Living on the Seafloor. (Design Issues on Underwater Habitats. 4th part). The Habitat and Support Systems

Structure and Materials [9]
Open bottom habitats with moon pools will have the same internal and external pressure for the air to push the water out of the habitat. The structural design is not as complex as the closed habitats for large depths, but decompression is normally accomplish within the habitat and differential pressure between the internal compartments and the exterior will exist.
The most efficient structural arrangement to support hydrostatic pressure resists the loads by direct stress without loss of stability or buckling. Spheres are the most efficient shapes for high depth but very difficult to manufacture and the space for the arrangement of internal systems could be a problem. Cylinders with ring stiffeners provide a better arrangement for distribution of the space without making the external walls to thick and heavy.

Blueprints fo the Deepcore II. From the movie The Abbys

For structural integrity the more important aspects are collapse strength or the resistance to the hydrostatic loads, the dynamic loads and fatigue, but materials, weight, corrosion resistance and method of fabrication will play an important role on the design of the structure and components. Basic structures can be attached together to form different compartments as modules for different purposes.
The end closures and opening in the shells are considered week points; the reinforcing and seals next to the openings, hatches, viewing ports and hull penetration couplers or instruments, needs special attention on design and construction. Safety factors have to be carefully established for the materials and structural design.
As the habitat will be a compartment full of gases, buoyancy of the structure is controlled by the weight, anchoring the habitat to the seafloor and ballast. For an open bottom habitat with aquanauts in saturation, the rapid ascend of the habitat to the surface because a positive buoyancy and lost of ballast, will represent dead of the occupants.

Breathing Gases [10]
For longer stays underwater and unlimited supply of breathing gases, the surface supplied system is the best option. The appropriated mixtures of gases can be sent down by hoses or pipes for short distances and the supply can be monitored from the surface at the support ship or from land. Oxygen supply can be sent down with other gases on a regular bases and keep in compressed bottles to be mix in the habitat as appropriate but a large supply will be needed and also storage capacity within the habitat. In any case, bottles of compressed gases have to be attached to the habitat for emergency situations.
Other important equipments of the breathing systems are the scrubbers that will remove the CO2 produced by the respiration. Helium recovery for deep saturation open habitats will reduce the cost of the operation and some detectors added to the systems will alert on any trace of contaminants within the breathing atmosphere.

Power and Communications [5], [9]
Stand alone batteries technology is not enough to power an underwater habitat for long time, but are essential for emergency situations. Batteries can be charged using cables for electrical transmission and as a primary power system. The source could be a support buoy with solar panels or a generator on the support ship. For higher depth, drag forces on the cable, the weight and currents will make this a very difficult task. Cables laid on the sea floor to power from shore or a close island is another method. Major limitation is that as the distance increases the transformer underwater has to be bigger. New technological developments aim to increase the transmission of DC current over long distances. Nuclear power generation or subsea generators could be considered but the cost is very high and the technology is complex.
Communication underwater is very difficult to achieve by wet links and fiber optics is nowadays the best mechanism for transmission of data. Cables can be connected to a surface buoy with wireless system to the base, a support ship or shore with similar limitations on distance and power. Pingers and emergency communication buoys are added in case of emergency.

Heating and Air Conditioning [10]
Conditioning of the habitat for living includes the control of temperature and humidity levels. As depth increase, temperature will decrease and heat will be transferred from the habitat to the water through the metal surfaces, this transference has to be controlled with isolating materials on the surfaces and heaters. On the other hand compressed air has to be cooled down before being transferred to the compartments to be breathable. Balance of these processes is necessary to maintain an appropriate temperature. The use of helium will increase the loss of heat from the body and heaters are absolutely necessary. In those closed environments, humidity control is important to avoid infections and fungus. Circulation of dry air or gases will need to maintain lower humidity levels.

Viewing [9]
The view of the seafloor site is one of the most attractive things of the underwater habitats. Some habitats are designed with big domes of plexiglass or reinforcement glass panels. From the design point of view making domes and view ports is difficult and as for the structure, reinforcement of the open holes and sealing is very important. Transparent materials have to be selected based on their resistance. At major depth the view ports become smaller. For safety reason the habitats should have a hatch or protective panel that can be closed to avoid damage of the domes or port when the habitat is moved or for emergency in case of failure or crack on the view ports.
Solar light will penetrate the ocean and will be attenuated with depth. Artificial light is necessary to improve visibility and detail viewing of the exterior. Cameras are used to monitor and record the surrounding environment or the exterior of the habitat.

Access and Transportation [5], [10]
Access to shallow water habitats can be done by divers just swimming into the moon pool. For deeper open habitats with mix gas atmospheres, the compression process is a little longer and complex. Compression for commercial saturation diving is done in a chamber on the support ship where after one or two days to avoid physical problems, the divers enter into a close bell which is lower down to the operation depth for the diver to go out and probably transferred to the habitat. Above the diving limits where the inside pressure is maintained at atmospheric pressure, submersibles or bells have to couple in the hatches of the habitat to allow the transference of personnel.


For the assent to surface the aquanauts have to spend some time in a decompression chamber to relive the gases absorbed by the tissues safely. The decompression can be done in one compartment of the habitat or in a chamber on the surface using the same bell as before.
The decompression is a long and delicate process that has to be carefully monitored. In some cases there is no need for decompression, like close habitats at atmospheric pressure with a submersible for transference.

Logistic (Food, water and waste disposal) [5]
Provision of food almost ready to eat will facilitate living, as open flames are not desirables on those close and sensitive environment and space is compromised. Chemical reaction for heating or microwaves could proportionate a safe easy way to heat the meals. Fresh water for personal consumption has to be transported or sent by hoses. Waste water and waste disposal can not be dumped outside. Special collectors, recycling or transported to the surface are some of the methods that can be used.