Ceramic matrix composites (CMC) could enable air-breathing hypersonic vehicles to be developed because of their light weight and high temperature resistance. However, limited fabrication capabilities are preventing the material's use in aerostructures, says NASA Langley Research Center-based thermal protection systems (TPS) and hot structures expert David Glass.

Glass reviewed a range of materials in a lecture at the recent American Institute of Aeronautics and Astronautics' space planes, hypersonic systems and technologies conference in Dayton, Ohio.

According to Glass, CMCs meet the challenges of hypersonic transport, including construction of a vehicle and its propulsion system that is light enough to propel a useful payload above Mach 5, while also being sufficiently heat-resistant to cope with repeated long exposure to very high temperatures.

Sceptical that possible alternatives such as ultra-high-temperature ceramic materials, under study by Italy's aerospace research centre CIRA, are a long-term solution, Glass says: "CMCs will enable air-breathing hypersonic vehicles once they can be used to fabricate all the structures."

But he admits that the main obstacle to the use of CMCs is the need to develop the tooling and processes for economically fabricating large, thick, CMC structures with complex curves, which would not be susceptible to delamination.

NASA administrator Michael Griffin said in December 2007 that he thinks disposable TPS structures for reusable spacecraft are an option that should be explored. Glass agrees that for wing leading edges a detachable, disposable TPS structure could work, but doubts that it would be possible for TPS acreage that would cover a re-entry vehicle's leading surface.

Source: Flight International