Effective Purging of High-Performance Multilayer Insulation Systems

Abstract

The majority of insulation systems considered for long-term storage of cryogenics in space are multilayer types. These types consist of multiple radiation shields which often utilize low-conductivity spacer materials to maintain shield separation. High-thermal-performance multilayer systems require operation in a vacuum in order to eliminate gaseous conduction within the insulation. During ground-hold operation the condensible gases within the individual layers must be removed prior to cryogen loading. This is necessary to prevent the formation of solids, which can be detrimental to the insulation, Two methods for removing the condensible gases are commonly considered by industry. The first employs a vacuum bag around the insulation. The gases within the insulation are then pumped from the bag. The second method uses a purge bag around the insulation; however, in this method a noncondensible gas is circulated within the bag and insulation until a negligible quantity of condensible gases remains.