Placing a man in space requires a complete life-support system capable
of supplying sufficient oxygen, food, and water and removing excess
carbon dioxide, water vapor, and human body wastes. In addition, the
oxygen, carbon dioxide, and pressure must be maintained at a suitable
level. Any accumulated toxic products and noxious odors must be removed.
In the spacecraft the human is confined in a restricted environment in
which it is necessary to establish a balanced microcosm or closed
ecological system. This is an enormous biological and bioengineering
problem. Weight, size, simplicity of operation, and reliability
particularly are important factors.
For relatively short missions involving one or several astronauts, food,
oxygen, and water can be stored and made available as required, and the
various waste products can be stored. On longer missions, particularly
those involving more than one astronaut, efficient chemical or
biological regenerative systems will be required. Any regenerative
system introduces a fixed cost in weight of processing equipment and
energy requirements.
Chemical, or partially regenerative, methods for providing breathing
oxygen by the regeneration of metabolic products such as water vapor and
carbon dioxide include the thermal decomposition of water and CO₂,
photolysis and radiolysis of water, electrolysis of fused carbonates and
aqueous solutions, and the chemical reduction of CO₂ with H₂, followed
by electrolysis of the water formed. Chemical regenerative systems have
been developed to remove excess carbon dioxide and water vapor from the
atmosphere. Nonbiological regenerative systems are time limited by the
amount of food, water, and oxygen that can be carried or recovered.
These physical-chemical processes show great potential, but they also
present many difficulties, including requirements for extremely high
temperatures and considerable amounts of power, the formation of highly
toxic materials, and high susceptibility to inactivation. None of the
presently studied nonbiological processes can function as completely as
a bioregenerative system. All these nonbiological systems have
unrealistic supply requirements and produce unusable wastes.
Consequently, for long planetary missions the bioregenerative systems,
though also beset with problems, are potentially far superior to their
physical and chemical counterparts.
Table VIII shows average daily metabolic data for a 70-kg astronaut. A
man breathes about 10 cubic feet of air per minute, or 400 000 liters,
daily. The expired air contains about 4 percent carbon dioxide. Man
normally breathes air containing 0.03 percent CO₂, but can withstand
comfortably about 1.5 percent CO₂. Anything in excess of 1.5 percent
will produce labored breathing, headaches, and, if greatly exceeded,
death. A man exhales about 1.1 pounds of water per day and this, in
addition to water from perspiration and other sources, must be removed
from the air.
Table VIII.—_Average Daily Metabolic Data for a 70-kg,
25-Year-Old Astronaut With Normal Spacecrew Activity_
[From [ref.173]]
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O₂ input, kg 0.862
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CO₂ output, kg 1.056
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Drinking water, liters 2.5
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Food rehydrating water, liters 1
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Caloric value of food, kcal 3000
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Water output:
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Urine, liters 1.6
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Respiration and perspiration, liters 2.13
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Feces, kg 0.09
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Total heat output, Btu 11 100
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Two types of biological regenerative systems have been proposed. The
photosynthetic closed ecological system was proposed as early as 1951.
This involves the use of single-celled algae or higher plants, including
floating aquatic and terrestrial plants, and requires the interaction of
light energy with CO₂ and H₂O to produce O₂ and plant cells. Another
system, proposed in 1961, involves electrolysis of water into oxygen and
hydrogen, and the concurrent use of _Hydrogenomonas_ bacteria which take
up hydrogen, some oxygen, carbon dioxide, and urine yielding water and
bacterial cells.
Table IX.—_Requirements for Regenerative Life-Support Systems_
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Requirements / Requirements /
1 man⁴ 3 men (270 man-day
System mission)⁵
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Weight, Power, Weight, Power,
kg kW kg kW
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Partial chemoregenerative ⁷ 332 1.75
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LiOH 125 1.40
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NaOH 155 7.68
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CO₂-H₂ 34 .36
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Full bioregenerative—algae:
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Artificial illumination 116 ⁶ 10.40 591 25.00
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Solar illumination 103 1.70 356 .60
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Electrolysis-_hydrogenomonas_ 55 .25 129 2.60
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⁴ From [ref.174].
⁵ From [ref.175].
⁶ From [ref.176].
⁷ Includes instrumentation and food storage.
The values given in table IX indicate relative weights and powers
required by various systems to provide the gaseous environment for
manned space cabins. If one considers operating temperatures and
hazards, other systems may offer advantages which offset the weight and
power advantages of the hydrogen reduction of LiOH systems.
Research is being conducted by NASA on life-support-system technology
applicable to missions planned for 20 years in the future. Life-support
systems include the requirements for supplying breathing gases, control
of contaminants in the cabin atmosphere, water reclamation, food supply,
and personal hygiene. The disciplines involved in such systems include
biology and microbiology, cryogenic fluid handling at zero g, heat
transfer, and thermal integration with other systems, such as power. The
physiological, psychological, and sociological problems of the crew are
also being considered.