Propellant Choices and Their Performance In order to select a propellant combination for manufacture on the surface of Mars, an important and limiting consideration is the availability of suitable resources. Based on the available resource pool there are several candidate fuel/ oxidizer combinations. The most readily available resource on Mars is its atmosphere, since carbon dioxide can be used as a feed stock. Atmospheric carbon dioxide can provide oxygen for use as oxidizer, and can provide carbon for hydrocarbon fuels. The necessary hydrogen would be derived from terrestrial or Martian sources. In addition, a byproduct of oxygen production from carbon dioxide might be carbon monoxide, which itself could be used as a fuel. All of the chemical processes considered here would produce oxygen as the oxidizer. The oxygen is produced at the Martian surface using the atmosphere, or possibly local water, as a feed stock. A solid oxide electrolytic cell can separate oxygen from atmospheric carbon dioxide, or standard water electrolysis techniques can be used to obtain oxygen from water. In addition to oxidizer, a fuel must be selected. We have chosen to discuss H2, CH4, and CO. Acetylene, C2H2, has also been discussed in this context [8], but we chose not to consider it due to difficulties with production, handling, and storage. The fuels selected offer useful performance and O/F ratios, and could be relatively easy to manufacture using local Martian resources. The fuel/oxidizer combinations to be compared in this paper and the feed-stock each would employ are listed in Table 1. The fuels are either manufactured on Mars (from local or imported feedstocks), or are brought from Earth to be used with Mars produced oxygen. The relative performance of these fuel/oxidizer combinations vary. The estimated peak impulse for each fuel is shown in Table 2, along with optimum O/F ratio. We assumed engines operating at about 200 psi, area ratio of 200, and have taken values by analogy to existing engines, or from other estimates. No effort was made
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