Deployed 19 metres underwater, 5.6 km off Key Largo, in the Florida Keys National Marine Sanctuary, Aquarius is an undersea laboratory designed to support research in coastal and ocean resource science and management. The habitat itself, a steel cylinder 3 metres in diameter by 14 metres long, provides 11 cubic metres of living and laboratory space for a six-person crew. The lab is equipped with computers networked to shore, Internet, telephones, radios, and videoconferencing equipment.
Aquarius is an ambient pressure habitat – this means its interior atmospheric pressure is equal to the surrounding water pressure. At this depth and pressure, visitors diving down to Aquarius have only about 80 minutes to complete their stay and return to the surface before they risk experiencing decompression-related illness. However, the mission crew, known as "aquanauts," can stay indefinitely. They also have nearly unlimited bottom time during their scuba dives out of the habitat, as long as they stay at the same depth. However, the cost of long stays at this pressure is that at the end of a mission, aquanauts must undergo a 17-hour decompression in a chamber within Aquarius itself in order to minimize the risk of decompression sickness. At the end of decompression, aquanauts exit the habitat and scuba dive back to the surface.
Aquarius missions usually last about ten days and are conducted from April through November. This extreme, hostile environment is analogous to conditions for human space flight and has been used by NASA in the training of space station astronauts and as a platform for research and technology development since 2001.