Hybrid Aerogel-MLI Insulation System Performance Studies for Cryogenic Storage in Space Applications
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Hybrid Aerogel-MLI Insulation System Performance Studies for Cryogenic Storage in Space Applications By: R. Begag 1 , S. White 1, J.E. Fesmire 2 , and W.L. Johnson 2 1 2
Aspen Aerogels, Inc., 30 Forbes Rd., Northborough, MA 01532 NASA Kennedy Space Center, Cryogenics Test Laboratory, KSC, FL 32899
ABSTRACT Long duration storage of large quantities of cryogenic fluids for propulsion, power, and lifesupport is an essential requirement for missions into space. Efficient and reliable insulation materials are key to the success of these missions. The required insulation material must outperform the current standard multi-layer insulation (MLI) for thermal insulation and provide additional features such as durability, micrometeoroid orbital debris protection, and flexibility, all in one single-layer material. Ultra-low density and highly hydrophobic fiber reinforced aerogel material integrated with MLI has the potential to offer a great insulation package which will overcome several issues that the current standard MLI alone suffers from such as: 1) damage during installation, 2) high cost, and 3) degradation over time. The hybrid aerogel/MLI solution affords a more reliable alternative because it is robust, and will outperform the MLI in cases of vacuum loss. Low density and highly resilient methylsilicate aerogel will contribute less solid conductivity to the overall heat transfer within the aerogel/MLI system. Sol-gel optimization of low density and low dust methylsilicate aerogels will be presented. Thermal performance of two prototypes of hybrid aerogel/MLI composites and a baseline MLI system (1 inch thick, 90 layers) fabricated by Aerospace Fabrication and Materials (AFM) and tested at cryogenic temperatures under different vacuum level conditions (at Cryogenic Laboratory, NASA KSC) will also be presented. INTRODUCTION The planned Altair/Ares missions to return to the moon include a short-term commute to and from the moon and an extended lunar stay of 210 days. Long duration storage of large quantities of cryogenic fluids for propulsion, power, and life-support is an essential requirement for these missions 1,2 . Several analytical and experimental studies were conducted over the last several decades which investigated a variety of methods for meeting mission storage requirements2, 3 . These methods can be divided into two general types: those that use boil-off gasses from the cryogen and those that have zero boiloff. Methods that utilize boil-off for cooling include thermodynamic vent systems and vapor cooled shields, each of which require additional fluid mass to compensate for the boil-off losses. Methods that enable zero boil-off include actively cooled shields that use a cryocooler refrigerator and a simple, well-insulated tank. The required insulation material must outperform the current standard multi-layer insulation (MLI) for thermal ⎯⎯⎯⎯⎯⎯ 1 2
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insulation and provide additional features such as durability, micrometeoroid protection, and flexibility. Aspen
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