Apollo 16 Flight Summary	Journal Home Page

The Environmental Control System provides a controlled environment for three astronauts for up to 14 days.  Under normal conditions, this environment includes a pressurized cabin (5 pounds per square inch), a 100- percent oxygen atmosphere, and a cabin temperature of 70 to 75 degrees. For use during critical mission phases and for emergencies, the subsystem provides a pressurized suit circuit. The environmental control unit, a major part of the environmental control subsystem, is produced by Garrett AiResearch, Los Angeles.

The subsystem provides oxygen and hot and cold water, removes carbon dioxide and odors from the CM cabin, provides for venting of waste, and dissipates excessive heat from the cabin and from operating electronic equipment. It is designed so that a minimum amount of crew time is needed for its normal operation.

The environmental control unit is the heart of the environmental control subsystem. It is a compact grouping of equipment about 29 inches long, 16 inches deep, and 33 inches at its widest point. It is mounted in the left-hand equipment bay. The unit contains the coolant control panel, water chiller, two water-glycol evaporators, carbon dioxide-odor absorber canisters, and suit heat exchanger, water separator, and compressors. The oxygen surge tank, water glycol pump package and reservoir, and control panels for oxygen and water are adjacent to the unit.

The subsystem is concerned with three major elements: oxygen, water, and coolant (water-glycol). All three are interrelated and intermingled with other subsystems. These three elements provide the major functions of spacecraft atmosphere and thermal control and water management through four major subsystems: oxygen, pressure suit circuit, water, and water-glycol. A fifth subsystem, post-landing ventilation, also is part of the environmental control subsystem; it provides outside air for breathing and cooling after the command module has splashed down in the ocean.

The oxygen subsystem controls the flow of oxygen within the CM, stores a reserve supply for use during entry and emergencies, regulates the pressure of oxygen supplied to subsystem and pressure suit circuit components, controls cabin pressure, controls pressure in water tanks and the glycol reservoir, and provides for purging the pressure suit circuit.

The pressure suit circuit provides a continuously conditioned atmosphere. It automatically controls suit gas circulation, pressure, and temperature, and removes debris, excess moisture, and carbon dioxide from both suit and cabin gases.

The water subsystem collects and stores potable water, delivers hot and cold water to the crew, and augments the waste water supply for evaporative cooling. The waste water section of the subsystem collects and stores water extracted from the suit heat exchanger and distributes it to the evaporators for cooling.

The water-glycol subsystem provides cooling for the pressure suit circuit, the potable water chiller, and the spacecraft equipment, as well as heating or cooling for the cabin atmosphere.

Last updated: 2017-02-17