The atmosphere and the lithosphere of Mars offer a plethora of resources that can be used in robotic and human missions to Mars. The utilization of Martian resources will be first initiated by robotic missions to demonstrate the feasibility of in-situ resource utilization (ISRU) before the first humans set foot on the planet. The Mars In Situ Propellant Production Precursor (MIP) (Figure 2-13) aboard NASA's 2001 Mars Lander and the proposed Mars In Situ Propellant Production Sample Return (MISR) Mission (Figure 2-14) are good examples of how this can be put into practice (D. I. Kaplan, 1999).

Secondly, robotic missions will provide supplies (propellant, consumables) for human missions. These robotic missions will also help to define the exact locations of the on-ground exploitation sites, either from Mars orbit (orbiter missions) or directly on the Martian surface (lander missions) to map and analyze the resources. The main resources that are considered for in situ resource utilization on Mars are the following:

• Water for human consumption and propellant production
• Atmospheric carbon dioxide for methane and oxygen generation
• Martian Regolith for infrastructure

Carbon Dioxide Electrolysis

Carbon dioxide electrolysis is a well-known process and can be described by the following chemical reaction

2CO2 ---> 2CO + O2

It is used to extract oxygen out of the atmospheric carbon dioxide by means of a yittria stabilized zirconia solid electrolyte. It is also known as "solid oxide electrolysis" (internet ref 1). The first in-flight test of this technology will take place in the course of the MIP experiment mentioned above. If the experiment is proved to be worthwhile, such technology shall recommended as part of our strategy to produce oxygen to be used as propellant.

Sabatier Process

The CO2 in the Martian Atmosphere will be used to produce methane by the so-called Sabatier process (discovered by the French chemist Paul Sabatier in the nineteenth century). The reaction converts carbon dioxide with hydrogen at elevated temperatures into methane and water (Stephen J. Hoffman, David I. Kaplan,1997):

4H2 + CO2 ---> CH4 + 2H2O

Since no hydrogen is found in the Martian atmosphere, the hydrogen has to be imported from Earth or from the Moon and NEOs. CH4/O2 rocket propellant only consists of 16% hydrogen by mass. Therefore, the reduction in mass that has to be brought from Earth to Mars is still substantial. A quick calculation shows that about 0.222 kg of H2 and 1.222 kg of CO2 are needed to produce 1 kg of water and 0.444 kg of CH4.

Methane and the oxygen can be used for several applications. The most obvious is probably the use as propellants for spacecraft and rovers. The feasibility and applicability of methane as rocket fuel can be assumed given the fact that a Russian company (Makeyev) is currently developing a launcher with liquid methane engines in order to decrease launch cost. The use of methane as rover fuel on the other side could eliminate the need for RTG or reactor powered rovers, and also avoids the limited range of battery powered rovers. If cryogenic methane and oxygen are used, than the rover could be propelled by a piston engine. Since no compression is required (the two liquids just have to be brought together and ignited), the engine would be very simple and robust. In a case of a complete failure of all life support systems and/or loss of the power system, the rovers and their propellants could be used as a survival cache for the crew. The crew will breathe the oxygen, and together with methane it can be used to produce power (for example in fuel cells). Apart from carbon dioxide, water would be a product of this reaction, which again can be consumed or be used otherwise by the crew in an open loop "survival" system. All these benefits can be achieved without the necessity of bringing huge quantities of consumables from Earth (Pauly, 1998).

Water Electrolysis

Water electrolysis is a well-known chemical process:

2H2O ---> 2H2 + O2

It can be employed to produce hydrogen and oxygen for use as propellants. In combination with a Sabatier reactor, the electrolyzer splits the water that comes out of the Sabatier reactor. The hydrogen hence produced is cycled back into the Sabatier process feed whereas the produced oxygen and methane remain as reaction products. NASA (during the 2003 Mars Lander Mission) will also demonstrate this combined technology (Figure 2-15).

The presence of water ice at the poles was proven by the Viking orbiters (1975) (Kieffer et al., 1992). This water could be extracted for sooner use. However, this would require missions to aim at the poles, which is not favorable, since the most interesting locations are away from the poles.

Despite the large uncertainties that still exist, a general picture has emerged of the distribution of underground ice on Mars that appears to be consistent with the current understanding of the major physical processes involved in geological formation. This picture is certainly consistent with the view that water has played a major role in the geologic evolution of the planet surface. Today, it is estimated that the total quantity of sub-surface ice is equivalent to a global layer of water approximately 500m deep (Marov, 1999).

The depth of which this permafrost can be found varies significantly with the latitude. Close to the poles the ice is probably very close to the surface, perhaps a few tens of meters at 35° North, and a few hundred meter at the equator (Kieffer et al., 1992). Therefore, the water ice could be mined with rigs that drill to the ice layers, melt the ice and then pump the water to the surface. Closer to the poles, surface mining becomes possible. Kieffer et al. also foresee the possibility of liquid subsurface water reservoirs. If these actually exist, the water mining becomes simpler, since heating is no longer required.

There is a great need for further investigation of the permafrost on Mars. These investigations could include deep penetrating radar, direct sampling (with penetrators or drills), and seismology. Missions like the Mars Polar Lander (currently on its way to Mars) and Mars Express (launch in 2003) could substantially to a greater understanding of the quantity and distribution of Martian ground ice and the processes that affected its evolution.

Using Martian Regolith

Among the available resources from the Martian regolith, minerals such as iron and silicon will be used for infrastructure manufacturing later in the exploration of Mars. Like the previously discussed options, these will also have a positive impact on the mission cost, just by reducing the launch mass. The Viking landers, which landed on Mars in 1976 have demonstrated the presence of iron and silicon in abundance (21% and 13% respectively by mass), assumed to be in the form of oxides, namely SiO2 and Fe2O3 (Kieffer et al.). The regolith can be used as shielding material without any preprocessing. It just has to be dumped over the habitats. The regolith also contains all the substances that are required for the soil to grow plants.

Phobos and Deimos

Other interesting objects for in situ resource utilization could be the Martian moons, Phobos and Deimos. Unfortunately one of the findings that were made by Pathfinder was that they are not carbonaceous chondrites as previously assumed. The current understanding characterizes them as putatively clay and organic rich D-like asteroids (S. Murchie et al., 1998). This group of objects is regrettably poor in water. But if this evaluation should be altered due to new scientific findings, these two objects certainly could become stepping stones for the exploration of Mars.

NEXT >