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Phase II Final Report - NASA's Institute for Advanced Concepts

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Chapter 3.0 Vehicle Design<br />

3.5 Fuel Storage and Production<br />

Mars [199]. However, insufficient in<strong>for</strong>mation is available to determine if the potential water<br />

could be extracted and utilized by the Entomopter system <strong>for</strong> fuel production. There<strong>for</strong>e, the fuel<br />

selection and analysis will be based on the need to provide hydrogen from Earth. As more in<strong>for</strong>mation<br />

is obtained on the potential of utilizing the subsurface water on Mars, the results of this<br />

selection process may change.<br />

The remaining elements that make up the fuels listed in Table 3-16 are present on Mars with the<br />

exception of fluorine. The lack of fluorine, as well as the scarcity of chlorine, eliminates the following<br />

four propellants as potential candidates <strong>for</strong> fueling the Entomopter: Monomethyl hydrazine<br />

and chlorine trifluoride, monomethyl hydrazine and IRFNA, UDMH and chlorine<br />

trifluoride, RPI and IRFNA. Also HAN and the HPB monopropellants were eliminated due the<br />

complexity in their chemical makeup, which would be very difficult to manufacture.<br />

Because the remaining propellants all require hydrogen (which must be brought from Earth) the<br />

next step is to determine which of these propellants minimize this hydrogen requirement.<br />

Table 3-17 shows the percentage of hydrogen on a weight basis <strong>for</strong> the candidate fuels.<br />

Table 3-17: Percent of Hydrogen by Weight <strong>for</strong> the Various Candidate Propellants<br />

Fuel/Oxidizer<br />

Chemical Makeup<br />

Percent Hydrogen by<br />

Weight<br />

Monomethyl Hydrazine and Nitrogen<br />

Tetroxide (N2H6C)+2(N2O4) 2.61%<br />

UDMH and Nitrogen Tetroxide (N2H6C)+2.7(N2O4) 1.96%<br />

Hydrogen Peroxide (0.9H2O20.1H2O) 5.38%<br />

Ethylene Oxide (C2H4O) 9.09%<br />

NitroMethane (CH3NO2) 4.92%<br />

n-Propyl Nitrate (C3H7NO3) 6.66%<br />

Based on Table 3-17, the primary choice to minimize the need <strong>for</strong> hydrogen is the bipropellant<br />

UDMH with nitrogen tetroxide. However, a bipropellant system will increase the complexity of<br />

the overall mission. It will require two separate production plants, one <strong>for</strong> the fuel and one <strong>for</strong><br />

the oxidizer, as well as separate storage and fueling ports. Unless engine per<strong>for</strong>mance becomes a<br />

significant issue, the primary choice <strong>for</strong> the propellant will be a monopropellant that significantly<br />

reduces the complexity of the production system.<br />

Overall, the propellant selection can be narrowed to four potential candidates, two bipropellants<br />

and two monopropellants: monomethyl hydrazine fuel and nitrogen tetroxide oxidizer, UDMH<br />

fuel and nitrogen tetroxide oxidizer, hydrogen peroxide and nitromethane. Ethylene oxide and n-<br />

propyl nitrate were eliminated as potential fuels due to the relatively higher percentage of hydrogen<br />

content. Of these remaining four fuels, hydrogen peroxide is the primary candidate <strong>for</strong> production<br />

on Mars.<br />

177

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