The committee believes that responsiveness should be a major consideration when developing reusable launch systems and their supporting technologies. At the present time, no responsiveness requirements beyond a launch-on-schedule philosophy have been defined. Since these requirements can drive vehicle and technology needs, it is imperative that the Air Force define nominal responsiveness goals to provide a focus for research and development activities.

Recommendation 2: Independent of any decision to proceed with RBS development, the Air Force should proceed with technology development in the following key areas: reusable oxygen-rich, staged-combustion hydrocarbon-fueled engines; rocketback return-to-launch-site operations; vehicle health management systems; and adaptive guidance and control systems. These technologies will have to be matured before they can support any future decision on RBS, and most of them will be also applicable to alternative launch system concepts.

Continued development is needed in these four technology areas so they can be matured to the point where significant investments can be committed to the RBS programs. Investments in the four areas should continue independent of a decision to proceed with RBS development. Since the technologies have application beyond RBS, with the exception of rocketback RTLS, their maturation will benefit the Air Force independent of RBS in advanced rocket propulsion, system reliability, and vehicle autonomy.

Recommendation 3: The Air Force Research Laboratory’s (AFRL’s) Pathfinder project is under way to demonstrate in flight, using a small-scale vehicle, the critical aspects of the return-to-launch-site maneuver. To increase chances for Pathfinder’s success, AFRL should develop and fly more than one Pathfinder test vehicle design. In addition, competition among RBS concepts should be maintained as long as possible to obtain the best system for the next generation of space launch.

The use of a rocketback maneuver for RTLS operations of an RBS has not yet been demonstrated, so this approach to reusability carries significant risk. Given these risks and the resulting parameter space for innovative solutions, the Pathfinder program should be executed in a manner wherein several vehicle designs are developed and flown. While this approach will increase costs in the near term, the long-term benefits of one day achieving a true high-performance solution to reusability will overwhelm this initial cost.

Recommendation 4: The decision to proceed with the RBS development program should be based on the successful completion of the Pathfinder activities and on assurance that the technical risks associated with the reusable oxygen-rich, staged-combustion hydrocarbon-fueled engines, rocketback return-to-launch-site, vehicle health management systems, and adaptive guidance and control systems are adequately mitigated.

Given the immaturity of the principal technologies and the inherent risks of the rocketback RTLS operation, the decision to proceed with RBS development should be tied to the successful completion of the Pathfinder program and suitable mitigation of the principal technical risks. The committee understands that this approach will delay the achievement of an RBS capability. However, delaying the decision to proceed with the RBS development has an additional benefit: It enables the business environment for emerging new-entrant commercial launch providers to become clearer.

Recommendation 5: Following successful completion of the Pathfinder program, the Air Force should reevaluate the RBS business case, accounting for the following factors: new-entrant commercial launch providers; potential impacts of single-source providers; and Air Force need for independent launchers to satisfy assured-access-to-space requirements.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement