OVERVIEW:

Biosphere 2 represents an engineering achievement of enormous complexity. During the first two-year mission, its huge physical plant operated successfully, sustaining eight humans and approximately 3,800 species of plants and animals in seven biomes with no major operational setbacks. In the process, it demonstrated that it is indeed possible to create a closed ecological system that can support human beings.

THE PHYSICAL PLANT:

Biosphere 2 is a huge greenhouse that covers approximately 3.15 acres and measures seven million cubic feet in volume. At its highest point, it is 85 feet high.

Biosphere 2's physical plant includes the Technosphere - the "basement" that underlines the structure and contains the vast mechanical and electronic machinery that keeps Biosphere 2 operating.

MECHANICAL SYSTEMS:

Biosphere 2's mechanical systems operate around the clock to circulate air and water and control temperature.

Its 25 air handlers can circulate air up to 600 cubic meters a second throughout the structure.

Biosphere 2 contains complex, miniature ecosystems, such as a tropical rainforest and an ocean biome. Innovative mechanical systems were designed to generate tides, currents, waves and rain, as well as to control salinity gradients and aid nutrient cycling.

The vast machinery housed within Biosphere 2 includes more than 200 electronic motors and 120 pumps - all overseen by the crew's master technician, Co-Capitan Mark Van Thillo.

There were no major mechanical problems. All kinds of things didn't go wrong: there were no major energy failures; no contamination of fresh water storage systems; no serious corrosion; no electrical problems, despite humidity and the ocean biome's salty environment.

THE SEAL:

In its two years of operation, Biosphere 2 has proven to be the world's most tightly sealed structure of its kind.

Biosphere 2's leak rate is under ten percent a year (confirmed by independent scientists). The closed- system facility built by NASA at Kennedy Space Center leaks ten percent a day. The leak rate of NASA's space shuttle is 350 percent a year.

A leak detection system was built into Biosphere 2 underneath its liner. In one test, sulfur hexaflouride gas was released into the air; its concentration was monitored over time to measure its dilution by air entering Biosphere 2 from the outside. The leak rate was determined to be six percent a year.

To achieve this tight seal, Biosphere 2's designers created a unique system of glass and steel construction. Each of the 8,000 glass panes is actually two layers of heat-strengthened glass joined by a plastic laminate. The Biosphere's steel struts are covered with a state-of-the-art finish to protect them from corrosion. Below ground, the Biosphere's concrete foundation is lined with a high-grade stainless steel which forms a continuous welded pan.

The structure's effective seal has allowed scientists to study oxygen, carbon dioxide, and trace gas dynamics inside Biosphere 2. Oxygen depletion within the Biosphere would not have been detected in a less airtight structure. This unexpected phenomenon has excited scientists, who hope to gain insight into a similar but much slower oxygen depletion in Earth's atmosphere.

THE ENERGY SYSTEM:

Biosphere 2's elaborate mechanical and electronic systems are powered by external co-generating electrical generators housed in an Energy Center adjacent to the Biosphere structure.

The Energy Center is a "total energy system," using state-of-the-art technology to provide energy with maximum efficiency. Pumps are selected to operate at about 80 percent efficiency. The air conditioning fans are equipped with variable air flow control to exactly match the demand and thereby conserve energy. High-efficiency sodium lights are used for illumination in the Biosphere and the Energy Center.

The energy system was designed to be environmentally sound. The fuel used at the Energy Center is clean-burning natural gas. The system avoids the polluting water discharges common to many power plants by using advanced water treatment methods. The cooling system minimizes the use of refrigerants, and uses only those refrigerants that do no harm to the ozone layer.

The energy system is designed for conversion to solar energy as soon as that becomes economically feasible.

Climate control is the single greatest challenge to the energy system, since Biosphere 2 must maintain tropical ecosystems in the Arizona desert. Temperature control is achieved by means of water - heated, chilled, or evaporatively cooled_which runs through 1.5 miles of closed-loop piping inside the Biosphere.

Biosphere 2 uses an efficient water cooling system designed to make maximum use of natural cooling. This system is designed around the evaporation of water in three cooling towers located outside Biosphere 2. This method is more environmentally sound (and 20 times less costly) than cooling by conventional refrigeration compressors.

The energy system recaptures the heat emitted by the engines that run Biosphere's generators. These heat wastes are used in an "absorption chiller" to produce chilled water for cooling the Biosphere. Jacket water heat is transferred into hot water and used to heat the Biosphere.

"The challenge has been to determine what's required to create an indefinitely self- sustaining, regenerating life-support system. It's difficult to convey the complexity of that undertaking - how much detail has to be covered in order to make something like this operate at all."

Bill Dempster, Director of Systems Engineering

"If you haven't seen Biosphere 2, it's hard to imagine how vast and extensive the technical systems are that were put in here to create waves and tides, to create rainfall and breezes, to humidify the rain forest and dehumidify our desert, to keep a river running, to clean up waste water, and on and on."

Biospherian Mark Nelson