Manned Space Flight
BIOREGENERATIVE LIFE-SUPPORT SYSTEMS
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.
O2 input, kg | 0.862 |
CO2 output, kg | 1.056 |
Drinking water, liters | 2.5 |
Food rehydrating water, liters | 1 |
Caloric value of food, kcal | 3000 |
Water output: | |
Urine, liters | 1.6 |
Respiration andperspiration, liters | 2.13 |
Feces, kg | 0.09 |
Total heal output, Btu | 11 100 |
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.
System | Requirements/1 man[4] | Requirements/3 men(270 man-daymission)[5] | ||
|---|---|---|---|---|
Weight,kg | Power,kW | Weight,kg | Power,kW | |
Partial chemoregenerative | [7] 332 | 1.75 | ||
LiOH | 125 | 1.40 | ||
NaOH | 155 | 7.68 | ||
CO2-H2 | 34 | .36 | ||
Full bioregenerative—algae: | ||||
Artificial illumination | 116 | [6] 10.40 | 591 | 25.00 |
Solar illumination | 103 | 1.70 | 356 | .60 |
Electrolysis-hydrogenomonas | 55 | .25 | 129 | 2.60 |