The design of a marine habitat is one of the most horrifying and incredible experiences that an engineer could have. Although such harsh environments such deep space or the Arctic tundra have their own amazingly complex and difficult development issues, the deep sea has long been considered the most unknown and difficult terrain for man to conquer. To introduce a longer term prototype habitat for a sustained underwater human community, I decided to use skills that I developed from my engineering dual enrollment classes to design a facility that could hypothetically be a modular, deep sea habitat.

Cement

Rebar

Titanium

Steel Alloy HY-100

Glass

Acrylic

Goals

1. To develop a structure capable of withstanding long-term (muli-month, multi-year) stresses and material fatigue.
2. To create a habitat capable of sustaining longer-term independent human habitation, such being able to grow crops, synthesizing breathable air, being able to sustain normal human development, and being expanded to cover a longer area.

A summary of the different challenges that a marine structure faces:

In consideration of the pressure that the marine structure faces, it is firstly important to determine force the water surrounding the structure will exert upon the structure. For example, at a specific depth of 200 meters (appr. 650 ft), the pressure upon an object would be approximately 196 Psi, an enormous amount of pressure. As such there are few materials that normally chosen. Namely, the material of choice when building submersibles seems to be titanium, however, when examining other aquatic boats and platforms, such as nuclear submarines, deep-sea oil rigs, and already existing marine habitats, such Aquarius, operated by the Florida International University), it becomes apparent that there are other possible building materials such as certain alloys of steel such as HY-80 or HY-100, which might also be able to be used.

In consideration of the amount of light that would be advisable for human activity and exploration (whether by vehicle or by diving), the area would have to have visible light, limiting the either the epipelagic zone (from ocean surface to approximately 200 meters) or edge of the mesopelagic zone (from (200m to 1000m). Although we have had the technology to create vessels able to dive deeper than 10000 meters for nearly sixty years, never before has a long-term research and colonization habitat been created to operate at these depths. As such, as a stepping stone, a reasonable first habitat should be able to operate at a depth where divers and many submersibles should be able to operate.

In consideration of the location that would be optimal for energy production, proximity of major trade routes, and seismic activity, there are many possibilities. However, in order to meet the challenge of (hopefully) being able to produce energy without a constant need for refuel from surface transports, the location should either be in relatively close proximity to oceanic geothermal vents (OGVs) or near strong ocean currents. While these do add additional complexities due to the possible seismic activity near some OGVs and the dangers of having a 30,000,000 cubic meters of water per second current flow (Gulf Stream’s flow rate through the Florida Straits) through a structure designed for human habitation. In addition, the proximity of major shipping lanes would unduly cause a constant disturbance in the waters surrounding the habitat, in addition to providing a bias in research operations due to the influence of shipping vessels on marine life. Finally, the location should not in an area so seismically active that a high magnitude earthquake will knock the habitat itself from its foundation and pilings.

In consideration of the all these conditions, there is now the trick of determining which conditions will play into each other’s favor and which ones will be at complete odds with each other.

To summarize: because the marine environment varies so wildly, let us determine specific conditions that are to be met:

1. The depth of the habitat is fixed at 200 meters (appr. 650 feet) in the ocean. The reason that this depth was chosen was that this is the end of the sunlight or photic zone, the highest of the four main marine zones. This region is the only one of the four that has sunlight permeating its lowest depths. A structure below this depth would not only have to deal with catastrophic amounts of water pressure, but also have to deal with a complete lack of sunlight (sunlight does not penetrate the depths past around 200 meters), in addition to having far fewer vessels that could reach the habitat should something go wrong. In addition, it has been proven that in the event of habitat failure, it has been proven that humans could survive and reach the surface, assuming use of diving equipment.
2. The habitat should be made up of modules that would allow the habitat to expanded should further colonization be able to be continued or to be shrunk should modules fail. By having a flexible format, similar to the International Space Station or multiple NASA Mars habitat concepts (MARS EMC habitat approach), different areas of the habitat can be placed as needed and replaced as necessary, allowing repairs to be taken without requiring the surfacing of the entire structure.
3. The habitat should be able to have living space and facilities for an adaptable number of people, with the minimum crew necessary being seven. The habitat should be able to be placed in a location that is able to have a maximum and minimum temperature where the structure’s frame is able to deal with, the possibly dramatic, changes in temperature as well as the corresponding change in water density and other factors, such as unexpected earthquake shocks or effects from tsunamis.
4. The location of the structure should be away from areas of high seismic activity, which could affect stability and build of the structure, or at the very least influence the design of the base of the habitat; ideally, this habitat would be placed relatively close to some large landmass, either a large island or at least a peninsula.
5. The structure’s proximity to major trade routes and ports should be minimized, due to the effects of having ships cause fluctuations in the water around the habitat, and for the obvious reason of having large vessels over an experimental manned habitat is not advisable.
6. The habitat, using either oceanic thermal vents, oceanic currents, or nuclear power, should be placed in an environment where its one source of power can be reliably depended on. 
7. The habitat should be organized in such a way that the living spaces are relatively comfortable for necessary and recreational human activity, such as research, exercise, de-stressing, eating, rest, experimental agriculture, elimination of waste, recirculation of air, and other activities.

In order to meet the guidelines listed above, it was decided to develop a modular, saltwater habitat based off of a NASA Mars habitat design, using the specifications above and some of the additional requirements listed in the 2018 paper Advantages of a Modular Mars Surface Habitat Approach. While some of the conditions listed in the paper do not apply to this project, it does provide an important resource for any extreme environment design. Namely, by utilizing a modular design, the amount of time and money is decreased per each capsule, and the room for error is slightly greater than for a larger “monolithic” design, where a single, minor error could mean that the entire large environment is jeopardized or be scrapped. In addition, because of the long-term nature of the habitat in an environment that is a harsh, unforgiving terrain with constant chemical attacks from salt on materials, fatigue and endurance limits always a possibility of being tested, and the possibility of rescue or repair would most likely take longer than threatened occupants would have.

As such, this design calls for at least 8 modules with a pressure hull thickness of .27 meters (appr. 10.6 in) to be the minimum number for a fully-operational base with additional modules being able to be added to provide greater research capacity, additional recreational facilities, or observational sites. The modules initially necessary would include:

• A energy production module housing a nuclear reactor similar to that aboard nuclear submarines
• A main “hub” module for the fraternization and socialization of the crew, in addition to the central controls for all modules, including life support, gas monitoring, radiation observation, and communication
• A living/washing facilities module for the crew members as well as the secondary controls for the habitat
• A moon pool and saturation diving conditioning module for manned diving
• A “hanger” module for the launch of manned and unmanned submersibles and research devices
• A fabrication room for the usage of repairs and development of devices
• A greenroom module for the growth of the sustainable plant life
• A storage module for the inevitable amount of supplies that must be preserved.

Although the habitat could be operational without at least three of the modules, the number allows for a great deal of variety of modular placement options and a range of operations. The location proposed for such a habitat is either on the edge of the Australian Continental Shelf, close to Hawaii, off the coast of Texas in the Gulf of Mexico, or off the coast of Guadeloupe, with special preference given to the Gulf of Mexico location. This location is recommended due to the plethora of existing facilities that have experience in building large marine structures, specifically offshore oil rigs. By developing the habitats modules in this area and having geological and civil engineers who are comfortable in that region, research and development costs for preparing the seabed for the arrival of the habitat could be minimized.

Research for Design

After using the following resources, the guidelines were created and developed into the following points:

Resources: 

The New Yorker’s article “Thirty-Six Thousand Feet Under the Sea” by Ben Taub

Scientific American’s article “See How Crushing Pressures Increase in the Ocean’s Depths” by Sophie Bushwick

Howstuffworks’s article “How Submarines Work” by Marshall Brain & Craig Freundenrich, Ph.D.

Howstuffworks’s article “How Is Oxygen Made Aboard a Spacecraft?” by Craig Freundenrich, Ph.D.

NOAA’s article “How Does the Temperature of Ocean Water Vary”

Woods Hole Oceanographic Institution’s “Sunlit Zone”

The Navel Post’s article “How Safe the U.S. Nuclear Powered Warships?” by Mehmet Cem Demirci

The Office of Energy Efficiency and Renewable Energy (Department of Energy)’s article “Enhanced Geothermal Systems”

The Constructor's "Concrete Exposed to Seawater - Effects and Preventions"

A host of Youtube videos including the following:

The Making of the Deep Submergence Vehicle (DSV) Limiting Factor - Documentary by Nick Verola posted by Caladan Oceanic

How Do Nuclear Submarines Make Oxygen?- Smarter Every Day 251 posted by SmarterEveryDay

Aquarius Reef Base | JONATHON BIRD’S BLUE WORLD posted by BlueWorldTV

ASC Live : Locations for Underwater Habitats posted by ASC

Skyscraper at Sea - Building the Amazing Appomattox posted by Shell

Extreme Subsea Engineering - Shell’s New Vito Platform | With Kari Byron of MythBusters | Ep. 2 posted by Shell

From these resources and many additional ones, the following conclusions could be drawn:

• It would be feasible that using current technology a long-term underwater habitat could be built
• The location to be build such a facility does exist (off the coast of Texas) and could be located not far from existing deep-sea facilities such as oil rigs, other existing habitats, shipyards, and marine research centers. By positioning the habitat in this environment, the time to reach the habitat from the shore with a vital replacement part could be minimized, possibly saving the entire habitat from collapse. In addition, by having shipyards and a deep-water port near by means that if there were a serious enough problem, the entire habitat is small enough to be moved by transport vessels to a facility that could repair it.
• The materials to build such a habitat could be high-strength Portland cement, HY-100 steel alloy, titanium, acrylic, glass. The reason for using Portland cement is that it is one of the most common cement mixes in usages such as foundations for offshore oil spars, bridges, and other structures that are constantly attacked by the strong chemicals in seawater; in addition, it is able to set in water, and retain its strength for long periods. HY-100 is a steel alloy that was first used to build the Seawolf-class of nuclear submarines. Although titanium is a more common building material for non-military submersibles and some existing habitats, its rarity would pose a problem for a structure that would much larger than many of the existing projects, and the current supply of titanium may not be enough for the hull and superstructure of the habitat. As such, titanium would be used to create the pressure hulls of the individual modules, while the main hub would have its pressure hull made out of HY-100. As for the use of acrylic and glass as transparent porthole materials: both materials have been used to create windows for existing habitats, and as for as I could research, there was not necessarily a large improvement of using one over the other at the depths that this facility would be operating. Of course, at deeper depths, the number of windows would likely decrease due to the pressure increasing and the issues that could arise from the structural stability of either material.
• The habitat could be built in pre-existing facilities that contract to offshore oil rig or wind companies companies.
• The energy resource to power such a facility does currently exist and has a proven track record of having few to no accidents in similar settings (nuclear reactors aboard nuclear submarines).
• The human physique can withstand the pressures at which the habitat will be operating and in a pressurized environment can survive for extended periods of time, although the maximum length of time the body could be survive in such an environment is uncertain. The longest period so far that anyone has lived in a pressurized environment without depressurizing (returning to the surface) has been seventy-four days, a record held by a biomedical engineer in Jules’ Undersea Lodge. (BBC, Florida Professor Breaks Record for Time Spent Underwater). It is actually this project, Project Neptune) that this professor was part of that will most likely be the best source of research about how the human body will react to living underwater for months at a time.

The final design involved putting all of the individual modules together and attaching together. The main modules are all located on the main (1st) floor deck, simply, because it allows the largest amount of modules to be attached to it by the size of its diameter. Although there are certainly other configurations this one seemed to be the best orientation. In addition, though main material of the design of the main hub is glass, this was intentional, since it would allow the viewer to examine the different floors and determine the orientation and layout of the habitat; however, the shell of the hub would most likely be made out of the steel alloy HY-100, due to the fact that having so much glass at such depths of 200m with a pressure of over 196 MPa would not be advisable from a structural design perspective. HY-100 is a steel alloy that was used in the design of multiple US Navy Nuclear submarines, and while possibly having some welding design issues, this did not seem to be a serious enough issue not to use it for this project, especially since producing enough titanium to build the entire habitat would be quite difficult given titanium's relative rarity. The main base of the habitat sits on a 10 meter thick slab of Portland concrete, in order to provide a secure foundation for the base, while the nuclear reactor module actually has its own base and stabilizers since its stability would be a top concern.

This project helped me use main of the engineering skills I learned in my dual enrollment classes in a university and also allowed me to use elements of a project that I presented at the university's research conference. In addition, it helped me realize that building structures (not as complicated as this) is possible even without an incredible amount of funding. I have been inspired to take advantage of opportunities around to use my local maker's space and start building devices and structures that I can now take from design to production. Ultimately, it was fascinating to learn about how the sea is still one of the most unexplored areas of the human environment, and while examining current and projected designs that take into consideration factors such as a rising sea level, I learned more about humans' long, difficult relationship with the sea. Given what we do know, however, about the threat of submersion that coastal dwellings are currently facing, in my opinion, it seems that underwater habitats and the development of should be one of the foremost engineering and architectural goals.