essentially unaffected (3-7 K) by day-night temperature changes and which give very high efficiencies. The radiating efficiencies are 96% and 91% or 444 and 418 W/m2 at 308 K for the two best cases. These are the horizontal radiator with a vertical shield and the radiator at a 45° slope with an aluminum shield, respectively. This compares to a theoretical efficiency of 459 W/m2. A third case using an active sunshield was developed for equatorial regions and has an efficiency of 86% with a radiating power of 395 W/m2 and a nighttime temperature of 296 K. The use of vertical radiators, even when shielded, was not attractive because it was not possible to shield the radiators from direct sun and soil radiation at the same time. The calculated value of 150 W/m2, for a full sunshield was mitigated by the use of both sides to a tolerable 300 W/m2, but the extra area was very detrimental to day-night stability with a nighttime equilibrium temperature of 232 K. A minimal sunshield of 12% of the radiator area improved the radiative power to 415 W/m2 using both sides and the nighttime temperature improved to 252 K at the cost of more daytime and seasonal variability. It should be noted that previous work [2] on liquid droplet radiators did not take into account re-emitted and reflected radiation from the underside of the sunshield and used a radiating power of 694 W/m2. Use of the optimistic number above would mean increasing the area by 67% which is feasible by increasing the height of the radiator to 100 m. The resulting 10% increase in mass is due to the collector which would have to be 1.67 times wider and the structure which would have to be higher and stronger. Two types of surface finishes could be used on the sun shields, a white solar reflector, MgO, and a metallic reflector, vacuum deposited aluminum on mylar. Use of these surface finishes in appropriate combination was critical to the improved performance of the radiators. The mass of the sunshields is considered equivalent to a conservative solar sail design of 1 g/m2 for a total mass of 25 kg. Supports can be fabricated from pipes and guy wires can be made from glass fiber, but another 25 kg is estimated for imported hardware to be on the safe side. The equatorial radiator requires a more extensive structure for the active sunshields and an additional 500 kg is estimated if all the structure is imported. The towers could be made from locally produced pipe which would cut the import mass to 100 kg. Two types of ceramic radiator were studied: one fused in place, and one fabricated of glass pipe. The melt-in-place radiator had the advantage of simplicity and low imported mass. It was remarkably insensitive to the required regolith melting temperatures (1700-2000 K). Not being reinforced it had to be thicker than the glass pipes. The fabricated pipe required beneficiation to produce matrix and fiber fractions, and a processing plant. The pipe was stronger, much tougher and thinner than the melt-in-place glass plate. Good mass estimates were available for the pipe processing
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