure comfort for astronauts to conduct daily activities while making mission logistics and transportation with payloads of lesser capacities easy. The panel-based architecture allows for easy construction, repair, and maintenance of the habitat.

Full text

Bhartiya Extraterrestrial Expandable Modular Habitat:
A Modular Panel Based Architecture
Mritunjay Baruah1 , Amogh Ravindra Jadhav1 , Bimalendu Mahapatra1 , Shubhanshu
Shukla2 , Aloke Kumar1*
1. Department of Mechanical Engineering, Indian Institute of Science, Bangalore-
560012, India
2. Indian Space Research Organisation, Department of Space, Antariksh Bhavan,
Bangalore-560094, India
*Corresponding author: alokekumar@iisc.ac.in
ABSTRACT
A modular panel-based extra-terrestrial habitat - the Bhartiya Extraterrestrial Expandable
Modular Habitat (BHEEM) - is proposed here. We employed a constraint that individual
elements of the habitat should be stackable in the payload faring of a suitable launch vehicle
(Starship). Our design methodology consisted of using the bottoms-up approach to human-
centered design. We studied the various activities that are necessitated for lunar and
martian missions and calculated the average volume requirement for a single human to
optimally complete the activity. The activities are then aggregated to provide segregated
volumes that would function as standalone pressurized modules. A panel-based modular
architecture is proposed that would join to form the various pressurized modules. We
extensively explored the possible configurations that can be formed from simple panel
shapes such as triangles, squares and pentagons. A comparative analysis was done on the
solids, and the best solids were selected based on their volume efficiency and structural
rigidity. The structural rigidity of each module was determined by using numerical analysis
and further validated by analytical methods. Based on the volume and activity requirements,
we have proposed a layout that can be constructed with BHEEM’s architecture. A single
payload of the starship is sufficient to deploy the proposed layout providing twice the volume
of the ISS. BHEEM’s modular nature and shape design ensure comfort for astronauts to
conduct daily activities while making mission logistics and transportation with payloads of
lesser capacities easy. The panel-based architecture allows for easy construction, repair,
and maintenance of the habitat.

1. Introduction
On April 19 1971, the Salyut-1 was launched as the first space station in low earth orbit that
was designed for a crew of 3. It was the first space habitat deployed in space. The next 10 years
saw the launch of 6 subsequent Salyut space stations, along with the Skylab in 1973 and Mir
in 1986. Salyut-6 was the first ‘second generation’ space station that had two docking ports
allowing for replacement of crew and longer human habitation in space [1]. The Mir marked
the ‘third generation’ of space stations, being the first to have a modular design that was
assembled in orbit. All the space stations before this were monolithic [2]. Till today we only
have two additional space stations that have been launched after Mir that are crewed and still
operational – the International Space Station (ISS) launched in 1998 and the Tiangong Space
Station whose final stage launched in 2021. In recent years there has been renewed interest in
long term habitation and potentially establishing a permanent base on the Moon [3]. This will
facilitate future missions to send humans to Mars. The Artemis program with the Gateway
space station and the International Lunar Research Station are current proposed missions that
are looking to accomplish this task. Sufficient infrastructure on the Moon or Mars will pave
the way for humanity to become a multiplanetary species allowing us to expand to other planets
or celestial bodies.
The two existing space-stations have already established a legacy by contributing to the
knowledge pool of our understanding of science and the creation of innovative spinoffs for
applications on Earth. Scientists have used microgravity—onboard the Russian Space Station
Mir, the Space Shuttle, and the ISS—to improve molecular crystal growth research as
microgravity-grown crystals from space leads to better images of the structures back on Earth
[4]. Combustion experiments in microgravity are also being carried out to reduce pollutant
emission in practical terrestrial combustion [5]. Current research in bio-printing in
microgravity opens the future potential for advanced medical treatment in space [6, 7],
manufacturing food sources during spaceflight [8], or for the creation of bioreactors and life
support systems for long term habitation [9]. These accomplishments are remarkable, but we
are yet to enter the age of having long term permanent space base on extra-terrestrial soil.
Among the several challenges of space exploration, one of the most important is logistics. The
cost of space launches had dropped from very high levels in the first decade of the space age
but then remained high for decades and was especially high for the NASA’s Space Shuttle. In
the most recent decade, commercial rocket development has reduced the typical space launch
cost by a factor of 20 while NASA’s launch cost to ISS has declined by a factor of 4. Owing to
its reusability feature, SpaceX’s Falcon 9 advertises a cost of $62 million to launch 22,800 kg
to LEO, i.e. $2,720/kg [10]. The new Starship, which is the biggest rocket ever built and is
under development proposes an astonishing cost of $10/kg [11]. The launches are also
dependent on the payload fairing volume. The starship, for instance, has a payload capacity of
around 800 cubic m [12]. Habitable payloads are even more complex as they need to be human-
rated and have sufficient habitable volumes for humans to thrive. It is necessary for habitats to
consume the least volume during transport while providing the most volume when inhabited.
Other challenges such as micro-meteorite orbital debris (MMOD) and solar and cosmic
radiation are also important to be considered [13, 14, 15] as they can significantly impact
mission success and human health.

There are a multitude of solutions that have been used in the past to tackle the challenges of
habitation in space. Initially space habitats used to be just small monolithic capsules intended
for sorties (short to and fro mission). Subsequent launches saw the emergence of space stations
with modular design principles. The ISS and the Tiangong Space Stations are classic examples
of this. The need for collapsibility to facilitate volume expansion upon deployment gained
popularity which led to the creation of inflatable habitat designs like TransHab and the Bigelow
Expandable Activity Module (BEAM). The primary advantage of inflatable space structures is
in their ability to be compactly stowed for launch and then subsequently deployed to a much
larger operational volume. This packaging enables the use of smaller launch vehicles or the
ability to package multiple inflatable structures on a larger launch vehicle. These structures
also have the potential for mass savings due to the use of high-specific strength materials, such
as Vectran or Kevlar, and the reduced impact of launch loads on the design due to the initial
packaged state. [16]. There are many new concepts that researchers and organizations are
testing such as the Tesserae from the Massachusetts Institute of Technology (MIT), which is a
self-assembly panel-based orbital habitat or the Moon Village from the European Space
Agency (ESA), which is an extraterrestrial colony of inflatable habitats [17, 18].
One of the first challenges that needs to be addressed for the design of a habitat is the volume
confinement problem. A well-designed habitat will keep in mind the human needs and provide
sufficient volume to carry out tasks in an efficient manner. It becomes critical to account for
the various activities in advance and accurately calculate the volume requirement. The
architectural tectonic of how the volume is to be made is also important since it sets the
direction for the manufacturing and construction of the habitat. Another challenge is the
logistics and transportation of the key habitat elements, especially when weight and volume
are of limiting factor. Ideally, we would want our habitat to occupy the least amount of volume
when being transported while providing the most volume when being used. The solution to
these challenges builds the foundation on which further material research, interior design, and
prototype construction can be done.
In this paper, we present BHEEM – the Bhartiya Extraterrestrial Expandable and Modular
Habitat, a design concept that solves the problem of building a permanent human base on Moon
or Mars. BHEEM’s design keeps human needs first. The unique panel-based architecture has a
modular tectonic that provides many advantages for space applications. A variety of layout
configuration for a variety of missions can be built by the joinery that encodes all the necessary
information. The feasibility of BHEEM’s design has been validated using numerical analysis.
The modular and compact design allows it to be transported on rockets with lesser payload
capacity and provides substantial packing to deployment volume ratio.
2. Methodology
Our design methodology keeps human needs first and is inspired from the workings of nature.
The primary pillars of the design process are understanding the environment, human factors,
modularity, and tiling. Understanding the environment comes first and foremost as architecture
of a place is dependent on its environment and we need to clearly define the problems that we
need to assess. Human factors help define the constraint or bounds within which the
architecture must be developed. Modularity helps in defining the abstract structure of the

habitat and enforces the rules through which the physicality of the habitat can be constructed.
Tiling is the geometric principle through which previous principles are brought to life and
provides a base to develop the architectural tectonics and materiality of the habitat.
2.1 The harsh environment
To design a high performant efficient habitat, it is important to understand the environment in
which we will operate. Extraterrestrial environments pose both physiological and
psychological challenges to humans. Some of the physiological stressors are changes in
pressure, extreme temperatures, environmental hazards of micrometeorites and radiation, loss
or alteration of time markers/ zeitgebers (an environmental agent or event, such as the
occurrence of light or dark, that provides the stimulus setting or resetting a biological clock of
an organism), irregular light cycles, noise and vibration, limited habitable space leading to
short focal distance stressed near-sightedness, poor ventilation, sterile and monotonous
surroundings, restricted diet etc. Psychological stressors include prolonged isolation and
confinement, reduction of privacy, the feeling of loneliness and separation from one’s normal
social group, dependence on a limited community, disconnection from the natural world,
limited leisure alternatives, etc. [20] The challenges are immense requiring expertise from
multiple fields collaborating with each other and a framework is required to effectively frame
our problem statement.
We have used NASA’s ‘RIDGE’ framework to identify the key area’s of focus that BHEEM
will address, thus establishing our brief for the design. RIDGE identifies five classes of human
hazards in space namely space radiation, isolation and confinement, distance from Earth,
gravity fields and hostile/closed environments [21]. BHEEM’s design focuses on isolation and
confinement and sets an architectural tectonic that can be scaled well with human activities.
Principles of ‘Astrotectonics’ (science of constructing space structures and facilities for use in
orbit) are used on manned voyages beyond Earth’s magnetosphere and for the creation lunar/
planetary habitats [22]. It embodies a variety of interrelated planning considerations like
requirements imposed upon elements and support systems by mission applications and
environments, transportation constraints determining allowable launch volume/mass, means
and support requirements to deploy the structures, and comprehensive operational demands
and circumstances that will influence utility and versatility. With a well-defined problem
statement, we can proceed to identify the right tools and design methods to effectively address
the problem.
2.2 Human Factors and Anthropometry
The many technical challenges for designing space habitation make it easy to overlook the
human factors considerations. Ill-designed spaces make it difficult for humans to efficiently
work and perform complex tasks with accuracy [23]. It may also lead to critical human errors
caused due to excessive fatigue [24]. The design methodology for BHEEM considers human
factors as the fundamental principle for habitat design.
One of the foremost important parameters we considered for an enclosed habitat is the volume
that is to be enclosed. This volume allows for all the activities to take place along with the
appropriate placement of relevant equipment, furniture, and life support systems. To be able to
determine the volume for various activities, we identified the activities that would take place
inside the habitat. The activities include tasks such as mission planning, habitat monitoring, or
extra-vehicular activity (EVA). Other activities such as meal consumption, exercise, and

dedicated hygiene areas are also important and are considered. The comprehensive list of all
the activities along with their broader categories are mentioned in the Appendix A.
Figure 1: Determining volume requirement for various activities using accurate CAD (Computer Aided Design)
model of astronauts. a) Volume requirement for personal hygiene related tasks such as – hand/face wash, self-
appearance viewing, shaving, etc. The approximate volume required is 1.2 cubic meters. b) Volume requirement
for EVA suit maintenance task that accommodates two astronauts and the suit to be serviced. The approximate
volume required is 4.8 cubic meters. c) Volume requirement for advanced medical care where two astronauts are
attending to one patient fully laid down. The approximate volume required is 5.8 cubic meters.
We used anthropometric computer aided design (CAD) human models (Figure 1) made for the
5th and 95th percentile measurements of the human body, referenced from NASA [25], to
calculate the volume requirement for each activity. For all the activities the CAD models were
placed in various body postures relating to the activity and the volume was measured keeping
sufficient clearance (~0.7m) along with the relevant furniture objects and equipment that is
necessary for the activity [25]. We obtained a comprehensive list of the various activities along
with their volume requirements, which gave precise categories of spaces that need to be
constructed. This forms the basis of the architectural design requirements for BHEEM ensuring
that human needs are met first.
2.3 Modularity as a principle
Modularity is a concept that has proved useful in many fields dealing with complex systems.
It is the idea of interdependence within and independence across modules. A module is a unit
whose structural elements are strongly connected among themselves and relatively weakly
connected to elements in other units. In other words, modules are units in a large system that
are structurally independent of one another but work together. The system as a whole must
therefore provide a framework – an architecture – that allows for both independence of
structure and integration of function [26].
For space architecture, modularity is quintessential in application. Already many projects have
been developed, deployed, and are still functioning that are based on the principle of modularity
[27]. ISS itself utilizes modular tectonics allowing for its assembly in space over multiple
launches and still proves to be an efficient model for extra-terrestrial habitation. For BHEEM,
we have utilized the segregated activities to form independent modules. The modules are
specifically made for a particular group of activities. The separation of activities in designated
areas is important as it allows for maximum efficiency of the individual activities [26]. These
modules function independently and have independent life support systems without any

reliance on other modules. The modules are interconnected through a system of hatches that
allow an individual module to be depressurized without having to depressurize the entire
habitat.
Figure 2: The various activities are clubbed together by determining which activities can share space and
equipment to form separate modules. Based on the volume requirement for each activity, the overall
minimum volume required for each module is determined. The volume for each module is written below
the module name. Activities that share sequential daily routine or tasks are joined together in the layout –
for e.g. the hygiene module and exercise module are connected to the private quarters. There is also an
overall separation between mission related modules (in red) and daily living modules (in green) that are
connected through the mission planning and private quarters modules.
To define the modules and their function, the volume measurement for each activity is
aggregated and grouped together based on activities that can overlap. For example, viewing
self-appearance, facial cleaning, oral hygiene, shaving, etc. happen in the same space with
similar furniture requirements, thus forming a set. Activities like urination and defecation form
a similar separate set, and shower or body cleansing forms another set. Since these sets of
hygiene-based activities are well grouped together and need to be separated from the rest of
the activities, the hygiene area is an independent volume. In the case of the hygiene area, the
volume requirement for each of these activities is aggregated into one taking the largest volume
required as the overall volume for personal hygiene [25]. By doing this for all the other
activities, we get distinct modules that logically connect with each other as shown in Figure 2.
On a broader level the modules are divided into those that are related to daily habitat living
with personal care (shown in green) and those related to mission required tasks and logistics
(shown in red). The volume requirement for each module is calculated based on the number of
permanent inhabitants and volume requirement for an individual inhabitant from the activity
data.
BHEEM’s modular approach provides many benefits. It allows for the structure to be
constructed from parts on-site while being efficient for transportation. The architecture is
flexible with the possibility of various layouts suited to the mission objectives and duration.
Our modular architecture enables space missions in multiple phases where each module works
independently of each other and expands with other missions during its lifetime. Subsequent
payload deliveries are possible for longer duration missions with smaller rocket payloads.
Failure of one component or module reduces the risk of catastrophic failure of the entire
mission. Independent modules allow for redundancy and backup in case of emergencies such
as fires or atmospheric leakages. Modularity provides sufficient options and time for decision
making during off nominal scenarios. It facilitates standardization of modules and components

for easy maintenance and replacement without having to stop or halt other functions. The many
advantages of modularity as a design principle make it an ideal choice for space architecture.
Tiling as the building blocks
Tiling allows for the physical embodiment for the abstract concept of modularity. The
geometric shape of a tile defines the function of the tile and how it will come together with
other tiles. It is important to consider how this shape affects the function. For BHEEM,
modularity with tiling happens at two levels – one is at the macro level where the layout itself
is a form of a tessellation with an underlying grid. The other is at the module level where each
module is composed of interchangeable panels that combine to form an enclosed space.
Figure 3: The concept of tiling. a) The triangle is one of the three regular polygons, other than squares and
hexagons, that can tesselate completely forming a regular tessellation that can grow endlessly b) Polygons
with same side length grow as the number of sides increases. c) The similar side length enables dierent
polygons to connect with one another seamlessly, aiding in a customized expandable layout that can grow
endlessly. In all three gures, the gradient fade represents the growth of the structures endlessly.
A tessellation is a pattern of shapes that fit together perfectly, without any gaps. They can be
formed from multiple regular or irregular shapes. Tessellations can be found largely occurring
in nature like hexagonal honeycomb, snakeskin, cellular structure of leaves or shell of a
tortoise, and have also been used in human architectural forms – from ancient Rome to the
present. The use of nature’s design principles for architectural applications in space hold great
potential for the future feasibility of the projects [28]. Some regular patterns tesselate very
easily while others do not tesselate at all. At every vertex of the tessellation, the internal angles
of the same or different polygon that meet at that point should sum up to 360o, otherwise there
will be a gap or an overlap. Figure 3(a) shows how a triangle can be tessellated infinitely to
grow into larger self. Similar results can be achieved with a square and a hexagon, all of them
making regular tessellations. In this design, all the polygonal shapes have a standardized side
length, which makes the junction between two modules seamless and perfect fitting. Another
property of regular polygonal shapes can be seen in Figure 3(b) where the size of the shape
depends on the number of sides. This corresponds to an increase in the surface area of the
horizontal cross section of the modules. These properties provide many advantages and are
utilized to plan the layout and influence the shape of BHEEM’s architecture.
Tessellations help maintain uniformity and help in better organization/planning. The
tessellations provide a grid on which the entire layout can be laid and planned. This allows for

an ever-growing colony that can adapt to a growing population as visualized in Figure 3(c). To
achieve this at the layout level with modular principles, the structure of the individual
components needs to interface well with each other while forming a tessellation.
At an individual component level, a collapsible structure is the most viable option for space
application since payload volumes and weight are a constraint. A habitat structure can be of
many types, each having their own advantages and disadvantages. Some of these structures are
conventional structures (rigid shell-like structure that is not collapsible), telescoping structures
(rigid structures that collapses by sliding one part into another like a telescope), inflatables
(flexible membrane based soft-body structures which expands upon inflating), origami-based
structures (structures having rigid plates with soft-flexible or hard mechanical hinge junctions),
or panel-based structures (made from multiple panels joining with each other) [29]. Most of
these structures need to be prefabricated here entirely on Earth, packed into a collapsed state,
sent to the desired destination and then deployed over there. For BHEEM, we utilize the panel-
based architecture as it uniquely provides the opportunity to have a modular system where the
construction and deployment of the structure can happen on site while the components and the
necessary tools are transported. There are other advantages to a panel-based structure as well.
Rigid panels allow for a wide range of materials to choose and iterate from. Any damaged panel
can be replaced easily, and a variety of shapes can be formed with the same panels. This panel
architecture also eliminates the need for any complex fabrication with easy to manufacture
parts. Tessellation along with modularity further provides concrete direction on how our parts
are designed.
Our methodology encompasses the process we used to conceptualize BHEEM’s design.
Understanding of the environment coupled with human factors considerations sets the
necessary constraints within which our structure is made. The design principle of modularity
along with panel-based tiling and tessellations makes BHEEM’s architecture efficient and
viable for space transportation and deployment. With the design direction established, we look
at the concrete aspects of design and how BHEEM can be realized.
3. Results
To keep the advantages of modularity, it is vital that there are maximum number of
configurations possible within a minimum number of unique components. Having minimum
components allows for easier replacement and easier logistics as compared to having too many
unique components. But at the same time, more unique components allow for more flexibility.
This balance must be maintained based on the use case at hand. A key component of the panel-
based architecture is the joinery that can connect all the panels together. The joinery also needs
to be versatile but without having too many variations. It is also the part that will take the most
amount of stress and thus is a critical component. To test the viability of our design we have
used numerical analysis to calculate the stress distribution on the panels and the joinery.
3.1 Module Design

Our methodology dictates for us to have a panel-based system that is based on regular
polygons all with the same side lengths. The best approach is to have simple panel shapes
that combine to form various polyhedral modules. The fundamental tiling shapes of triangle,
square, and pentagon are used for their simplicity, ease of manufacturing, and handling. With
just these three panel shapes we can generate a variety of polyhedral shape classes – Platonic
solids, pyramids, prisms, Archimedean solids, and many more.
The condition for having the polyhedral solids connect with each other in a modular way and
be laid out in a flat manner requires that these shapes be symmetrical in the plane in which they
are connected to each other. This allows us to use the square panel as the means to connect
various modules together. The module also provides sufficient space when deployed and take
the least amount of space when taken apart and stacked.
Figure 4: (a) Example of a joinery with 4-4-4-3 panel configuration. This shows that the joinery can attach panels
that have 4, 4, 4, and 3 sides all having side length of 2.5 m in a counterclockwise order. (b) The angle
configuration (81.6, 81.6, 71.1, 71.1) is the in-plane 2D angle that is formed between two consecutive flanges of
the joinery when projected on a plane in counterclockwise order. The panel configuration along with the angle
configuration can uniquely determine the joinery. (c) 1:12 scale model of a cube module of the habitat. This
structure is knock-down and follows the collapsibility principle of ‘Assembly’ [28]. It has 6 panel faces which are
made of MDF of 3mm thickness and fabricated by laser CNC. Each panel has a side length of 300mm. The
joineries (with panel configuration 4-4-4 and angle configuration 60o-60o-60o) have been fabricated using FDM
3D printing with PLA filament. The joineries and the panels are assembled seamlessly via nuts and bolts. The
purpose of this structure is to understand the junction between the panels and the joinery and their assembly
process.
The joinery is the key component that joins the panels together to form the modules. It encodes
all the information necessary to form the various shapes. The joinery is designed using
parametric modelling methods. For parametric modelling we calculated the joinery geometry

at each vertex. The individual flanges of the geometry are oriented and attached to a central
hub based on the normal direction of the panels connected to the vertex. The direction of the
central hub itself is taken as the average of all the normal of the connected panels. The final
geometry is generated by using a series of Boolean operations that allow for the panels to fit
together with each other and the joinery as can be seen in figure 4 (a).
Each joinery can be uniquely defined by specifying what panel shapes can be attached in what
ordered and the dihedral angles between the panels. A joinery with a panel configuration of 4-
4-4-3, as shown in figure 4 (a), signifies that the joinery can attach 3 square (4 sided) panels
and 1 triangular (3 sided) panel in a counterclockwise manner. The angle configuration of the
joinery, as shown in figure 4(b), signifies the in-plane 2D angle that is formed between the
direction vectors of two consecutive flanges as they lie on the plane. So, an angle configuration
of 81.6-81.6-71.1-71.1 for the same joinery represents the 2D angle subtended between the
square-square, square-square, square-triangle, and triangle-square plates. In figure 4 (c) we can
see how a fundamental cube module can be built with this system using panels and joineries.
We extensively explored possible polyhedrons that can be formed with the three panels-
triangle, square, and pentagon. Not all the polyhedrons are structurally stable and would
require internal pillar like structures to become stable which is not desirable for space
applications where volume optimization is of prime importance. Some of the modules we
listed are not well suited to be tiled with each other to form a modular layout, while some
don’t provide a volume expansion benefit when deployed. We identified 5 unique modules as
seen in figure 5 that can connect well with each other, are structurally stable on their own and
provide volume benefit when deployed. For the creation of the 5 modules, 7 unique joineries
are required with various panel and angle configurations.
As shown in figure 4 (a), a single panel has an edge length of 2.5 m in accordance with ESA’s
moon village report [30]. This has been taken considering the average height (1.8 m) of a
human. The ceiling height is required to be greater than or equal to 2.5m to avoid collision and
any contact while locomotion (slower walking, slower running with a tendency to slip, higher
and farther jumping, loping, etc.) or any of the other activities under the influence of reduced
gravity on Moon and Mars. The panel size of 2.5 m ensures that the smallest module shape also
has sufficient clearance for a human to stand and walk. Each panel has a depth of 0.2m to
accommodate for various layers of thermal, radiation, and MMOD protection. We have
calculated the volume of the module when it is disassembled by using the dimensions of the
panel. By looking at the stacked volume and comparing it with the deployed volume we obtain
how much volume expansion benefit each module provides. This varies for different modules
and the expansion is higher for modules that have a larger volume.

Figure 5: Creation of the module shapes with standardized panels requires unique joint configurations that connect
the panels at the vertices of the modules. Overall, 7 unique joints are required to form all the shapes. The color
coding shows which joint shape is attached to which part of the module shape. The panel configuration for each
joint determines which panels in what order are compatible with the joinery. The angle configuration is the 2D
planar angle between two consecutive flanges of the joinery. The stacked volume is the volume requirement when
the entire module is disassembled, and the panels are stacked on top of each other. Likewise, the deployed volume
is the interior volume of the module after being deployed.
3.2 Numerical Analysis
In designing module shapes and unique joints, structural analysis of critical components is
essential to understand stress distribution and deflection for ensuring the structural integrity of
each component. Thus, after identifying the unique shape of the modules and respective unique
joints, we proceed to finite element analysis of the entire assembly to understand how each
component behaves in actual loading conditions on Moon or Mars. Before analysing the stress
and deflection of the final assembly, it is essential to validate the solver and simulation setup

to check the accuracy of the generated results. For all our numerical analysis, we have used
Ansys 2024 R2 software which employs a finite element solver to calculate stress distribution
and deflection. We have carried out the validation of the solver and simulation procedure
considering two different cases and found out that our results have good agreement with the
existing experimental and theoretical results from the literature. The detailed explanation for
the validation cases is presented in Appendix B.
We first analyse the distribution of principal stress vectors on the joinery structure for a cube
joinery and an extended rhombicuboctahedron at maximum stress regions corresponding to
each unique module. In fig. 6, we illustrate the principal stress vectors for cube joinery and
extended rhombicuboctahedron joinery under the self-weight of a habitat subjected to
gravitational loading. We analyse principal stress vectors to depict the nature and magnitude of
the stresses experienced within these structures. The vectors are color-coded for clarity where
the blue vectors represent compressive principal stresses, and the red vectors indicate tensile
principal stresses. The magnitude of these stresses is conveyed through the length of the vector
arrows which gives a visual description of the intensity and distribution of forces within the
joineries.
In both the cube joinery (fig 6a) and the extended rhombicuboctahedron joinery (fig 6b), the
lower flange exhibits a concentrated distribution of stresses. This concentrated stress pattern
suggests that the lower flange is particularly vulnerable and may be prone to structural failure
under sustained gravitational loading. The accumulation of tensile and compressive forces in
this region indicates that it could be a critical point where material fatigue or failure might
initiate over time, especially in high-stress applications such as space habitats or structures in
extreme environments. In contrast, the other two flanges in both geometries show a different
stress behaviour. The tensile (red) and compressive (blue) stress vectors in these flanges exhibit
a more random or intermingled distribution, indicating a twisting effect within the flanges. This
intertwined pattern of stress vectors suggests that these flanges are subjected to torsional forces,
which could lead to complex deformation patterns and potential challenges in maintaining
structural stability. The presence of such twisting stresses implies that the design must account
for not only axial loads but also torsional effects to prevent unexpected structural issues.

(a)
(b)
Figure 6: The principal stress vectors on the joineries due to the self-weight of the habitat in gravity. The
blue vector represents the compressive principal stress, and the red vector represents the tensile principal
stress. The magnitude of the vector is represented by the scale of the vector arrow, (a) Joinery with highest
stress corresponding to cube module, (b) Joinery with highest stress corresponding to extended
rhombicuboctahedron module.
Overall, the comparative analysis of these joinery structures underscores the critical importance
of stress distribution in structural design. While both designs exhibit concentrated stresses in
the lower flange, which could be a potential failure point, the twisting observed in the other
flanges adds another layer of complexity to their mechanical behaviour. These insights are
essential for optimizing joinery designs, ensuring that they can withstand gravitational forces,
torsional stresses, thereby enhancing the overall durability and stability of the structure.

Figure 7: The first column shows the deflection for each module. Module d) shows the maximum deflection
at the centre with a value of 6.6e-4m. The second column shows the von-mises stress distribution for the
whole module with the joinery attached with bolts modelled as beam elements. The third column shows
the von-mises stress distribution for the joint that has the maximum stress for that module. The maximum
von mises stress subjected to a joinery is for module d) with a stress of 725 MPa.
Next, we proceed to analyse the deflection and stress distributions on the five unique modules
namely cube, cuboctahedron, rhombicuboctahedron, extended rhombicuboctahedron, and
modified rhombicosidodecahedron along with their respective joineries. We use the similar
numerical procedure in Ansys 2024 R2 software to simulate the deformation of the structures
where only the gravitational force is involved. We are here interested in looking at the effects

of gravity on our structures to determine the structural stability of various modules. For
simulating each unique module, a sufficiently fine mesh is generated to eliminate the
dependence of mesh resolution on calculated results. It is worth mentioning that the bolt
elements which connect the plates to the joinery are modelled as beams which can accurately
replicate the geometrical bolts in cases where stress and deflection analysis of the joinery are
of prime importance. Employing the finite element analysis, we identified the region of
maximum deflection and maximum stress for various modules and joinery as presented in fig.
7. The contours of Von Mises stress distribution and deflection helps us understand the
structurally critical regions. From fig. 7 it is evident that the high stress regions are generally
formed at the joints in the vicinity of the bottom of each module. From the finite element
analysis, the extended rhombicuboctahedron configuration shows a maximum deflection of 6.9
mm which is the highest deflection as compared to other configurations. Similarly, the
maximum Von Mises stress is observed for the extended rhombicuboctahedron configuration
at its bottom joinery which is approximately 393 MPa. Thus, from the above analysis, we can
conclude that the maximum Von Mises stress (393 MPa) observed in our configurations is well
below the yield strength of typical space grade Titanium alloy (approximately 1200 MPa) [31].
It is important to note that, the present FEA analysis considers the Titanium alloy as the material
for the panels which are solid in nature. However, in actual conditions the panels will be made
with hollow structure. Thus, our present analysis serves as a limiting case scenario for analysing
the structural rigidity of the proposed modules and joineries.
3.3 Layout and Packing
A monolithic habitat usually has all the necessary facilities inside the same structure with
effective partition. BHEEM’s design has a modular structural system where each structure or
module facilitates a particular space for different activities. This allows for the creation of a
flexible layout that can accommodate various mission needs. As an example, we will
demonstrate how BHEEM’s architecture enables the creation of an extra-terrestrial base for a
crew of 16 and a duration of more than 6 months.
One aspect for the designation of each module shape for specific activities is the volume
required by each activity. From Figure 2, we can see that the private crew quarters for 4 people
require a habitable volume of 60m3. Hence, 1 person would require a volume of 15m3. One
cuboctahedron provides a lateral volume of 31m3 which is sufficient to accommodate 2
inhabitants. Therefore, we can accommodate 16 inhabitants in 8 cuboctahedron modules.
Another aspect is the overall shape and it’s fit for the activities. A private crew quarter needs
to cater to the privacy of the inhabitants as well. Hence, the cuboctahedron is ideal since it can
allow for the private accommodation of 2 inhabitants with minimal room dividers and sufficient
wall surfaces to accommodate various interior furniture equipment.
The layout of our habitat has been carefully designed keeping in mind the active and passive
interactions, the frequency of use of the spaces, and the distances between modules. The
modules can be connected to each other with the cube module that functions as a passageway.
This modular deployment allows for a stagewise expansion as the duration extends and mission
objectives evolve. Fig. 8 shows the various stages of deployment and expansion of the habitat
layout as the mission progresses. The 1st stage includes the deployment of the base module
which is the common work quarter. Here, most of the mission related activities will be
performed. This space will accommodate 5 individuals with ease. It is the first one to be
deployed because all other spaces will emerge from this and will be accessible from this. All

common group work related activities such as video conferencing with the Mission Control
Centre on Earth, deskwork etc. would be done from here. Right after deployment it would also
act as a temporary sleep station for the inhabitants until the 2nd stage where the private crew
quarters would be deployed. Apart from these, here the inhabitant would also monitor the
habitat systems and conduct teleoperations. This module has two attachment modules: one is
the lavatory module for toilet purpose (no shower or grooming) and waste disposal system,
accommodating 4 individuals at a time, and the other one would be an airlock for
pressurization/ depressurization, EVA suit maintenance and extravehicular activity that can
accommodate the suits and equipment of 8 astronauts.
In the 2nd stage the private crew quarters would be expanded. It would bifurcate into two wings,
each of which will consist of a central module where group activities like dining, meal
preparation, exercise, recreation, etc. will happen. There are 4 sleep stations in either wing,
each of which can accommodate 2 inhabitants and provide stowage space for their personal
items. There are 2 hygiene modules in each wing which will facilitate shower, grooming, toilet
and a waste disposal system, and will accommodate 4 individuals at a time. The private crew
quarters will be connected to the common work quarters via tunnelways.
In the 3rd stage, modules for stowage of equipment and ration would be attached from the
central work quarters. Equipment like robotic systems, communication devices, basic tools,
etc. and ration for 6 months at least could be stored.
In the 4th or the final stage, the experimental laboratories for biological and physical sciences
would be attached. In the bio-sciences division, a greenhouse is also added for controlled
cultivation of crops. Apart from that another module is attached for medical purposes of
diagnosis and treatment and surgery.
Figure 8: Proposed layout with stages of mission expansion. a) Base module (Common work quarter) with
computers and robots for teleoperations, airlock for EVA and hygiene module attachments. b) Addition of

private crew quarters for sleeping, meal preparation and dining, exercise and recreation. c) Addition of a
stowage module for storing equipment and ration. d) Addition of dedicated laboratories for physical and
biological science experiments along with a greenhouse for controlled agriculture.
The habitat from a macro perspective has a minimalistic design with simple modular
permutations and combinations of structural modules made of very simple geometry. But due
to its simplicity, it addresses complex issues of transportation and logistics. Figure 9 presents
a visualization of BHEEM on a Martian environment. In this render, we have shown the habitat
supported by means of hydraulic legs, mounted on the underside, to account for the height
differences of the various modules and seamless junction of two modules. Apart from that, it
also allows the habitat to be levelled despite undulation of the topology. There are staircases
deployed to facilitate EVA by allowing the astronaut to land onto the ground from the habitat.
There is communication devices mounted on the top of the central module to facilitate
communication with Earth, and radars to monitor meteorological events. There are unmanned
rovers that can be teleoperated from the habitat or run autonomously. An astronaut is presented
along with the habitat and one of its modules to give a sense of scale.

Figure 9: a) Conceptual 3D render of BHEEM on Mars with various modules combined to form a large permanent
habitation. b) Standalone module made by joining modular panels.
The habitat when deployed on site provides a total volume 2130 m3. But transporting that much
of a volume with the technology of today is clearly impossible [12]. Even with the mighty
starship, it would take a tremendous number of launches to take it to the destination. To tackle
this challenge, the entire habitat is designed keeping in mind its collapsibility feature to be
accommodated inside a rocket payload volume. The collapsibility principle of assembly [32]
is being applied here. Figure 10 shows how our entire proposed layout of the habitat can be
accommodated inside the payload fairing volume of a Starship. The versatile habitat can be
packed in multiple types of vehicles and is not restricted to any single type. Although here in
this figure, this volume accounts for only the panels. The other components like joineries,
interior and exterior elements would require another launch.

Figure 10: The proposed layout requires 312 square panels, 108 triangular panels, and 2 pentagonal panels for a
total of 422 panels. The approximate stacked volume required for all the panels is around 700 cubic meters. The
proposed layout can be entirely stacked in a single payload of the Starship (volume of around 800 cubic meters)
with all 422 panels that are required.
Discussion
BHEEM’s design in the current state has scope for many improvements and future scope of
work. The design presented in the paper is the initial direction to pave the way for India’s extra-
terrestrial habitat system. The materiality of the panel design is one of the key areas where
substantial future research is planned. Sealing of the habitat within and in between the panels
is the next problem that can be tackled. A double redundancy system with soft inflatable could
be proposed to be installed inside the outer hard shell once it is deployed. This would ensure
that in times of off-nominal scenarios, such as a pressure leakage due to cavity formation in the
outer shell or internal inflatable, the atmosphere is contained and provides ample time for a
quick repair. The testing of habitability using AR/VR technologies will also be beneficial along
with the creation of full-scale mock-ups. The addition of a safe-haven system that extends from
the current architectural morphology is planned that would allow inhabitants to take refuge
deep underground in cases of harsh atmospheric conditions. The current architecture can also
expand to multi-storey modules allowing for the creation of mega-cities in the future.

Figure 11: A soft inflatable will be installed inside the panel enclosure to provide redundancy for the risk of air
pressure leakage due to unanticipated cracks or cavities in the structure during off-nominal scenarios. In scenarios
where there is an event where the inflatable is punctured from the outside, the exterior enclosure would contain
the atmosphere. Hence, both structures together provide redundancies against loss of atmospheric pressure.
Conclusion
BHEEM is one of the first steps towards establishing a long-term human base on the harsh
extra-terrestrial environments of the Moon or Mars. The habitat has been designed with first
principles and using the human-centred design approach. By considering the volume
requirement for all activities, the habitat allows for sufficient volume making mission
objectives efficient and more astronaut friendly. The combination of 3 types of unique panels
and 7 types of unique joinery allows for several modules to be made that provide a flexible
layout which can evolve during the lifetime of the mission. The modular architecture makes it
feasible to transport the habitat in rocket payloads of lesser capacity making transportation
cheaper and the logistics easier. Our proposed layout (Figure. 8 (d)) can be accommodated in
a single payload of the starship, discounting other peripherals, and provides twice the volume
of the ISS. The joinery system encodes the shape of the modules and supports the entire weight
of the habitat. The architectural tectonic design is just the beginning direction for BHEEM and
there are many technical challenges to be solved.

Appendix A
Table A1: Segregation of the various volume requirement into modules with the relevant activities. The
volume requirement is in cubic meters calculated for a crew of 4 people.

Appendix B
We have carried out the validation of the solver and simulation procedure considering two
different problems. In the first validation case, we consider a bolt which is subjected to varying
pretensions (6 kN and 17 kN) applied to two parts as illustrated in the schematic fig. 6(a)
following the paper [33] and compared results for bolt force and separating force with the
existing experimental data. We obtained the error percentage for varying normalized external
force by comparing the experimental and our numerical data which are presented in fig. 6(b).
It is evident from the figure fig. 6(b) that, our finite element simulation results show a good
agreement with the existing experimental results from literature with a max 0.63% of relative
error. Furthermore, in the second validation case, we consider a standard configuration where
a plate is simply supported at each corners following the paper [34], the schematic of which is
presented in fig. 6(c). We consider such a configuration for validation because, our structure
along with the joinery are plates that are supported at the corners by joinery which shows close
resemblance with the considered validation case. We obtain the relevant equations and constant
for various ratios of side lengths (a/b) from [34] that allows us to analytically calculate the
deflection. We have carried out the numerical simulations with corner supports on plates and
measure the deflection of the panel at the centre. In fig. 6(d) we present the comparison of
relative errors calculated for analytical result and our simulation result for varying aspect ratio
(a/b) of the plates. It is evident from the figure that both the analytical and numerical results
have a very good agreement for various aspect ratios with a maximum relative error of 3.7%
corresponding to (a/b = 4). The above discussion on validation cases clearly demonstrates the
accuracy of the solver and simulation procedure to calculate forces and deflection in the
structures.

Figure B1: (a) schematic of the rst validation case where a bolt which is subjected to varying pretensions
is considered, (b) bar chart showing the variation of percentage error with normalized external force for two
dierent values of applied pretension, (c) schematic of the second validation case showing a plate which
is under the application of uniform gravity and simply supported at each corner, (d) bar chart showing the
variation of percentage error with varying aspect ratio of the plate.
References
[1] Baker, Phillip. 2007. Review of Salyut 6: Space Station Operations Defined. In The
Story of Manned Space Stations. Springer, New York, NY: Springer Praxis Books.
[2] Baker, Phillip. 2007. Salyut 7 and Spacelab. In The Story of Manned Space Stations.
Springer, New York, NY: Springer Praxis Books.
[3] Robinson, Douglas K.R., Glenn Sterenborg, Sandra Häuplik, and Manuela Aguzzi.
2008. “Exploring the Challenges of Habitation Design for Extended Human Presence
beyond Low-Earth Orbit: Are New Requirements and Processes Needed?” Acta
Astronautica 62 (12): 721–32.https://doi.org/10.1016/j.actaastro.2008.01.034.
[4] Jackson, Keegan, Frances Brewer, Ashley Wilkinson, Amari Williams, Ben
Whiteside, Hannah Wright, Lynn Harper, and Anne M. Wilson. 2023. “Microgravity
Crystal Formation.” Crystals 14 (1): 12. https://doi.org/10.3390/cryst14010012.
[5] Ulises Rojas-Alva, and Grunde Jomaas. 2022. “A Historical Overview of Experimental
Solid Combustion Research in Microgravity.” Acta Astronautica 194 (May): 363–75.
https://doi.org/10.1016/j.actaastro.2022.01.037.
[6] Cubo-Mateo, Nieves, and Michael Gelinsky. 2021. “Wound and Skin Healing in
Space: The 3D Bioprinting Perspective.” Frontiers in Bioengineering and
Biotechnology 9 (October). https://doi.org/10.3389/fbioe.2021.720217.
[7] Puhl, Christopher, Nicol Caplin, Anna Fogtman, and Angelique Van Ombergen.
2022. “Wound Management and Healing in Space.” Frontiers in Bioengineering and
Biotechnology 10 (August). https://doi.org/10.3389/fbioe.2022.958515.
[8] Santhoshkumar, P., Aditi Negi, and J. A. Moses. 2023. “3D Printing for Space Food
Applications: Advancements, Challenges, and Prospects.” Life Sciences in Space
Research, August. https://doi.org/10.1016/j.lssr.2023.08.002.
[9] Gensler, Marius, Anna Leikeim, Marc Möllmann, Miriam Komma, Susanne Heid,
Claudia Müller, Aldo R. Boccaccini, Sahar Salehi, Florian Groeber-Becker, and Jan
Hansmann. 2020. “3D Printing of Bioreactors in Tissue Engineering: A Generalised
Approach.” Edited by Yi Cao. PLOS ONE 15 (11): e0242615.
https://doi.org/10.1371/journal.pone.0242615.

[10] Jones, Harry. 2018. “The Recent Large Reduction in Space Launch Cost.”
https://ntrs.nasa.gov/api/citations/20200001093/downloads/20200001093.pdf.
[11] “Are Space Scientists Ready for Starship—the Biggest Rocket Ever?” 2022. AAAS
Articles DO Group, August. https://doi.org/10.1126/science.ade3377.
[12] Review of Starship User Guide. 2020. SpaceX.
[13] Arnold, Jim, Eric L Christiansen, Alan Davis, James Hyde, Dana Lear, J.C Liou,
Frankel Lyons, et al. 2009. “Handbook for Designing MMOD Protection.” Nasa.gov.
January 28, 2009. https://ntrs.nasa.gov/search.jsp?R=20090010053.
[14] Benaroya, Haym. 2018. Building Habitats on the Moon: Engineering Approaches to
Lunar Settlements. Cham, Switzerland: Springer.
[15] Radiation Answers. 2019. “Effects of Radiation.” Radiation Answers. 2019.
https://www.radiationanswers.org/radiation-and-me/effects-of-radiation.html.
[16] Valle, Gerard, Doug Litteken, and Thomas Jones. n.d. “Review of Habitable
Softgoods Inflatable Design, Analysis, Testing, and Potential Space Applications.”
https://ntrs.nasa.gov/api/citations/20190000847/downloads/20190000847.pdf.
[17] Ekblaw, Ariel, Elisheva Shuter, and Joseph A Paradiso. 2019. “Self-Assembling Space
Architecture: Tessellated Shell Structures for Space Habitats.” AIAA Scitech 2019
Forum, January. https://doi.org/10.2514/6.2019-0481.
[18] “Moon Village.” n.d. Www.esa.int.
https://www.esa.int/About_Us/Ministerial_Council_2016/Moon_Village.
[19] Koshy, Jacob. 2023. “PM Modi ‘Directs’ ISRO to Land Man on Moon by 2040.” The
Hindu, October 17, 2023, sec. Science. https://www.thehindu.com/sci-
tech/science/pm-modi-directs-isro-to-land-man-on-moon-by-2040/article67431169.ece.
[20] Häuplik-Meusburger, Sandra, and Sheryl Bishop. 2021. Space Habitats and
Habitability. Springer Nature.
[21] NASA. 2019. “The 5 Hazards of Human Spaceflight.” NASA. 2019.
https://www.nasa.gov/hrp/hazards/.
[22] Review of Astrotectonics: Construction Requirements and Methods in Space. 1989. In
SICSA Outreach. Houston: University of Houston.
https://sicsa.egr.uh.edu/sites/sicsa/files/files/publications/astrotechtonics.pdf.
[23] Gavriel Salvendy. 2012. Handbook of Human Factors and Ergonomics. Hoboken,
N.J.: John Wiley. [2.2]
[24] Scheuring, Richard A., Jeffrey A. Jones, Joseph D. Novak, James D. Polk, David B.
Gillis, Josef Schmid, James M. Duncan, and Jeffrey R. Davis. 2008. “The Apollo
Medical Operations Project: Recommendations to Improve Crew Health and

Performance for Future Exploration Missions and Lunar Surface Operations.” Acta
Astronautica 63 (7-10): 980–87. https://doi.org/10.1016/j.actaastro.2007.12.065. [2.2]
[25] Stromgren, Chel, Callie Burke, Jason Cho, Michelle A Rucker, and Maria Garcia-
Robles. 2020. “Defining the Required Net Habitable Volume for Long-Duration
Exploration Missions.” ASCEND 2020, November. https://doi.org/10.2514/6.2020-
4032. [2.2]
[26] Baldwin, Carliss Y, and Kim B Clark. 2000. Design Rules. The MIT Press EBooks.
The MIT Press. https://doi.org/10.7551/mitpress/2366.001.0001.
[27] Hu, Gangxuan, Yanyan Li, Xinhong Li, Guohui Zhang, Zhibin Zhang, Xun Wang,
and Wanxin Man. 2023. “Modular Self-Reconfigurable Spacecraft: Development
Status, Key Technologies, and Application Prospect.” Acta Astronautica 207
(March): 240–56. https://doi.org/10.1016/j.actaastro.2023.03.012.
[28] Gruber, Petra, and Barbara Imhof. 2007. “Transformation: Structure/Space Studies
in Bionics and Space Design.” Acta Astronautica 60 (4): 561–70.
https://doi.org/10.1016/j.actaastro.2006.09.032.
[29] Bell, Larry. n.d. “Part 1: Space Structures and Support Systems SISCA Space
Architecture Seminar Lecture Series.”
https://sicsa.egr.uh.edu/sites/sicsa/files/files/lectures/space-structures-and-support-
systems.pdf.
[30] Review of CFD Study Report Moon Village Conceptual Design of a Lunar Habitat.
2020. Netherlands: European Space Agency.
[31] Anil Kumar, V., R. K. Gupta, M. J. N. V. Prasad, and S. V. S. Narayana Murty.
2021. “Recent Advances in Processing of Titanium Alloys and Titanium Aluminides
for Space Applications: A Review.” Journal of Materials Research 36 (3): 689–716.
https://doi.org/10.1557/s43578-021-00104-w.
[32] Per Mollerup. 2002. Collapsibles : A Design Album of Space-Saving Objects. San
Francisco, Calif.: Chronicle ; London.
[33] Williams, J.G., R.E. Anley, D.H. Nash, and T.G.F. Gray. “Analysis of Externally
Loaded Bolted Joints: Analytical, Computational and Experimental
Study.” International Journal of Pressure Vessels and Piping 86, no. 7 (January 30,
2009): 420–27. https://doi.org/10.1016/j.ijpvp.2009.01.006.
[34] Al-Shugaa, Madyan A., Abubakr E. S. Musa, and Husain J. Al-Gahtani. “Analysis of
Corner Supported Plates Under Symmetrical Loading.” Arabian Journal for Science
and Engineering 44, no. 10 (March 23, 2019): 8707–15.
https://doi.org/10.1007/s13369-019-03811-z.