AIAA 96-2688 Options for Flight Testing Rocket-Based Combined-Cycle (RBCC) Engines

While NASA’s current next-generation launch vehicle research has largely focused on advanced allrocket single-stage-to-orbit vehicles (i.e. the X-33 and it’s RLV operational follow-on), some attention is being given to advanced propulsion concepts suitable for “next-generation-and-a-half” vehicles. Rocketbased combined-cycle (RBCC) engines combining rocket and airbreathing elements are one candidate concept. Preliminary RBCC engine development was undertaken by the United States in the 1960’s. However, additional ground and flight research is required to bring the engine to technological maturity. This paper presents two options for flight testing early versions of the RBCC ejector scramjet engine. The first option mounts a single RBCC engine module to the X-34 air-launched technology testbed for test flights up to about Mach 6.4. The second option links RBCC engine testing to the simultaneous development of a small-payload (220 lb.) two-stage-to-orbit operational vehicle in the Bantam payload class. This launcher/testbed concept has been dubbed the W vehicle. The W vehicle can also serve as an early ejector ramjet RBCC launcher (albeit at a lower payload). To complement current RBCC ground testing efforts, both flight test engines will use earth-storable propellants for their RBCC rocket primaries and hydrocarbon fuel for their airbreathing modes. Performance and vehicle sizing results are presented for both options. NOMENCLATURE Ac engine capture area (ft ) APAS Aerodynamic Preliminary Analysis System Ct thrust coefficient (thrust/q*Ac) Cd aerodynamic drag coefficient ERJ ejector ramjet RBCC engine ESJ ejector scramjet RBCC engine GASL General Applied Science Laboratory H2O2 hydrogen peroxide HRE hypersonic research engine IRFNA inhibited red fuming nitric acid (G = gelled) Isp specific impulse (seconds) I* rocket equation effective Isp (seconds) JP jet fuel (one of several hydrocarbon variants) LACE liquid air cycle engine LaRC NASA Langley Research Center LEO low earth orbit (typically < 250 nmi.) LeRC NASA Lewis Research Center LH2 liquid hydrogen LOX liquid oxygen M flight Mach number MER mass estimating relationship MMH monomethyl hydrazine (G = gelled) MR mass ratio (initial weight/burnout weight) MSFC NASA Marshall Space Flight Center OSC Orbital Sciences Corporation POST Program to Optimize Simulated Trajectories q dynamic pressure (ρV/2, lb/ft) RBCC rocket-based combined-cycle RLV reusable launch vehicle RP1 rocket propellant (hydrocarbon) SLS sea-level static SSTO single-stage-to-orbit T engine thrust (lb.) T/W engine thrust-to-weight ratio TPS thermal protection system TSTO two-stage-to-orbit ∆V velocity change (feet/second) _________________________ † Assistant Professor, School of Aerospace Engineering, Member AIAA. Copyright © 1996 by John R. Olds. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission.