In the original TMP Marshal Savage proposed the use of submarine habitats as a training ground for prospective space residents who would use life in such habitats as a means of growing familiar with living in confined spacecraft-like spaces and coping with the demands of maintaining an artificial life support system. NASA and other government space agencies have employed submarine habitats with similar objectives. There is no question that the marine environment offers a closest analogy to the microgravity environment and that underwater facilities will be a practical tool in space development. But the need for large communities underwater is unlikely. However, this will not deter the demand for underwater habitat structures of some kind for Aquarius, even if their function is less practical and more aesthetic and recreational. Indeed, there is already a slow but steady growth in the development of such structures for use as hotels, restaurants, and theme park and aquarium features in the usual tropical tourist zones of the world.
Submarine colonies -often depicted as fanciful transparent domed cities- have long been a common feature of SciFi and futurist visions. But in most cases the proponents of such communities overlook the simple fact that, even with the clearest water, below a depth of about 100 feet light transmission from the surface drops off dramatically and there is simply nothing outside to see without the constant aid of artificial lighting. While sea floor colonies may become a reality in the future, they will likely be little different from the subterranean colonies employed on other planets, their structures excavated or formed by thick concrete bunkers.
But near the surface -above that 100 foot depth- the marine environment can be quite light, lively, and engaging. This is the environment everyone imagines when they think of life under the sea. The zone of most visible life and the area immediately accessible to the free-swimming and scuba-diving human being. And it is in this zone that we are already seeing a steady exploration in novel submarine architecture. The most promising area for this today is structures based on the use of transparent Lexan shell systems, commonly employed in simple cylindrical shapes but increasingly capable of an infinite variety of forms which can be outfit for habitation by light retrofit interior structures and enhanced functionally and aesthetically by novel optical systems and laminate electrical and electronic systems. Whether functional or not, there will always be a cultural demand for convenient and intimate access to the marine environment among marine settlement residents with submarine structures being as logical and obvious an expression of that as recreational lagoons and artificial beaches. Indeed, despite the fact that they may never be truly 'cost effective' in a conventional sense, it is quite likely for these structures to be experimented with even in the earliest stages of Aquarius Seed settlements, especially considering their profit potential as tourist attractions. Thus with TMP 2 we anticipate the likely development of large, sophisticated, and often fanciful shallow water submarine architecture as a feature of many marine colonies.
These shallow water submarine habitats will likely be partly integrated into the general structure of the colony -especially in the case of those employing free-form organic design- and extend outward as branching submerged complexes divided by watertight compartment doors where most spaces have at least two exits. They will be relegated mostly to sheltered water areas dedicated to their use or multiple recreational uses, in order that they be safe environments for free-swimming around them. They would be ambient pressure structures, since they have no need of deep water location and the complications of pressurized structures would only make them less convenient for casual habitation.
The basic form of submarine structure would be a thick walled cast lexan shell in tubular, spherical, and flowing organic shapes which are precast in large pieces that are then fused together to form a visually seamless shell at the surface of a construction site before being lowered into the water. Some structure may be assembled as a series of precast room modules joined in water along connecting tubes using demountable water-tight hatches and special coffer dam enclosures. While generally strong, this material suffers loss of integrity where penetrated by other materials and so structures would tend to follow the patterns of free-form ferro-cement interior shell designs with surface-mounted external components while interior fixtures would consist of internally retrofit modular component decking and mezzanine systems customized to suit the flowing organic shell shapes. In effect, these structures would be bubbles with largely independent habitable structures suspended within them and with some use of external space frames -possible disguised as coral and natural marine concretion structures- to help rigidize and support them.
There may also be some experimentation with the use of submarine 'tents' created by enclosing a space frame compression structure with a thin but tough tensioned transparent elastomeric membrane material such as Texlon and later some forms of nanfabricated diamondoid membranes. These would be more transparent than glass or lexan and much cheaper but would demand considerable ballast. This form of structure, based on other even tougher opaque membrane materials, may become quite useful for more industrial and research applications thanks to its economy and potential to support large areas, even though it would not be suited to deep sea pressures. Such submarine tents may offer a fair analogy to the TransHab style of space habitat and so could serve the role of experimental habitats in large neutral buoyancy test facilities.
This sprawling underwater habitat would tend toward primarily recreational use. Though it may employ hotel spaces, it would generally be too costly for general housing uses and, to maximize the benefit of the construction for all, would favor applications suited to public community activity such as public lounges and spas, walk-through reef gardens, marine playgrounds, restaurants, dance halls, and the like.