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obtained by optimizing all parameters with respect to particular system variables such as operating cost or mission performance criteria. Such optimization would have to include time dependent effects associated with coaxial plasma turbulence, and are not treated in this study. The pressure-temperature relationships in Figure 22 are indicative of the characteristics of a general plasma core reactor, as defined by the reference model in Chapter III. For a specific, well defined mission, the required rocket would very likely be based on a different plasma reactor model. In this case, the pressure-temperature trajectories would differ quantitatively from those in Figure 22.

        For centerline temperatures above 50,0001K, it was

necessary to add as much as 15% seed material to the uranium fuel in order to depress the temperature before reaching the higher density region of the seeded hydrogen. The temperature calculations indicate that the achievement of a desired temperature profile is a delicate balance between the radial distributions of uranium (which both produces heat and absorbs radiation), and seeded hydrogen (which absorbs radiation). Heavy seeding of the hydrogen will be made at the expense of reduced specific impulse, since any seed material will presumably be exhausted, and thereby increase the mean mass of the propellant.