Concept Assessment of a Hydrocarbon Fueled Rbcc-powered Military Spaceplane

The U.S. Air Force has long been interested in the next-generation space launch capabilities that might be enabled by high-speed air-breathing propulsion. Since the early 1960's, studies have examined the application of ramjet or dual-mode scramjet propulsion to potential reusable military spaceplane (MSP) concepts. Perceived advantages include flexible basing, flexible operations, hypersonic strike from the Continental U.S., and low cost space access. However, many of the requisite propulsion technologies for high-speed air-breathing flight remain ongoing research efforts still today. Vehicle studies and concept assessments are typically used to provide a guiding vision to propulsion research efforts. These studies help define requirements and goals while also serving to explore the potential advantages and disadvantages of air-breathing space launch vehicles relative to current alternatives. The paper will highlight one of the advanced vehicle concepts developed under a project entitled "Innovative Concept Development of Reusable Launch Vehicles Using Combined-Cycle Propulsion for Military Applications." SpaceWorks Engineering, Inc. (SEI) conducted the project under a multi-year award from the Air Force Research Laboratory's Propulsion Directorate, Wright-Patterson AFB, OH . The concept to be reported on is a two-stage, vertical takeoff/horizontal landing MSP concept referred to as the Sentinel. This vehicle uses RBCC engines as the primary propulsion system for the reusable booster stage. The booster is capable of supporting three different missions by configuring the expendable upperstage with missionspecific hardware. These missions include: a) space maneuvering vehicle (SMV) delivery to orbit, b) a hypersonic strike mission, and c) cargo delivery to due-East low Earth orbit (LEO) from Cape Canaveral Air Force Station (CCAFS) as well as polar orbits from Vandenberg Air Force Base (VAFB). Several trade studies were conducted on the Sentinel concept. Various flyback conditions, the sensitivity to installed engine weight, and different missions were each evaluated. These trade study results as well as the baseline configuration results will be reported along with summary conclusions in this paper. Results of the cost, safety/reliability, and operations assessment for the Sentinel will not be presented in this paper.