Breathing easy on Mars: Three oxygen options for the red planet
Let’s face it, breathing is kind of a big deal. There is simply no way around it. Humans require a steady stream of oxygen rich air to ensure we can continue being alive. So generating Oxygen (O2) on Mars is one of those key technologies that must be included in the overall plan for visiting the red planet.
In this article we are going to look at the current available technologies, pros and cons for each, and the feasibility of these systems to be put into use in the near future. The research we have done at The Mars Blueprint indicates that there are three methods that are well understood, tested and (one) is already in use on Mars. The current oxygen generation options include CO2 electrolysis, CO2 Plasma Reactor, and H2O electrolysis.
As a baseline for O2 production requirements there are both human and rocket considerations. According to NASA, the average human consumes roughly 30-35g O2 per hour or 840 g per day/per person. On the rocket side of the equation NASA estimates 25 metric tons of O2 will be required to launch a rocket from the surface of Mars for the return journey to Earth. This means that a solid planning benchmark for O2 production is 1kg O2 per-day per-person throughout the mission and 25 metric tons for the rocket’s return trip. All three O2 generation methods have demonstrated they can scale up significantly as long as there are available raw materials and power. The planning factor we are using for power generation is a 35-40 KW capacity for the base. As we previously discussed, this is in the range of current technology and based on NASA estimates for the needs of an early Mars base. This represents the max power threshold and any O2 production systems must be optimized to use a fraction of this total amount to be feasible.
In order of most feasible and able to be deployed immediately, to least feasible and needs the most development or materials discover, the options are:
CO2 Electrolysis: NASA’s operational unit on Mars is producing 5.4 to 10 g O2 per hour from compressed/heated CO2 from Mars atmosphere at an energy demand of 300W.
Pros – Currently in testing on Mars on the Perseverance Rover and has demonstrated the ability to create breathable oxygen from the Mars atmosphere through splitting CO2 into O2 and Carbon Monoxide (CO).
Cons – System requires both significant pressurization and heating to convert CO2 into O2 and CO. The system is also susceptible to degradation over time due to contaminants building up on the electrodes and general wear.
Perseverance’s oxygen generation system is known as the Mars Oxygen In- Situ Resource Utilization Experiment (MOXIE). MOXIE is a proof of concept experiment that is already successfully producing breathable oxygen on Mars. The system works by pressurizing and heating the ambient Mars atmosphere and then running it across charged electrodes which split the CO2 into O2 and CO. MOXIE uses a max power consumption of 300W provided by Perseverance Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) and onboard batteries.
Feasibility (Ready to launch now – limited efficiency) An oxygen generation plant based on MOXIE is 100% feasible but would need to be increased significantly in both scale and power demands to meet required O2 output.
CO2 Plasma Reactor: a University of Lisbon prototype is producing 14g O2 per hour from simulated ambient Mars atmosphere at realistic temperatures and pressures and an energy demand of 300W.
Pros – The prototype plasma reactor is achieving a 30% conversion rate of CO2 to O2 producing more O2 per Watt than CO2 electrolysis. Plasma systems are also most effective at Mars ambient pressures requiring no pressurization or heating of CO2 to produce O2.
Cons – Plasma reactors designed to produce O2 are less mature technology and still largely laboratory prototypes. Also, system complexity saved on the front end in terms of pressurizing CO2 will still need to be built in on the output side to increase O2 pressure about 100x from Mars to Earth standard pressure for astronauts to breath.
The University of Lisbon system took a new approach and combined non-thermal plasmas and conducting membranes to break down CO2 into CO and O2 at a much higher rate than MOXIE. Their approach used an electron beam fired into a reaction chamber which resulted in about 30% of the CO2 converted into O2. The most recent operational device is still in laboratory testing but does show the potential to produce up to six times the oxygen that a MOXIE-like system could at the same power consumption. An added bonus is that the same reactor could be fed CO2 and H2 to produce methane (CH4) for use in rocket engines such as the SpaceX Raptor and Blue Origins BE4.
Feasibility (Major potential – Needs further development) An oxygen generation plant based on a plasma reactor could potentially produce more O2 than an electrolysis based system AND could be used for both O2 and CH4 production. If designs are further matured and miniaturized they could even allow astronauts to wear packs that convert CO2 to O2 to augment or replace pressurized tanks while working outside the habitat. All of these represent a major advantage but the system needs to be matured further to ensure it is durable, safe and reliable.
H2O Electrolysis: The Russian Electron-VM oxygen generation system on the International Space Station (ISS) uses an electrolyzer setup to generate 57g of O2 per hour from reclaimed water (H20) and an energy demand of 315W. The system is designed to increase production to 229 g per hour at 1500W.
Pros – Produces highest volume of oxygen of any system and variations of this design have been in operation on MIR and the ISS for decades. One liter of water produces up to 889 g of oxygen. Very mature technology and currently in use.
Cons – No dependable source of water on Mars is currently known. In-situ production of oxygen from atmospheric CO2 is far more economical at present until a large water source is found.
The ISS life support system currently uses two (one Russian and one U.S.) designed electrolyzers to turn reclaimed water into oxygen and hydrogen. The hydrogen is then combined with CO2 to produce water and methane using a Sabatier reactor and the water is again fed back into the electrolyzers for maximum oxygen production.
Feasibility (Major potential – Needs water source) ISS oxygen generation systems using H2O electrolysis have proven they are both reliable and able to produce large amounts of O2 consistently. This technology is the clear winner IF water is found in large accessible quantities as it would provide both oxygen and hydrogen which are needed for both breathing and creating rocket fuel.
Oxygen is life and creating it in-situ is the key to a successful manned mission to Mars. To survive and thrive on the red planet, we must develop technologies that enable in-situ production of critical resources such as oxygen. The current options for using either electrolysis or a plasma generator are extremely promising as two of the three designs are already in use in space or on Mars. The blueprint for Mars will need to include one or more of these technologies to ensure mission success.