An Evaluation of Two Alternate Propulsion Concepts for Bantam-Argus: Deeply-Cooled Turbojet+Rocket and Pulsed Detonation Rocket+Ramjet
The Bantam-Argus reusable launch vehicle concept is a smaller version of the original Argus single-stage-to-orbit launch vehicle design. Like the original Argus, Bantam-Argus uses a Maglifter launch assist system to provide an initial horizontal launch velocity. Bantam-Argus is designed to deliver 300 lb. payloads to low earth orbit and, like the full sized Argus, the baseline Bantam-Argus concept utilizes two liquid oxygen/liquid hydrogen supercharged ejector ramjets as prime motive power. This paper presents the results of an investigation of two alternate propulsion systems for the BantamArgus launch vehicle. First, a thermally integrated combined-cycle system consisting of two deeplycooled turbojets and two liquid rocket engines was evaluated. Second, a combination propulsion system utilizing two pulsed detonation rocket engines and two standalone ramjets was evaluated. The results show that both alternate propulsion systems have the potential to reduce both the dry weight and gross weight of the baseline Bantam-Argus concept (when resizing the vehicle while holding mission payload constant). The pulsed detonation rocket engine option is particularly attractive. However, these results must be treated with caution given the relative immaturity of the supporting propulsion data available for both alternatives. Trade studies on key performance parameters were p rformed to bound the potential gains to be expected from either alternative.
Component-Level Weight Analysis for RBCC Engines
Rocket-based combined-cycle (RBCC) engines have recently received increased attention for use on advanced, reusable space launch vehicles. By combining conventional rocket and airbreathing operating modes into an integrated unit, they have given designers a middle ground between the highthrust, low-Isp characteristics of a pure rocket and the low-thrust, high-Isp of pure airbreathers. Engine weight (or thrust-to-weight ratio) is a highly sensitive parameter in the design of advanced reusable launch vehicles. While substantial experience exists with ground-test engines from the 1960's, little parametric data exists to help conceptual designers predict weight for today's advanced technology, flight-weight RBCC engines. This paper reports a new set of component-level parametric weight estimating equations for advanced RBCC engines. These equations are derived from topdown regression analysis of historical data and include variables to account for advanced technologies and materials. Component weight equations are given as functions of engine geometry, internal pressure, flight modes, etc. Taken together, the equations are used to build up an overall RBCC weight estimation model — WATES. This spreadsheet-based model is not intended to replace a more detailed weight analysis, but rather to assist conceptual vehicle designers in assessing the relative advantages of various engine concepts. Sample RBCC engine weight predictions are given. ' Assistant Professor, School of Aerospace Engineering, senior member AIAA. f Graduate Research Assistant, School of Aerospace Engineering, student member AIAA. Copyright © 1997 by John R. Olds and David J. McCormick. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. NOMENCLATURE Ac inlet or cowl frontal area (sq. inches) Cf complexity factor for variable geometry ERJ ejector ramjet ESJ ejector scramjet ISP specific impulse (sec.) L/D length-to-diameter ratio LH2 liquid hydrogen LOX liquid oxygen M,mns transition Mach number to rocket mode MDC Mixer-Diffuser-Combustor Pint internal static design pressure (psia) PR fan (total) pressure ratio RBCC Rocket-Based Combined-Cycle SERJ supercharged ejector ramjet SESJ supercharged ejector scramjet SLS sea-level static (takeoff condition) T/W thrust-to-weight ratio TAD Technology Availability Date TRF Technology Reduction Factor V internal volume of MDC (cubic inches) WATES Weight Assessment Tool for Engine Scaling WBS Weight Breakdown Structure WER Weight Estimating Rlationship Wp rocket primary weight flow rate (Ib/s) Ws secondary or inlet weight flow rate (Ib/s) Wtota! total or nozzle weight flow rate (Ib/s)
Results of a Rocket-Based Combined-Cycle SSTO Design Using Parametric; MDO Methods
This paper reports the results of the second phase of a research project to characterize and optimize the design of an advanced launch vehicle for human access to low earth orbit. The vehicle makes use of rocket-based combined-cycle (RBCC) propulsion — a concept combining operating modes of an ejector, ramjet, scramjet, and rocket in a single engine. This research builds on previous work focused on advanced multiple mode propulsion concepts and advanced conical acceleration-class single-stage-toorbit (SSTO) launch vehicles. Three systems level design variables of interest were optimized using multidisciplinary design optimization (MDO) techniques. Specifically, Taguchi’s method of robust design was used to identify a combination of variables that minimize the vehicle sensitivity to unpredictable changes in engine weights and performance. In addition, a second-order response surface method (RSM) was used to approximate the design space and predict the minimum dry weight vehicle. The optimized vehicle results (weights, dimensions, performance) are favorably compared with other SSTO designs including rocket and airbreathing concepts.