• Reusability. A thorough evaluation of all the factors that make current engines and engine-vehicle interfaces less than efficient for reuse is critically needed. Phases I and II technology and test programs are intended to minimize operational delays and hardware failures for the RLV program. Long life and repeatable performance with minimal inspection will be essential.

• Maintainability/Operability. Engine health monitoring, simplified turnaround procedures, and improved and expedited before- and after-flight procedures are important goals. Several technology programs in Phase I are directed at engine health monitoring and simplifying operational systems.

The committee reviewed the engine technology projects established by the prime vehicle contractors and the engine contractors with the intent of determining whether the approach was adequate to support a decision about whether to proceed with an X-33. The engines that will be used to meet the design criteria for an X-33 may differ substantially from the engines contemplated for an eventual RLV. Because of the lengthy development period required for major modifications of existing or new engines, the contractors and engine companies are developing engines to fulfill the X-33 requirements in the engine-vehicle while pursuing the development of the more-capable products that will be needed for an RLV. Therefore, the committee considered the initiation of programs to meet key long-range RLV engine requirements as well as X-33 engine requirements.

1. The propulsion technology area will be adjusted by August of 1995 to reflect the needs of the X-33 industry partners. Propulsion systems not required by the proposed X-33 or RLV will not be funded by this program.

2. A propulsion concept for the RLV configuration will be selected prior to the Phase II decision which will be required by the preferred RLV configuration.

3. A documented analysis will have been completed prior to the Phase II decision which demonstrates that the selected propulsion subsystems are scaleable to a full-scale RLV and that reuse/operations requirements will be adequately demonstrated by a X-33 vehicle. Estimated requirements for the RLV, which will be supported by this analysis, include a 100 mission life with 20 flights between depot maintenance and a 50 percent reduction in engine inspection time between flights as compared to the shuttle.

4. Results from component work will be documented and provided with the above analysis. Only propulsion technology supporting the X-33 contractors will be pursued within this program.