and that top priority should be given to overcoming the technology barriers that will have the largest impact on future weapons systems. As indicated in that report, these barriers include the following: compressor discharge temperature limits; turbine inlet temperature limits; high-temperature, high-heat-sink fuels for thermal management; lightweight structures; and signature control.

The technology challenges in developing future military aerospace propulsion systems are significantly materials challenges. Overcoming these challenges will require focus on a systematic materials approach and materials R&D specific to the needs of the subsystem involved. Such considerations would include the following:

  • Materials for atmospheric propulsion systems, both air-breathing and alternate systems;

  • Materials for space propulsion systems;

  • Materials for alternative fuel engines;

  • Materials for the development of lightweight and multifunctional systems;

  • Materials methodologies for stealthier (signature controlled) systems; and

  • Strategies to coordinate the development of materials, composites, and interactive materials systems that will work together to create an effective and efficient multifunctional materials palette.

These materials issues will require that the DOD take new R&D directions and, in that context, the NRC was asked by the DOD to conduct the present study to assess the needs and directions for a national materials R&D strategy to respond to the challenge of developing materials for future military aerospace propulsion systems and to keep the United States on the leading edge of propulsion technology.

1.2
FUTURE MILITARY AEROSPACE PROPULSION NEEDS

Capabilities-based planning addresses the uncertainty in the threat environment by using a wide range of scenarios to bound requirements for future systems. The DOD introduced this approach several years ago as the planning approach to be used for justifying military needs, but at the present time this planning approach is not sufficiently mature to have identified stated needs. However, the 2006 NRC study referred to above—A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs—identified global strike, global mobility, airborne C4ISR (command, control, communications, computers, intelligence, surveillance, and reconnaissance), and next-generation space access as required capabilities. These capabilities require technology advances in high-speed turbine engines, ram/scramjet/pulse detonation engines, rocket propulsion, combined-cycle engines, and ultra-efficient propulsion. Therefore, the committee used these capabilities as the required system improvements for the purposes of this study.



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