Underwater habitat
Underwater habitats are a form of subsea technology. They are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene and sleeping. In this context, 'habitat' is generally used in a narrow sense to mean the interior and immediate exterior of the structure and its fixtures, but not its surrounding marine environment. Most early underwater habitats lacked regenerative systems for air, water, food, electricity, and other resources. However, some underwater habitats allow for these resources to be delivered using pipes, or generated within the habitat, rather than manually delivered.
An underwater habitat has to meet the needs of human physiology and provide suitable environmental conditions, and the one which is most critical is breathing gas of suitable quality. Others concern the physical environment, the chemical environment and the biological environment. Much of the science covering underwater habitats and their technology designed to meet human requirements is shared with diving, diving bells, submersible vehicles and submarines, and spacecraft. It incorporates various developments used in other forms of subsea technology.
Numerous underwater habitats have been designed, built and used around the world since as early as the start of the 1960s, either by private individuals or by government agencies. They have been used almost exclusively for research and exploration, but in recent years, at least one underwater habitat has been provided for recreation and tourism. Research has been devoted particularly to the physiological processes and limits of breathing gases under pressure, for aquanaut, as well as astronaut training and for research on marine ecosystems.
Terminology and scope
The term 'underwater habitat' is used for a range of applications, including some structures that are not exclusively underwater while operational, but all include a significant underwater component. There may be some overlap between underwater habitats and submersible vessels, and between structures which are completely submerged and those which have some part extending above the surface when in operation.In 1970 G. Haux stated:
At this point it must also be said that it is not easy to sharply define the term "underwater laboratory". One may argue whether Link's diving chamber which was used in the "Man-in-Sea I" project, may be called an underwater laboratory. But the Bentos 300, planned by the Soviets, is not so easy to classify as it has a certain ability to maneuver. Therefore, the possibility exists that this diving hull is classified elsewhere as a submersible. Well, a certain generosity can not hurt.
Comparison with surface based diving operations
In an underwater habitat, observations can be carried out at any hour to study the behavior of both diurnal and nocturnal organisms. Habitats in shallow water can be used to accommodate divers from greater depths for a major portion of the decompression required. This principle was used in the project Conshelf II. Saturation dives provide the opportunity to dive with shorter intervals than possible from the surface, and risks associated with diving and ship operations at night can be minimized. In the habitat La Chalupa, 35% of all dives took place at night. To perform the same amount of useful work diving from the surface instead of from La Chalupa, an estimated eight hours of decompression time would have been necessary every day.However, maintaining an underwater habitat is much more expensive and logistically difficult than diving from the surface. It also restricts the diving to a much more limited '''area.'''
Technical classification and description
Architectural variations
Pressure modes
Underwater habitats are designed to operate in two fundamental modes.- Open to ambient pressure via a moon pool, meaning the air pressure inside the habitat equals underwater pressure at the same level, such as SEALAB. This makes entry and exit easy as there is no physical barrier other than the moon pool water surface. Living in ambient pressure habitats is a form of saturation diving, and return to the surface will require appropriate decompression.
- Closed to the sea by hatches, with internal air pressure less than ambient pressure and at or closer to atmospheric pressure; entry or exit to the sea requires passing through hatches and an airlock. Decompression may be necessary when entering the habitat after a dive. This would be done in the airlock.
Components
Excursions
An excursion is a visit to the environment outside the habitat. Diving excursions can be done on scuba or umbilical supply, and are limited upwards by decompression obligations while on the excursion, and downwards by decompression obligations while returning from the excursion.Open circuit or rebreather scuba have the advantage of mobility, but it is critical to the safety of a saturation diver to be able to get back to the habitat, as surfacing directly from saturation is likely to cause severe and probably fatal decompression sickness. For this reason, in most of the programs, signs and guide lines are installed around the habitat in order to prevent divers from getting lost.
Umbilicals or airline hoses are safer, as the breathing gas supply is unlimited, and the hose is a guideline back to the habitat, but they restrict freedom of movement and can become tangled.
The horizontal extent of excursions is limited by the scuba air supply or the length of the umbilical. The distance above and below the level of the habitat are also limited and depend on the depth of the habitat and the associated saturation of the divers. The volume of the underwater environment available for excursions thus takes the shape of a vertical axis cylinder centred on the habitat.
As an example, in the Tektite I program, the habitat was located at a depth of. Excursions were limited vertically to a depth of and and were horizontally limited to a distance of from the Habitat.
History
The history of underwater habitats follows on from the previous development of diving bells and caissons, and as long exposure to a hyperbaric environment results in saturation of the body tissues with the ambient inert gases, it is also closely connected to the history of saturation diving. The original inspiration for the development of underwater habitats was the work of George F. Bond, who investigated the physiological and medical effects of hyperbaric saturation in the Genesis project between 1957 and 1963.Edwin Albert Link started the Man-in-the-Sea project in 1962, which exposed divers to hyperbaric conditions underwater in a diving chamber, culminating in the first aquanaut, Robert Sténuit, spending over 24 hours at a depth of.
Also inspired by Genesis, Jacques-Yves Cousteau conducted the first Conshelf project in France in 1962 where two divers spent a week at a depth of, followed in 1963 by Conshelf II at for a month and for two weeks.
In June 1964, Robert Sténuit and Jon Lindberg spent 49 hours at 126m in Link's Man-in-the-Sea II project. The habitat was an inflatable structure called SPID.
This was followed by a series of underwater habitats where people stayed for several weeks at great depths. Sealab II had a usable area of, and was used at a depth of more than. Several countries built their own habitats at much the same time and mostly began experimenting in shallow waters. In Conshelf III six aquanauts lived for several weeks at a depth of. In Germany, the Helgoland UWL was the first habitat to be used in cold water, the Tektite stations were more spacious and technically more advanced. The most ambitious project was Sealab III, a rebuild of Sealab II, which was to be operated at. When one of the divers died in the preparatory phase due to human error, all similar projects of the United States Navy were terminated. Internationally, except for the La Chalupa Research Laboratory the large-scale projects were carried out, but not extended, so that the subsequent habitats were smaller and designed for shallower depths. The race for greater depths, longer missions and technical advances seemed to have come to an end.
For reasons such as lack of mobility, lack of self-sufficiency, shifting focus to space travel and transition to surface-based saturation systems, the interest in underwater habitats decreased, resulting in a noticeable decrease in major projects after 1970. In the mid eighties, the Aquarius habitat was built in the style of Sealab and Helgoland and is still in operation today.
Historical underwater habitats
Man-in-the-Sea I and II
The first aquanaut was Robert Stenuit in the Man-in-the-Sea I project run by Edwin A. Link. On 6 September 1962, he spent 24 hours and 15 minutes at a depth of in a steel cylinder, doing several excursions. In June 1964 Stenuit and Jon Lindbergh spent 49 hours at a depth of in the Man-in-the-Sea II program. The habitat consisted of a submerged portable inflatable dwelling.Conshelf I, II and III
Conshelf, short for Continental Shelf Station, was a series of undersea living and research stations undertaken by Jacques Cousteau's team in the 1960s. The original design was for five of these stations to be submerged to a maximum depth of over the decade; in reality only three were completed with a maximum depth of. Much of the work was funded in part by the French petrochemical industry, who, along with Cousteau, hoped that such colonies could serve as base stations for the future exploitation of the sea. Such colonies did not find a productive future, however, as Cousteau later repudiated his support for such exploitation of the sea and put his efforts toward conservation. It was also found in later years that industrial tasks underwater could be more efficiently performed by undersea robot devices and men operating from the surface or from smaller lowered structures, made possible by a more advanced understanding of diving physiology. Still, these three undersea living experiments did much to advance man's knowledge of undersea technology and physiology, and were valuable as "proof of concept" constructs. They also did much to publicize oceanographic research and, ironically, usher in an age of ocean conservation through building public awareness. Along with Sealab and others, it spawned a generation of smaller, less ambitious yet longer-term undersea habitats primarily for marine research purposes.Conshelf I, constructed in 1962, was the first inhabited underwater habitat. Developed by Cousteau to record basic observations of life underwater, Conshelf I was submerged in of water near Marseille, and the first experiment involved a team of two spending seven days in the habitat. The two oceanauts, Albert Falco and Claude Wesly, were expected to spend at least five hours a day outside the station, and were subject to daily medical exams.
Conshelf Two, the first ambitious attempt for men to live and work on the sea floor, was launched in 1963. In it, a half-dozen oceanauts lived down in the Red Sea off Sudan in a starfish-shaped house for 30 days. The undersea living experiment also had two other structures, one a submarine hangar that housed a small, two-man submarine named SP-350 Denise, often referred to as the "diving saucer" for its resemblance to a science fiction flying saucer, and a smaller "deep cabin" where two oceanauts lived at a depth of for a week. They were among the first to breathe heliox, a mixture of helium and oxygen, avoiding the normal nitrogen/oxygen mixture, which, when breathed under pressure, can cause narcosis. The deep cabin was also an early effort in saturation diving, in which the aquanauts' body tissues were allowed to become totally saturated by the helium in the breathing mixture, a result of breathing the gases under pressure. The necessary decompression from saturation was accelerated by using oxygen enriched breathing gases. They suffered no apparent ill effects.
The undersea colony was supported with air, water, food, power, all essentials of life, from a large support team above. Men on the bottom performed a number of experiments intended to determine the practicality of working on the sea floor and were subjected to continual medical examinations. Conshelf II was a defining effort in the study of diving physiology and technology, and captured wide public appeal due to its dramatic "Jules Verne" look and feel. A Cousteau-produced feature film about the effort was awarded an Academy Award for Best Documentary the following year.
Conshelf III was initiated in 1965. Six divers lived in the habitat at in the Mediterranean Sea near the Cap Ferrat lighthouse, between Nice and Monaco, for three weeks. In this effort, Cousteau was determined to make the station more self-sufficient, severing most ties with the surface. A mock oil rig was set up underwater, and divers successfully performed several industrial tasks.