Of all the essentials of life, oxygen (
O2) is the most important. Korean Haenyeo divers can hold their breath for over three minutes. But for the rest of us, hypoxia, the sudden loss of O2, results in unconsciousness within seconds.
Carbon dioxide (CO2) in elevated concentrations is toxic. Ten percent renders us unconscious. Nitrogen (N2), the majority atmospheric constituent, is critical for long-term sustainment of life. Water, in the form of rain and snow is vital on Earth, but in a confined space containing electronics it can pose serious risks.
The regulation of these gases on board spacecraft and future bases on the Moon and Mars is accomplished by a chain of chemical reactions. For our discussion, let’s begin with the respiration of a glucose molecule by a crew member.
When metabolized, this six-carbon sugar provides the energy that makes life possible. Our crew member exhales the byproducts, CO2 and water. In the closed quarters of the International Space Station (
ISS), accumulating CO2 quickly becomes life-threatening. Exhaled water condenses in electronics, increasing the risks of short circuits and/or fire.
Glucose and oxygen metabolism is represented with the following chemical equation:
C6H12
O6 + 6
O2 → 6
CO2 + 6
H2O
When it was first deployed, the ISS employed a CO2 scrubber. Lithium hydroxide absorbed the gas and then vented it into space. Water vapor was collected and added to the water recycling system.
The O2 used up in respiration was replenished through water electrolysis. The hydrogen (
H2)generated was also vented. See the
October 2022 issue of JOTH for an examination of electrolysis tech. Because only half the water required to maintain O2 levels was recycled, regular supplemental shipments were flown to the ISS.
Here is the chemical reaction of electrolysis:
6
H2
O(
recycled) + 6
H2
O(
supplemental) → 6
O2 + 12
H2
In 2010 this wasteful environmental system was partially addressed with the Advanced Closed Loop System (
ACLS). By adding a Sabatier reactor, the ACLS combined the CO2 from respiration with the H2 left over from electrolysis, yielding water and methane (
CH4).
Today, the water added by the Sabatier reactor is returned to the electrolysis process. Only the methane is vented into space. However, each molecule vented represents the net loss of two H2 molecules. H2 is routinely shipped to the ISS to make up for what is wasted.
Here is the Sabatier chemical equation:
6
CO2 + 12
H2(from electrolysis) + 12
H2(supplemental) → 12
H2O + 6
CH4
This system works well for orbital facilities that can be readily resupplied with H2. That might even include future long-term lunar missions, where resupply from Earth is a three-day flight away.
But for flights to Mars, and Red Planet surface bases, NASA is evaluating adding methane pyrolysis to completely close the loop. Heating CH4 to 1200 degrees Celsius in a steel reactor vessel dissociates it into its constituent elements, atomic carbon and H2.
The solid carbon can be removed from the chamber and used to create organic compounds, or for graphene, the precursor of carbon fiber. The H2 can be returned to the Sabatier process, eliminating shipments of supplemental H2. Look for a pyrolytic system to be tested on the Lunar Gateway orbital station, or one or more continuously occupied Moon bases.
Here is the CH4 pyrolysis reaction at 1200 degrees C:
6
CH4 → 6
C + 12
H2
Another atmospheric gas that must be closely regulated and cycled is N2. It is vital for two reasons. First, it dampens the combustion potential of a pure oxygen atmosphere. Second, nitrates are essential fertilizers for agriculture. Without it, colonists will be unable to grow the crops required to be self-sustaining.
Here on Earth, we tend to regard N2 as inert. We don’t metabolize it like we do oxygen. We even eliminate it in limited circumstances. Hospitalized patients in respiratory distress are routinely administered pure O2.
However, pure oxygen in a closed cabin is flammable. The tiniest spark will initiate a conflagration that will burn until all available free O2 is used up.
I recall the Apollo 1 training disaster, when an electrical short circuit aboard the command module started an onboard fire. Technicians stationed outside were unable to open the capsule hatch quickly enough before the exterior paint began to blister from the intense heat generated inside. Astronauts Virgil Grissom, Edward White and Roger Chaffee perished in this tragedy. Ever since, NASA has utilized cabin atmospheres comparable to natural air—79% N2, 21% O2. Without N2, any Mars colony is doomed to suffer the same fate as the Apollo 1 mission.
But N2 is a necessity for another reason. In a process called the nitrogen cycle, N2 is converted to nitrate salts (NO3-), usually by bacterial metabolism. Nitrates are used by plants to generate proteins, nucleic acids, and other nitrogen-containing compounds. In the absence of nitrates, higher forms of life are not possible.
While the percentage of atmospheric N2 is low on the Red Planet, 2.7%, it can be collected by compressing the thin Martian air and screening it out of the predominant CO2. Watch for future NASA unmanned Mars missions to evaluate N2 collection systems. I’ll discuss the nitrogen cycle and applications in more detail in an upcoming edition of JOTH.
I describe the closed system in my first book, Crimson Lucre.
In situ water is hydrolyzed for the Prospector Base air supply. The same process is performed externally to generate O2 and H2 for rocket propellant for the workhorse Ascent/Descent Vehicles.
In Crimson Lucre, the pyrolytic reaction chamber is hacked by shadowy Earthbound elements intending to destroy the facility. Only the quick thinking of commander Dallas Gordon prevents an explosion that would burst the base's inflated domes.
In my second book, Red Dragon, mission geologist Dave Caraway figures out how to combine the leftover graphene with perchlorate from water purification to create explosives for the mining operation. Those compounds are repurposed as defensive weapons against Pang Xianjing, who establishes a secret garrison to finish the job of eradicating Prospector Base.
Dave re-employs his explosive recipe in book four, Red Planet Lancers, to defend the permanent base, Ep City, against Emperor Zhang Aiguo’s invading forces.
Who knew chemistry could be so entertaining? But here in the real world, watch for the basic environmental systems I described, or some variant thereof, to be tested on the Moon and deployed on Mars.
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Want a deeper dive? Check out these sources.
https://en.wikipedia.org/wiki/ISS_ECLSS#:~:text=It%20uses%20electrolysis%20to%20produce,hydrogen%20is%20vented%20into%20space.
https://en.wikipedia.org/wiki/Sabatier_reactionhttps://www.space.com/16903-mars-atmosphere-climate-weather.html#:~:text=According%20to%20ESA%2C%20Mars'%20atmosphere,therefore%20cannot%20breathe%20Martian%20air.
https://www.nasa.gov/mission/apollo-1/#:~:text=Apollo%201%20Tragedy&text=AS%2D204).-,The%20mission%20was%20to%20be%20the%20first%20crewed%20flight%20of,the%20command%20module%2C%20or%20CM.
