Mars Atmospheric Resources


Upon reaching Mars, we again have a world with resources that can be used to expand our capabilities. The martian atmosphere, consisting mostly of carbon dioxide, can be processed to release oxygen for life support or propellant use. Carbon monoxide, which could be a moderate performance rocket fuel, is the coproduct. By combining this oxygen with a small amount of hydrogen, water for a variety of uses could be produced for only a fraction of its mass if brought from Earth. One good aspect of atmosphere utilization is that no mining is involved. Simple gas handling equipment can be used, providing a much more reliable system.

Life support technologies routinely deal with the conversion of CO2 to other compounds, including methane. This process was discovered nearly one hundred years ago and is still used in many chemical plants today. A direct application of this technology to the martian atmosphere would allow for the production of oxygen, methane, and water by bringing only a small amount of hydrogen. Thus, large quantities of propellant could be leveraged from minimal import mass. As described earlier, a rocket engine using methane and oxygen could be developed for use in both lunar and martian spacecraft. This could enable another large cost savings for the SEI by utilizing those materials available at the Moon or Mars.

Planetary scientists agree that water is available at the poles of Mars in the form of ice. It is likely, but not certain, that water is available elsewhere on the planet, perhaps as a permafrost layer or bound as a mineral hydrate. If the robotic missions in the early stages of the SEl provide evidence of water, there is every reason to believe that a process can be developed to make it available for human use. It is likely that one could even extract enough water to produce both hydrogen and oxygen propellant for the launch back to orbit and even the return trip to Earth, thus reducing the size of the spacecraft leaving Earth for Mars. Telerobotic mining at distances as far as Mars is not practical, however, and totally automated systems would need to be developed. And, at the more accessible latitudes near the equator, any water is likely to be found at a lower depth, compounding the problem.

The two moons of Mars, Phobos and Deimos, may also be rich in water. Processing at the extremely low gravity present on these bodies will require some innovative equipment. While early exploration scenarios suggest it would be difficult to bring this promise to fruition, future operations on or near Mars could easily make use of the potential within these bodies. Many asteroids are believed to be of similar composition and are also likely targets for utilization once we have honed our ability to operate highly complex equipment at distances so remote that teleoperation is not feasible. For the near term, however, the SEI requires the development of an ISMU program which focuses on the Moon and Mars.

Olympus Mons, a volcano on Mars, is 15 miles high and .~75 miles across at its base, dwarfing all other known volcanoes in the solar system. This view shows the caldera protruding through a cloud layer in the northern hemisphere of Mars. The presence of an atmosphere provides a Mars program with a resource unavailable at the Moon. Chemical procedures exist to convert carbon dioxide, which is 95 percent of the atmosphere, into products such as oxygen, water, and methane.

Carbon Dioxide as a Raw Material

The carbon dioxide (CO2) that makes up 95 percent of the atmosphere of Mars can be a valuable starting material for the manufacture of critical products. Unlike lunar resources, CO2 can be had by merely compressing the atmosphere. Carbon dioxide itself can be used to support plant growth at an advanced outpost. Both carbon and oxygen are important elements which have many possible uses at an outpost. There are several well understood chemical reactions that we can use to produce oxygen, methane, water, and perhaps other materials.

Oxygen can be produced by passing CO2 through a zirconia electrolysis cell at 800 to 1000deg C. Twenty to thirty percent of the CO2 dissociates into oxygen and carbon monoxide. Separation is accomplished by electrochemical transport of oxide ion through a membrane. A prototype reactor using this chemistry has been run for over 1000 hours. Using such a scheme, we could bring a small unit to the surface of Mars which would then continuously make oxygen for life support, propellant use, or further processing. The only additional item we would need to supply is the power to run it: a 12kW unit would produce about one metric ton of oxygen per month.

This oxygen can be converted into water if we also bring a small supply of hydrogen. Since the molecular weight of hydrogen is 2 and the molecular weight of water is 18, we can leverage 2 kilograms of hydrogen into 18 kilograms of water. The mass savings would, at some manufacturing rate, pay back the mass of the oxygen production unit. After that, we would get water for only the price of getting the hydrogen to Mars.

2CO2 --> 2CO + O2
zirconia electrolysis

O2 + 2 H2 --> 2 H2O
combustion of hydrogen

If we choose to import hydrogen, there are other things we can do with it in addition to making water. A chemical reaction which converts CO2 into methane (CH4) was discovered in 1899. This is known as the Sabatier reaction. Along with the CO2, hydrogen is passed over a finely divided metal catalyst at an elevated temperature. Methane and water vapor are produced. By taking this water vapor and splitting it to obtain oxygen and hydrogen (which is recycled), we can completely convert the imported material into 4 times its mass of fuel. We also get the oxygen we need to burn this fuel in a rocket engine, fuel cell, or internal combustion engine. When combined with the production of additional oxygen via the zirconia process described above, only 4 kilograms of hydrogen can be converted into 72 kilograms of a rocket propellant mixture.

CO2 + 4H2 --> CH4 + 2H20
Sabatier Reaction

2H20 --> 2H2 + O2
Electrolysis

CO2 + 2H2 --> CH4 + O2
Net Reaction

Other well known reactions have been practiced for decades which can also accomplish similar conversions. Fischer-Tropsch chemistry is practiced in the petrochemical industry in a variety of ways. It converts carbon monoxide and hydrogen into methane and water. The Bosch reaction can convert CO2 and hydrogen into carbon and water. The carbon could, perhaps, be used for advanced material production at an outpost once fabrication facilities are available.

Eventually, we will obtain water from the environment of Mars. We would then not need to make water from imported hydrogen. Indeed, we could turn the situation around and use this water as a source of hydrogen, thus continuing to utilize the chemical processing capabilities we have developed. For instance, it would be even more favorable to produce methane from the atmospheric CO2 and water derived hydrogen. This would require the production of much less water than if we switched the space transportation system to a hydrogen-oxygen propellant system. It is also much easier to liquefy methane than hydrogen.

With a large amount of hydrogen available, and a ready supply of CO2, we may consider going the next step and developing the ability to produce a large variety of products. If ethylene were produced from hydrogen and a carbon source, polyethylene can be made using technology available today. This material, or other carbon-based polymers, can then be extruded or molded to form habitats, furniture, pipes, and a variety of useful items. The petrochemical and natural gas industries can contribute a great deal of expertise in this area.