Honeycomb sandwich structure for future space transportation systems with integral cryogenic tankage

This paper presents the status of the structural development of an integral cryogenic-tankage/hot-fuselage concept for future Space Transportation Systems (STS). The concept consists of a honeycomb sandwich structure which serves the combined functions of containment of cryogenic fuel, support of vehicle loads, and thermal protection from an entry heating environment. The inner face sheet is exposed to a cryogenic (LH2) temperature of -423°F during boost; and the outer face sheet, which is slotted to reduce thermal stress, is exposed to a maximum temperature of HOOT during a high-altitude, gliding entry. A fabrication process for a Ren£ 41 honeycomb sandwich panel with a core solidity less than 1% has been developed, which is consistent with desirable heat treatment processes for high strength. Preliminary structural allowables and thermal properties for use in structural system studies have been determined; two 1 x6 ft panels have been tested with combined thermal and mechanical loads; and the effects of slots used to reduce stresses in the outer face sheet on the lower surface of the vehicle have been evaluated in the cryogenic environment associated with containment of LH2 fuel. Based on the work presented in previous system studies and the hardware development described herein, the Rene' 41 honeycomb sandwich appears to be a viable structural concept for an integral cryogenictank/hot-fuselage structure; however, additional in-depth studies, hardware development, and testing are required to verify the concept fully.