Mining the Martian Regolith for Water

摘要

It has been thought for some time now that the human exploration of Mars will depend ultimately on our ability to utilize Martian resources. Zubrin's Mars Direct (Zubrin, 1992) and NASA's Reference Mission for the Human Exploration of Mars (Kaplan and Hoffman, 1997) both assumed that propellant and life support consumables could be obtained from the atmosphere of Mars. Various approaches to utilizing the Martian atmosphere as a source of oxygen have been studied, along with the reduction of CO_2 to methane, but in all cases it has been assumed that hydrogen must be brought from Earth. This is not an overwhelming problem, as the hydrogen is only a small part of the total propellant requirement (1/12 in the case of CH_4-O_2; 1/9 in the case of H_2-O_2). However, even this is a burden because hydrogen tanks generally are about as massive as the hydrogen they contain and either power or multi-layered insulation or both have to be provided to keep hydrogen liquefied from Earth to Mars. This reduces the effectiveness of propellant production on Mars, but it is still enabling for some missions for the Mars to orbit leg of the return home. A readily available source of water can be very beneficial to the performance of missions to Mars, by removing this dependency on imported hydrogen. Ultimately, large sources of water are available on Mars. Water in the polar icecaps, in permafrost, and potentially as liquid water below permafrost in special layers should be relatively easy to extract for use by human missions. However, these deposits are either in places where they are difficult to get to or where humans will probably not venture for a long time. Any source of water on Mars has to be readily available practically anywhere on the planet, if it is to be useful to humans early in a human exploration program. The atmosphere can be a source of water, if mass- and energy-efficient extraction techniques can be devised. There is a very low concentration of water in the atmosphere that is variable seasonally and with latitude. Coons et al (1995) proposed to extract water from the atmosphere by temperature swing absorption techniques, taking advantage of the dayight temperature differences. In their process, a suitable molecular absorber is opened to the atmosphere at night, from which it absorbs water. In the daytime, the path to the atmosphere is closed and the water is desorbed into a receiving vessel. The efficiency of the process is highly dependent on atmospheric humidity and nighttime temperatures and therefore on altitude, latitude and season on Mars. The principal performance considerations are the mass of the absorbent and the power required for pumps. It may not be competitive with imported hydrogen at some sites, but may work well at others.