Radiator Configurations Four configurations are shown in Fig. 3. Vertical Radiator The vertical radiator is superficially attractive because it can radiate from both sides, however it is not possible to screen the radiator from reradiation from the lunar surface or to completely block the sun. It is possible to block the peak sun periods and to reduce reradiation by covering the soil near the radiator with a lightweight reflector [2]. If it is attempted to block more sunlight by use of a larger sunscreen then the bottom of the sunscreen interferes with radiation from the radiator and re-emits radiation picked up from the Lunar soil. Such a radiator requires a complete radiation analysis over the solar day and it must also take into account the tilt of the lunar pole and the variations in the angle of inclination of the moon’s orbit relative to the ecliptic. The tilt of the poles is only 1.53° but the maximal orbital inclination is 5.32° for a total of 6.85°. Performance of this style radiator will vary during the day-night cycle and with the seasons. Radiating power varied from 300 W/m2 with a sunscreen equal to the radiator area to 414 W/m2 for a minimal sunscreen of 12% of the area. The major problem with this system is its nighttime performance—the equilibrium temperature varied between 232 K and 252 K. Inclined Radiator The inclined radiator can be completely blocked from the sun if the angle of slope is great enough for the latitude. To guarantee complete blockage of the sun at all times we must take into account the effect of the above 6.85° variations due to inclination of the poles and the orbit. Thus at a latitude of 52° the required angle is 90-52°+ 6.85° = 45. The sun will shine on the opposing bank but this surface can be modified with a coating to reduce the reradiation effect. Calculations have been done with a solar reflector, MgO, and a metallic reflector, vacuum deposited aluminum on mylar. Radiating power varied from 383 W/m2 for the solar reflector to 418 W/m2 for the aluminum reflector. The equilibrium nighttime temperatures are 294 K and 301 K, respectively, which is an acceptable swing and well above freezing. Since these surfaces are both reflectors it is important that the solar radiation be reflected away from the radiator therefore the angle between the two slopes should be greater than 90°. Horizontal Radiator A simple design uses a horizontal radiator coated with a solar reflector. Reradiation from the soil is avoided by the horizontal location and the radiating power is a reasonable 257 W/m2 but the nighttime temperature is 266 K which is below freezing. Horizontal Radiator with Vertical Sunshield Modifying the above design with a sunshield gives several benefits. The sunshield blocks the sun and although it also absorbs reradiation from the lunar soil it can be made to preferentially radiate it away from the radiator.
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