Programs are in progress to enhance the producibility and maintainability/operability of the high speed turbomachinery required for reusable high-performance engines. For example, the producibility of the alternate high-pressure LOX and hydrogen turbopumps of the SSME Block II engine has been improved substantially through development of nonmetallic bearing balls, integral turbine tip seals, precision castings, and single crystal turbine blades. Precision castings have eliminated the sheet metal housings, which required many welds, in the SSME Phase II engine turbopump designs, thus reducing the need for tedious crack inspections and crack weld repairs during fabrication. The LOX pump is already in use and should be easily available for X-33. The fuel pump is still being tested, but it should also be ready in ample time for X-33. The increased weight of these pumps can be a great drawback, however.

Improved turbomachinery is vital to the RLV. In this context, improved means reducing weight substantially while maintaining or exceeding the reusability demonstrated by the Block II SSME turbopumps. If Block II pumps live up to expectations, they will approach the minimum reusability requirements for the RLV. Engine F/W is critical to the SSTO, and engine weight is particularly important because of the aft location. Applicability of the best available jet engine technology and experience must be emphasized. This may be expensive, but payoffs will be high.

All of the engine manufacturers, in cooperation with NASA, are evaluating advanced turbopumps for future engines. The current programs are applicable to new engine concepts in the 400,000-lb-thrust class, such as the Aerospike, the RL-400, and RS2100. Although the approaches differ in detail, all advanced concepts involve reducing the number of parts, using hydrostatic bearings, investigating advanced manufacturing approaches, and utilizing new materials. The record of the SSME pumps clearly indicates that this is a fruitful area for improvement. Development of advanced concepts is essential to achieving the ultimate goal of a highly operable vehicle. Advanced turbopumps incorporating new materials and substantially fewer parts, as exemplified by the RRTT concept, will greatly reduce required maintenance and enhance operability by reducing failure modes and eliminating currently required inspections.

This technology is fairly mature but has not been used in rocket engine turbopumps, although some tests were conducted in connection with the alternate SSME pumps. Hydrostatic bearings are being considered for use in the RRTT and other advanced turbopump designs. These bearings may eliminate many of the failure modes that are a major source of problems in current engines and make designing long-lived