International Space Station

Environmental Control and Life Support System

Environmental Control and Life Support SystemLife goes on in the International Space Station because the systems that sustain it have been thought out and designed with as much thoroughness and precision as can be brought to any human endeavor.

The ISS Environmental Control and Life Support System provides or controls fundamental facts of life that most Americans take for granted: oxygen and other gases, the atmospheric pressure required to breathe, water, fire fighting and the like.

Priority One for the system is the ISS atmosphere. But the system also collects, processes and stores water and waste used and produced by the crew. The System will recycle, for example, fluid from the sink, shower, urine, the Space Shuttle's fuel cells, and condensation -- an on-orbit first.

Control of the environment and provision of life support is organized into five subsystems:

Atmosphere Control and Supply provides oxygen and nitrogen, gases used in experiments and for other purposes, and atmospheric pressure. It also maintains oxygen and nitrogen levels, as well as pressure, in the proportions found at sea level: about 21% oxygen, 78% nitrogen at 14 lbs. per square inch.

The Russian segment of the ISS has primary responsibility for these functions during the early assembly. Oxygen will be supplied primarily by the Elektron electrolysis system, which separates water molecules into hydrogen and oxygen. The U.S. will begin providing additional oxygen, nitrogen and pressurization services from refillable tanks at the end of Assembly Phase I via pipes running throughout the U.S. segment.

The Atmosphere Revitalization Subsystem removes carbon dioxide and most trace contaminants while monitoring oxygen and nitrogen levels. Special absorbent materials are used to collect carbon dioxide, which is expelled into space.

Temperature and Humidity Control circulates air, removes humidity and maintains the ISS atmosphere within a constant temperature range. The workhorse of the Subsystem is the Common Cabin Air Assembly, which pulls air through filters, cools and dehumidifies it, and diffuses it back into the atmosphere. The water removed is sent to the Water and Recovery Management Subsystem.

As noted above, the Water Recovery and Management Subsystem will recover and recycle water from the sink, shower, urine, the Space Shuttle's fuel cells, and condensation. A Potable Water Processor refines waste water into drinkable water. Water quality is monitored by a Process Control and Water Quality Monitor.

The Fire Detection and Suppression Subsystem cconsists of smoke detectors, alarms and shutoff systems, portable fire extinguishers, gas masks and oxygen bottles. Two area smoke detectors are provided in each pressurized module, and one is installed in each rack requiring an Avionics Air Assembly (circulation and ventilation equipment).