Air | Water | Nutrition

 
Air  

Astronauts consume a mean value of .98 kg of O₂ per day, producing .8 L of CO₂ for every liter of O₂that they breathe. In previous space missions, the air supply has simply been brought along, the O₂ stored in pressurized tanks and the CO₂ expelled without any form of Oxygen regeneration or carbon dioxide utilization employed. For longer missions, such as an 852 day mission to/on Mars, this method of bringing stored oxygen and expelling the used carbon dioxide is not only impractical, it is implausible. Instead, the air supply must be derived from regenerative methods involving the adsorption, concentration, and conversion of CO₂ to water, which can then undergo electrolysis to form breathable O₂ and H₂ which can be used to replenish fuel cells.

 
 
Liquid Adsorbents

This aspect of the air regeneration system works much like the CO₂ scrubbers used in spacecraft today. The scrubbing system consists of regenerative adsorbents which remove the CO₂ circulating cabin air (Fig.6, 179). For the purposes of this mission, the adsorbents used will be solid amines, which are based on silica gels andsolid amino acid compounds, which may be regenerated by heating to temperatures above 373 K, which does not put stress on the power supply. After the cabin air is circulated through the adsorbent system, scrubbed of CO₂, and returned to the cabin, the CO₂ will be collected with a vacuum, compressed, and collected in a tank, where it will be stored for use in the Sabatier reactor.

 
Sabatier Reactor

The Sabatier reaction, CO₂ + 4H₂ --> CH₄ + 2H₂O , occurs between 523-573K with a nickel catalyst. The production of water and methane is of great use for oxygen regeneration, as the water will be electrolyzed to form oxygen and hydrogen and the methane can either be easily expelled or used for fuel or other ship processes. The Sabatier reaction is thermodynamically stable, and does not require any power to mantain its temperature, making it practical from a power standpoint as well as a chemical one. The only disadvantage to this system is that hydrogen must be continually supplied because of the loss to methane during the reaction. This, too, can be practiccally overcome by using the hydrogen removed from the hydrogen rich water produced by the fuel cells, thus closing the cycle.

 
Air Regeneration Schematic

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Water
 
Each astronaut should consume 2.2-2.5 Liters of water per day. To supply the astronauts with this water, a combination of water synthesis and reclamation will be used.
 
Water Synthesis
Water will be synthesized by fuel cells, which will be powering both the habitat and the craft, each of which will supply 3.78 kg of water per hour. These fuel cells generate hydrogen rich water which must be passed through silver-palladium tubes to create potable water. This hydrogen then goes on to assist in the regeneration of Oxygen in the air loop.

Water Reclamation
Because the chemical composition of human wastes and water contaminants is so complex and varied, the water reclamation system must be able to employ many methods to convert waste water into potable and wash water.
The steps of water reclamation: stabilization of wastes | removal of wastes | mineralization of water | preservation of water  

Stabilization:
Waste Removal:
Mineralization:
Preservation:

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Nutrition
 
Weight of Food | Providing the Food |

Weight of Food

Astronauts need about 1.4 pounds (dry weight) of food per day; this amount may vary depending on the activity level they will be operating at. The breakdown is as follows: 63% of the energy is to be provided by carbohydrates, 25% from fats, and 12% from proteins. The energy provided by each group is, respectively: 4.1, 9.3, and 4.1 kCal per gram. It follows that, when given the number of required KCal (calculated based on the activity levels of the astronauts, the weight per day of food can be calculated using:

w=(.63/4.1)x+(.25/9.3)x+(.12/4.1)x

where w is the weight (in grams) of the food and x is the amount of required calories.

Providing the Food This mission, the food will be provided primarily through freeze dried and rehydratable foods. In other words, we are bringing EVERYTHING with us. Although growing plants in space is plausible, and should be experimented with, that method of feeding astronauts cannot yet be relied upon and should not be fully counted upon, although we should bring along some sort of experiment to test for future missions. Rehydratable food takes up little space, and can be rehydrated using the water generated by fuel cells, which will be powering much of the habitat.

Sample Menu

Some menus from past Russian and US missions:

Typical daily menu of a Soyez cosmonaut Breakfast: Canned meatloaf, bread, chocolate sweets with nut praline, coffee with milk, prune juice Lunch: Canned beef tongue, bread, prunes with nuts Dinner: Caspian roach, bortsch, canned veal, rich pastry, black currant juice Supper: Cream cheese with black currant puree, candied fruit, black currant juice

Now, for contrast... The typical menu of an Apollo astronaut: Breakfast: Apple sauce, sugar frosted flakes, bacon squares, cinnamon toast, cocoa, orange drink Lunch: Beef with vegetables, spaghetti with meat, cheese sandwhich, apricot puding, gingerbread Dinner: Pea soup, tuna salad, cinnamon toast, fruit-cake, pineapple-grapefruit drink.

[Harding, Richard. (1989). Survival in Space. New York: Routledge.]

Metabolic and Nutritional Needs in Space

Metabolic Requirements

Past research has shown that caloric requirements in space do not differ significantly from those on Earth - ranging from 1910 to 3576 kCal/day. There is a shift in the source of caloric energy, however, and this must be accounted for in designing a nutritional plan for long-term space flight. There is an observed loss of lean body mass and weight, and analysis of astronauts' waste shows a negative nitrogen balance. These two factors are evidence that the astronauts source of caloric energy has shifted from food intake to catabolism of tissue protein. This can be counteracted with regular excersize and regulation of diet.

Other effects on diet include:

• a shift in diet from lipids to carbohydrate
• decreased thirst (due to fluid shift)
• decreased appetite (due to gastrointestinal responses to weightlessness)