Electrolysis is carried out in a closed unit containing an electrolyte
(KOH solution) with an anode and a cathode. These cells produce a
maximum yield (60-80 percent or more) in gas production per unit of
power consumption. According to Dole and Tamplin ([ref.184]), a unit
capable of producing enough oxygen to sustain one man would be highly
reliable, weigh approximately 18 kg, and require a power input of 0.25
kW.
One approach to zero-gravity operation is to rotate the electrolysis
cell as described by Clifford and McCallum ([ref.185]) and Clifford and
Faust ([ref.186]). The smallest known electrolysis cell under
development uses this artificial gravity to separate oxygen from the
anode and electrolyte, while the dry hydrogen gas permeates through the
foil cathode, fabricated from palladium-silver alloy. This electrolysis
cell, which would provide breathing oxygen for three men, has a volume
of 1.4 liters, weighs 4.5 kg, and requires 0.67 kW, excluding auxiliary
equipment, and has an efficiency of 84 percent.
The chemosynthetic conversion is carried out by the hydrogen bacteria.
By the oxidation of molecular hydrogen, supplied from the electrolysis
of water, energy is made available for biosynthesis. The generation of
this "biological energy" is mediated by the stable enzyme hydrogenase
which is present in the bacteria. On the average, the oxidation of 4
moles of H₂ is required for the conversion of 1 mole of CO₂ (the hourly
production of a man). The removal of this amount of CO₂ would thus
require the cleavage of 4 moles of water. In addition, to supply oxygen
for human respiration (at a rate of 1 mole of O₂ per hour) the cleavage
of two additional moles of water is required. Therefore, the
chemosynthetic regeneration and human respiration together would
require, on the average, the splitting of 6 moles of water per hour.
The material balance for electrolysis, biosynthesis, and human
metabolism, with gram molecular weights in parentheses, are shown in
equations (1) to (3), respectively:
6H₂O ———————> 3O₂ + 6H₂
(108) ———————> (96) + (12) (1)
The bacterial synthesis requires 6 moles of H₂, 2 moles of O₂, and 1
mole of CO₂ (from the astronaut), as shown in equation 2:
6H₂ + 2O₂ + CO₂ ———————> CH₂O + 5H₂O
(12) + (64) + (44) ———————> (30) + (90) (2)
The respiration of the astronaut requires 1 "food" mole (CH₂O)
representing about 120 kcal, and 1 mole of O₂, as shown in equation 3:
CH₂O + O₂ ———————> CO₂ + H₂O
(30) + (32) ———————> (44) + (18) (3)
The metabolic data in table VIII show that the CO₂ of the astronaut and
the bacteria must balance at about 1.056 kg per day.
The water relations are not completely balanced, but are fairly close.
About 2.6 liters per day of water are split by electrolysis. The
astronaut has an intake of 3.5 liters of water per day, 2.5 liters for
drinking and 1 liter for preparing dehydrated food. The output is about
1.6 liters of urine and 2.1 liters of water of respiration and
perspiration per day, or a total output of 3.7 liters, with the
0.2-liter excess due mainly to water of metabolism. The
bacteria-produced water, amounting to 2.2 liters per day, and the excess
from the astronaut would supply 2.4 liters toward balancing the 2.6
liters of water electrolyzed.