Feasibility study of water vapor adsorption on Mars for in situ resource utilization

Abstract

This paper presents the results of a feasibility study of the extraction of water vapor by adsorption from the Martian atmosphere, for in situ resource utilization (ISRU) purposes. Past proposals for extracting atmospheric water have invoked a compression-cooling process, which requires a prohibitively high specific power input. At the University of Washington the Water Vapor Adsorption Reactor (WAVAR), a highly effective water extraction concept based on adsorption processes in zeolite molecular sieves, is being developed. In this device, Martian atmosphere is forced over a zeolite bed which adsorbs the trace water vapor. Once the zeolite bed is saturated, it is removed from the flow, placed in a sealed chamber, and the water vapor desorbed by microwave heating of the bed, all in a continuous batch process. The water vapor thus obtained is condensed and electrolyzed into H2 and O2. The H2 can be combined with the atmospheric CO2 in a Sabatier reactor to produce CH4 and additional water that is recycled. The resulting ratio of O 2 to CH 4 is 4.0, very close to the optimum ratio of 3.5 for a CH 4/O2 rocket. Based on the encouraging performance comparison of the WAVAR concept with the compression-cooling process, a detailed simulation was run, using the first 250 sols of Viking Lander 1 meteorological data. A successful preliminary experiment on the microwave reactivation of the molecular sieve, zeolite 3A, was performed as well. The use of realistic Mars atmospheric data, however, highlighted the importance of landing site selection when using the WAVAR, as available atmospheric water quickly becomes minuscule if the ambient temperature drops below about 200 K.