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=                         Underwater habitat                         =
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                             Introduction
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Underwater habitats 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, recently some new 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 air of suitable quality. Others concern the
physical environment (pressure, temperature, light, humidity), the
chemical environment (drinking water, food, waste products, toxins)
and the biological environment (hazardous sea creatures,
microorganisms, marine fungi). 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.

Numerous underwater habitats have been designed, built and used around
the world since the early 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 and astronaut training,
as well as for research on marine ecosystems.


                        Terminology and scope
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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
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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.


 Architectural variations
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| **Floating**  The habitat is in the underwater hull of a floating
structure. In the 'Sea Orbiter' example this part should reach a depth
of 30 m. The advantage of this type is horizontal mobility.
140px
| **Access shaft to the surface**  The habitat is accessible via a
shaft to above the water surface. The depth of submersion is quite
limited. However, normal atmospheric pressure can be maintained inside
so that visitors do not have to undergo any decompression. This type
is generally used inshore such as the underwater restaurant Ithaa in
the Maldives or Red Sea Star in Eilat, Israel.
140px
| **Semi-autonomous**  Habitats of this type are accessible only by
diving, but energy and breathing gas are supplied by an umbilical
cable. Most stations are of this type, such as 'Aquarius, SEALAB I and
II' and 'Helgoland'
140px
| **Autonomous**  The station has its own reserves of energy and
breathing gas and is able to maneuver itself (at least in the vertical
direction). This type is similar to submarines or atmospheric diving
suits, but it avoids complete environmental separation. Examples of
this type include 'Conshelf III' and 'Bentos-300'.
140px


 Pressure modes
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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, and which 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.

A third or composite type has compartments of both types within the
same habitat structure and connected via airlocks, such as Aquarius.


 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 guidelines 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 to 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 open space available
for exits thus describes 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 13.1 m. Exits were limited vertically to a depth of 6.7 m
(6.4 m above the habitat) and 25.9 m (12.8 m below the habitat level)
and were horizontally limited to a distance of 549 m from the Habitat.


                               History
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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 200 ft.

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 10 m, followed in 1963 by Conshelf II at 11m for a month and
25m 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 63 m2, and was used at a depth of more than 60 m. 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 100 m. 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 186 m. 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.


 Man-in-the-Sea I and II
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The first aquanaut was Robert Stenuit in the Man-in-the-Sea I project
run by Edwin A. Link. On September 6, 1962, he spent 24 hours and 15
minutes at a depth of 61 meters in a steel cylinder, doing several
excursions. In June 1964 Stenuit and Jon Lindbergh spent 49 hours at a
depth of 126 meters in the Man-in-the-Sea II program. The habitat
consisted of a submerged portable inflatable dwelling (SPID).


 Conshelf I, II and III
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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 300 m over the decade; in
reality only three were completed with a maximum depth of 100 m. Much
of the work was funded in part by the French Petrochemical industry,
who, along with Cousteau, hoped that such manned 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 (Continental Shelf Station), constructed in 1962 was the
first inhabited underwater habitat. Developed by Cousteau to record
basic observations of life underwater, Conshelf I was submerged in 10
m 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 10 m 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 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 30 m 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 (World Without Sun)
was awarded an Academy Award for Best Documentary the following year.

Conshelf III was initiated in 1965. Six divers lived in the habitat at
102.4 m 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.


 SEALAB I, II and III
======================
SEALAB was developed by the United States Navy, primarily to research
the physiological aspects of saturation diving.


 Tektite I and II
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Tektite I habitat
The Tektite underwater habitat was constructed by General Electric and
was funded by NASA, the Office of Naval Research and the United States
Department of the Interior.

On February 15, 1969, four Department of the Interior scientists (Ed
Clifton, Conrad Mahnken, Richard Waller and John VanDerwalker)
descended to the ocean floor in Great Lameshur Bay in the United
States Virgin Islands to begin an ambitious diving project dubbed
"Tektite I". By March 18, 1969, the four aquanauts had established a
new world's record for saturated diving by a single team. On April 15,
1969, the aquanaut team returned to the surface after performing 58
days of marine scientific studies. More than 19 hours of decompression
were needed to safely return the team to the surface.

Inspired in part by NASA's budding Skylab program and an interest in
better understanding the effectiveness of scientists working under
extremely isolated living conditions, Tektite was the first saturation
diving project to employ scientists rather than professional divers.

The term tektite generally refers to a class of meteorites formed by
extremely rapid cooling. These include objects of celestial origins
that strike the sea surface and come to rest on the bottom (note
project Tektite's conceptual origins within the U.S space program).

The Tektite II missions were carried out in 1970. Tektite II comprised
ten missions lasting 10 to 20 days with four scientists and an
engineer on each mission. One of these missions included the first
all-female aquanaut team, led by Dr. Sylvia Earle. Other scientists
participating in the all-female mission included Dr. Renate True of
Tulane, as well as Ann Hartline and Alina Szmant, graduate students at
Scripps Institute of Oceanography. The fifth member of the crew was
Margaret Ann Lucas, a Villanova engineering graduate, who served as
Habitat Engineer. The Tektite II missions were the first to undertake
in-depth ecological studies.

Tektite II included 24 hour behavioral and mission observations of
each of the missions by a team of observers from the University of
Texas at Austin. Selected episodic events and discussions were
videotaped using cameras in the public areas of the habitat. Data
about the status, location and activities of each of the 5 members of
each mission was collected via key punch data cards every 6 minutes
during each mission. This information was collated and processed by
BellComm and was used for the support of papers written about the
research concerning the relative predictability of behavior patterns
of mission participants in constrained, dangerous conditions for
extended periods of time, such as those that might be encountered in
manned spaceflight. The Tektite habitat was designed and built by
General Electric Space Division at the Valley Forge Space Technology
Center in King of Prussia, Pennsylvania. The Project Engineer who was
responsible for the design of the habitat was Brooks Tenney, Jr.
Tenney also served as the underwater Habitat Engineer on the
International Mission, the last mission on the Tektite II project. The
Program Manager for the Tektite projects at General Electric was Dr.
Theodore Marton.


 Hydrolab
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Exterior of HydrolabInside Hydrolab
Hydrolab was constructed in 1966 and used as a research station from
1970. The project was in part funded by the National Oceanic and
Atmospheric Administration (NOAA). Hydrolab could house four people.