A wide variety of reusable launch vehicle concepts for placing various payloads into low earth orbit are currently being evaluated for potential civil, commercial and military applications. This recent interest is being driven by a desire to achieve reduced payload launch costs and, in some cases, very rapid response capability. In most of these cases, the general requirements of the main propulsion system are similar: a high level of operational availability with minimal operational support activity. Consequently, evaluation of traditional expendable rocket engines as candidates for reusable applications has begun, with an emphasis on understanding whether or not a given engine's operating characteristics are inherently more reusable than another. In support of a planned program to demonstrate a low cost, rapid response reusable launch vehicle, several existing rocket engines were evaluated for feasibility to meet the requirements of a sub-scale reusable launch vehicle demonstrator. Critical propulsion characteristics were defined based on the demonstration objectives of the overall program. Potential candidate engines were selected and then evaluated against these critical propulsion characteristics, and a comparative assessment of each engine's ability to satisfy each critical characteristic was generated. Finally, a reference engine was designated along with a reference demonstrator vehicle concept. This vehicle concept was evaluated for its feasibility to satisty the reusable launch vehicle demonstrator program objectives, and determined to meet the stated goals with residual capability for possible later applications.

The key to opening the use of space to private enterprise and to broader public uses lies in reducing the cost of the transportation to space. More routine, affordable access to space will entail aircraft-like quick turnaround and reliable operations. Currently, the space Shuttle is the only reusable launch vehicle, and even parts of it are expendable while other parts require frequent and extensive refurbishment. NASA's highest priority new activity, the Reusable Launch Vehicle program, is directed toward developing technologies to enable a new generation of space launchers, perhaps but not necessarily with single stage to orbit capability. This book assesses whether the technology development, test and analysis programs in propulsion and materials-related technologies are properly constituted to provide the information required to support a December 1996 decision to build the X-33, a technology demonstrator vehicle; and suggest, as appropriate, necessary changes in these programs to ensure that they will support vehicle feasibility goals.

Rocket and air-breathing propulsion systems are the foundation on which planning for future aerospace systems rests. A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs assesses the existing technical base in these areas and examines the future Air Force capabilities the base will be expected to support. This report also defines gaps and recommends where future warfighter capabilities not yet fully defined could be met by current science and technology development plans.