Fig. 4 represents the development of the heat flow from the storage unit to the Stirling heater during the orbital eclipse. The curves do not cross the horizontal line of the desired value at x = 0.5 because THe was matched to yield the desired heat flows at x = 0.5 during the insolation rather than the eclipse periods. This and the much larger thermal conductivity of LiF in the solid than in the liquid state near the phase change temperature, are the reasons that the discharge curves for all three cases are below the desired values. The addition of the intermediate heat pipe makes the difference less marked but to an insignificant extent. The reduction of the heat resistance to the He flow increases the difference to a seemingly unacceptable extent. In these three cases, it will be necessary to choose a lower THe for the eclipse part of the orbit than for the insolation part, in order to move the discharge curves closer to the desired value. One might even make a point-by-point adjustment of THe such that the charge and discharge curves of Figs. 3 and 4 coincide with the respective desired constant values. This adjustment for the eclipse period is given in Fig. 5 for Cases (1) and (2). The design of the heat pipe requires an approximate knowledge of the expected operational vapor temperatures Tj of its working fluid. Fig. 6 shows the development
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