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NASA Innovative Advanced Concepts

Cryogenic Selective Surfaces

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Cryogenic Selective Surfaces
During our Phase 1 NIAC study we discovered a novel coating we call “Solar White” that, when used in deep space, is predicted to reflect more than 99.9% of the sun’s energy. We have shown analytically that a sphere covered with a 10 mm thick coating of Solar White and located far from the Earth and at 1 Astronomical Unit from the Sun can achieve a steady state temperature below 50 K, the freezing point of oxygen. The ramifications of such a coating are broad and significant, ranging from enabling long-term cryogenic storage to allowing passive high temperature superconductor operation in space. However, the development of these coatings is only at a theoretical modeling stage. The next two significant steps required to advance this breakthrough technology are to fabricate these coatings and test their performance. Construction of rigid versions of the coatings may be difficult, because they are composed of only one material deposited onto a metallic reflector, though there are precedents such as rigid foam and Space Shuttle Tiles to use as models. We have access to chemistry and materials experts who will work on constructing the coatings and we will liaise with Ames Research Center to help leverage the expertise available at that NASA center. Testing of our algorithms can be performed in parallel because we can construct non-rigid versions of the Solar White Coating consisting of powdered materials sandwiched between a mirror and a cover slide as a test sample. Testing would occur in a simulated deep space environment, which we will create using a vacuum chamber, a 20K cryo-cooler, and an irradiance source. By monitoring the difference in steady-state temperature in the test sample with and without irradiated energy and comparing this against our algorithmic predictions will be able to refine our models of these novel coatings when exposed to solar and infrared irradiance. We have shown in our Phase I effort that the use of Solar White could theoretically allow liquid oxygen to be maintained on a long duration mission to Mars. The Solar White coating does this by reducing not only solar heating, but also radiative heating from other, warmer, portions of the Mars vehicle and conductive heating along support struts and flow lines. We now propose to extend the deep space cryogenic use of this exciting new coating by examining the storage of LOX on the Moon. We will also examine the use of Solar White on a LOX/LN2 deep space storage depot and determine the possible locations of this depot relative to infrared emitters such as planets and moons, as well as the Sun and nearby space vehicles. More »

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