In addition to the primary liquefaction requirements, refrigeration is also required to re-liquefy vapor that might be boiled off during long term storage. How much loss this boil off will entail has not been calculated. Also, CO could not be stored at a high enough temperature to eliminate the possibility of atmospheric CO2 condensation. Propellant liquefaction power requirements are substantial and merit more detailed consideration than was provided in the present work. However, some interesting observations can be made. First, in those systems where propellant is not produced in the proper O/F ratio desired, but rather in the stoichiometric ratio, there is adequate cooling capacity available from evaporation if the excess fuel (or oxidizer) is boiled off to leave the remaining propellant near one atmosphere and its normal boiling point. Second, considering the enormous amount of power the simple considerations used in this paper lead us to calculate for hydrogen liquefaction and refrigeration, the design of the hydrogen liquefier is central to any plant producing hydrogen for fuel use. Third, substantial power savings were realized by considering slightly subcritical storage. This implies that pressure is an important design variable, and designs at arbitrarily selected pressures may be far from optimum. Chemical Processes And Flow Diagrams A number of chemical processes are discussed here, all of which produce oxygen. They may also produce various fuels. Ifno source of hydrogen (e.g. water) is available, the oxygen would have to be produced directly from atmospheric carbon dioxide. This can be done using a solid oxide electrochemical cell. The reaction takes place, and the oxygen is produced by application of a potential across the solid oxide electrolyte. A byproduct of this process is CO, which may be used as a fuel when separated from any unreacted CO2 (note that these equations contain molar stoichiometric coefficients, not the masses typical of O/F ratios). If hydrogen is available (either transported from Earth or produced from water on Mars), then a different process can be employed to produce oxygen. The Sabatier reaction can be used as follows: The water is separated from the CH4 in a condenser. It can then be dissociated using water electrolysis to produce O2 and H2. The hydrogen can be recycled back into the Sabatier reactor. This process also provides methane fuel. In addition, it is possible to react carbon dioxide and hydrogen in a zirconia cell to directly produce methane and oxygen as demonstrated by Gur, Wise, and Huggins [25]. This process eliminates the need for the water electrolyzer and simplifies the plant design.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==