Jim_Day.XSIS@xerox.com (12/07/90)
Someday, perhaps within the next century, the necessities of life may be supplied by nanodevices (NADs). What would such devices do? That depends on how the necessities of life are defined. In the most fundamental sense, the necessities of life are such things as oxygen, food, water, and a habitat with a tolerable range of air temperature, pressure, and humidity. To focus more sharply on the basic parameters of life support, it might be useful to consider a habitat isolated from ordinary terrestrial conditions. Such a habitat is discussed in some detail in NASA report SP-413, Space Settlements: A Design Study. The report is based on a study done in 1975 at Stanford and NASA's Ames Research Center. Among the 31 participants were Thomas Heppenheimer, Gerard O'Neil, and Eric Drexler. The technical information that follows reflects the results of that study. People living and working in space need about 3000 calories per day. Their daily diet would include 2 kg of water, 470 kg of fats and carbohydrates, 60 to 70 g of proteins, and essential vitamins and minerals. The NASA report mentions the possibility of synthesizing food but adds that this is "not yet economically feasible." The report makes no mention of nanotechnology, but it seems reasonable to assume that, with the aid of nanotechnology, food synthesis might become cheaper than producing food by agricultural methods. In a self-sufficient space habitat, all biological waste must be recycled. The report discusses several recycling methods and suggests use of the Zimmerman wet oxidation process. The Zimmerman process operates at a temperature of 260 degrees Celsius and a pressure of 1500 pounds per square inch, with a cycle time of 90 minutes. The report assumes a per capita power use of 3 kW, which is about twice the current U.S. per capita consumption. The additional power would be needed to recycle wastes. Electrical power would be derived from sunlight, either by photovoltaic or thermal conversion. Water would be recycled in two ways. Drinking water would be obtained by condensation from the air of the habitat. Water would also be obtained as a byproduct of the Zimmerman process used to recycle biological waste. This water, containing small amounts of phosphate ash and ammonia, would be used for purposes other than drinking or cooking. The atmosphere of the habitat described in the report would have a temperature of about 20 degrees Celsius and a relative humidity of 50 percent. The air pressure would be half that at sea level on Earth, with a nitrogen pressure of 200 mmHg and an oxygen pressure of 170 mmHg. Pressure contributed by water vapor would be about 7.5 mmHg, and carbon dioxide pressure would be less than 3 mmHg. The report suggests the use of photosynthesis to maintain the desired levels of oxygen and carbon dioxide. If NADs were used to synthesize food, then it would be reasonable to use them to control the balance of carbon dioxide and oxygen also. It seems likely that food synthesis, the recycling of biological waste, and maintenance of a healthy atmosphere would be closely interrelated processes in a space habitat (as they are on Earth).