Evaluation of Design Concepts and Integrated Materials for Efficient Airframe Structures

Present space vehicles such as NASA’s space shuttle and reentry bodies are designed with a cool internal structure, typically aluminum, surrounded by a parasitic thermal protection system (TPS). The space shuttle TPS uses coated carbon-carbon silica tiles and aluminum blan-kets, while reentry bodies use carbon/phenolic or silica/phenolic ablators. These designs are in-herently heavy and structurally inefficient. Future vehicles can be improved through the use of warm or hot structures in which the TPS in mechanically integrated with the airframe, for exam-ple as a sandwich structure with a hot erosion resistant outer skin, an insulating core, and a warm, load-bearing inner skin. A sandwich construction is structurally very efficient as evi-denced by its use in almost all commercial and military aircraft. However, several challenges must be met to translate this technology into practice for reusable hypersonic and reentry vehi-cles. These include issues associated with high transient heat loads, a severe thermochemical environment, thermostructural interactions among dissimilar materials, heat transfer versus load path, acoustic behavior, and fabrication of large high temperature structure, attachments, and seals. Due to the complexity of the problem this Phase I proposal focuses on a design and analysis effort, with the fabrication and testing tasks planned for Phase II. The behavior of the airframe structure depends upon parameters associated with the vehicle mission, trajectory, local geometry, and location on the body. For this reason we feel it is premature to fabricate and test materials in Phase I, since teaming with a fabricator will automatically constrain the design space to specific materials and processing methods. The proposed Phase I tasks include: 1) Design Goals and Environmental Conditions, 2) Integrated Material and Structural Concepts, 3) Material Property Database, 4) Thermostructural Analysis, and 5) Fabrication and Characterization Plan. The goal of the Phase I effort is to identify several design concepts that address the needs of in-tegrated airframes for both hypersonic and reentry vehicles. The designs will address leading edges, control surfaces, and large acreage windward and leeward locations. These designs will provide the foundation for fabrication and testing tasks that will be undertaken in the Phase II program. Materials Research & Design (MR&D) is uniquely suited to this project. The senior staff each has over 25 years of experience in the design and analysis of materials for extreme envi-ronments. MR&D is not a fabricator so we are not compelled to force a particular material into an improper design. However, MR&D has established a strong professional working relation-ship with multiple members of the advanced materials community so it is well positioned to cre-ate a Phase II team that can fabricate and characterize the design concepts developed in Phase I.