A nonlinear, physics-based model of the longitudinal dynamics for an air-breathing hypersonic vehicle is developed. The model is derived from first principles and captures a number of complex interactions between the propulsion system, aerodynamics, and structural dynamics. Unlike conventional aircraft, air-breathing hypersonic vehicles require that the propulsion system be highly integrated into the airframe. Furthermore, full-scale hypersonic aircraft tend to have very lightweight, flexible structures that have low natural frequencies. Therefore, the first bending mode of the fuselage is important, as its deflection affects the amount of airflow entering the engine, thus influencing the performance of the propulsion system. The equations of motion for the flexible aircraft are derivedusingLagrange’sequations.Theequationsof motioncaptureinertial couplingeffectsbetween thepitch and normal accelerations of the aircraft and the structural dynamics. The linearized aircraft dynamics are found to be unstableand,inmostcases,exhibitnonminimumphasebehavior.Thelinearizedmodelalsoindicatesthatthereisan aeroelastic mode that has a natural frequency more than twice the frequency of the fuselage bending mode, and the short-period mode is very strongly coupled with the bending mode of the fuselage.

Nonlinear Longitudinal Dynamical Model of an Air-Breathing Hypersonic Vehicle

: A non-linear, physics-based model of the longitudinal dynamics for an air-breathing hypersonic vehicle is developed. The model is derived from first principles and captures the complex interactions between the propulsion system, aerodynamics, and structural dynamics. Unlike conventional aircraft, hypersonic vehicles require that the propulsion system be highly integrated into the airframe. Furthermore, hypersonic aircraft tend to have very lightweight, flexible structures that have low natural frequencies. Therefore, the first bending mode of the fuselage is important as its deflection affects the amount of airflow entering the engine, thus influencing the performance of the propulsion system. The equations of motion for the flexible aircraft are derived using Lagrange's Equations. The equations-of-motion capture inertial coupling effects between the pitch and normal accelerations of the aircraft and the structural dynamics. The linearized aircraft dynamics are shown to be unstable, and in most cases, exhibit non-minimum, phase behavior. The linearized model also indicates that there is an aeroelastic mode that has a natural frequency more than twice the frequency of the fuselage bending mode. Furthermore, the short-period mode is very strongly coupled with the bending mode of the fuselage.

A Non-Linear Model for the Longitudinal Dynamics of a Hypersonic Air-breathing Vehicle

A review of rocket-airbreathing combined-cycle propulsion systems for Earth-to-orbit applications is presented. Rocket-based combined-cycle (RBCC) engines take advantage of the synergistic interactions between the rocket and the airbreathing elements of the engine and the use of high-specie c impulse cycles to yield a mission-averaged specie c impulse that is higher than all-rocket technology can provide. An overview of the multimode operation is given, along with a review of both experimental and modeling work that has been done on this class of engines. Selected issues involved with these engines are discussed. These include engine/vehicle integration, e ow-path design for multimode operation, fuel selection, mixing enhancement and afterburning in rocket-ejector mode, thermal choking, and e ameholding. RBCC propulsion is becoming recognized as a promising technology for achieving a signie cant reduction in the cost of delivering payload to orbit.

Combined Rocket and Airbreathing Propulsion Systems for Space-Launch Applications

Operating conditions and performances of a fixed-geometry combined-cycle engine for a single-stage-to-orbit aerospace plane were calculated with a simple simulation model. With the flow conditions calculated with the model, the cooling requirement of the engine and pitching moment of the plane were investigated. The engine was composed of an ejector-jet mode, a ramjet mode, a scramjet mode, and a rocket mode. The engine had a fixed geometry in its operation. Subsonic combustion was conducted with no second throat in the combustor under the ejector-jet mode and the ramjet mode. Propellants were liquid hydrogen and liquid oxygen. The coolant flow rate became larger than the fuel flow rate. The excessive flow rate decreased the specific impulse above Mach 9 and restricted application of the airbreathing engine mode up to Mach 11. The pitching moment of the plane would be balanced even in the space in the configuration with the combined-cycle engine mounted on the windward surface.

Conceptual Study of a Combined-Cycle Engine for an Aerospace Plane

Micromanufacturing technologies of compact heat exchangers for hypersonic precooled airbreathing propulsion: A review

A new computer analysis tool capable of predicting rocket-based combined-cycle engine performance data (thrust and Isp) over a wide range of e ight conditions and engine operating modes is presented. The tool is called SCCREAM, which stands for simulated combined-cycle rocket engine analysis module. SCCREAM is an objectorientedworkstation-levelcodewritteninC++thatcanberemotelyexecutedthroughaweb-baseduserinterface.It uses quasi-one-dimensional e ow analysis techniques, componentand combustion efe ciencies, and an inlet pressure recovery schedule as simplifying assumptions. SCCREAM was created for the conceptual launch vehicle design environment and is capable of quickly generating large tables of engine performance data for use in subsequent trajectory optimization. An overview of SCCREAM and the program logic is presented. Results from SCCREAM are compared with published rocket-based combined-cycle engine performance data and with data generated by other engine analysis tools for a representative reference vehicle cone guration.

SCCREAM: A Conceptual Rocket-Based Combined-Cycle Engine Performance Analysis Tool

Rocket-based combined-cycle engines are currently under consideration for use on future, reusable launch vehicles. By combining traditional rocket and airbreathing operating modes into a single engine, multi-mode RBCC engines offer a number of advantages for launch vehicle designers including higher trajectory averaged L^, than pure rockets and higher installed thrust-to-weight ratios than pure airbreathers. This paper presents a new computer tool capable of predicting RBCC engine performance (thrust and 1^) over a wide range of flight conditions and engine operating modes. The tool is called SCCREAM — Simulated Combined-Cycle Rocket Engine Analysis Module. SCCREAM is an object-oriented workstation-level code written in C++. It uses quasi1D flow analysis, component and combustion efficiencies, and an inlet pressure recovery schedule as simplifying assumptions. SCCREAM was created for the conceptual launch vehicle design environment and is capable of quickly generating large tables of engine performance data for use in trajectory optimization. An overview of SCCREAM and the program logic is presented. Results from SCCREAM are favorably compared to historical RBCC engine performance data and to data generated by other engine design tools.

SCCREAM (Simulated Combined-Cycle Rocket Engine Analysis Module): A Conceptual RBCC Engine Design Tool

9th International Space Planes and Hypersonic Systems and Technologies Conference
Norfolk, VA, November 1-5, 1999.

Hyperion: An SSTO Vision Vehicle Concept Utilizing Rocket-Based Combined Cycle Propulsion

The Rocket Engine Design Tool for Optimal Performance-2 (REDTOP-2) is a newly created engineering design tool for use in the conc eptual and preliminary design of space transportation systems utilizing liquid propulsion rocket engines. REDTOP-2, one of many unique engineering tools commercially available from SpaceWorks Engineering, Inc. (SEI), represents a novel entry into the current suite of propulsion modeling tools. REDTOP-2 is capable of analyzing the flowpath characteristics of numerous engine configurations to perform a power balance of the turbomachinery hardware (pumps and turbines) to achieve a user specified main chamber combustion pressure. The engine performance, in terms of thrust and specific impulse (Isp), is then determin ed based on the results of this power balance and the flow conditions (pressure, temperat ure, flowrate, etc.) in the chamber(s) and nozzle(s). Engine weight is assessed at the main co mponent level using a combination of empirical and physics based analysis methods to provide vacuum, ambient, and sea-level thrust-to-weight (T/W) values. A cost model capable of predicting engine development, first unit, and production costs has been incorporated. Additionally, REDTOP-2 features a topdown modeling approach for computing engine safety and reliability metrics. REDTOP-2 is written in the modern, object-oriented C++ programming language and will execute on PC, Mac, and SGI platforms. Execution times are on the order of 30 seconds to 5 minutes, depending on the computing platform, engine configuration and design option selected by the user. User interface options currently include a command-line execution with ASCII file manipulation, filewrappers for use in Phoenix Integ ration’s ModelCenter© environment, and a PC-based graphical user interface (GUI). This paper will describe the REDTOP-2 tool and its capabilities. Sample results obtained from exercising the tool for a number of different existing engine designs will be presented . Results from a multi-variable sensitivity study on a LOX/LH2 fuel-rich, single preburner staged-combustion engine will be highlighted. Two sample applications involving vehi cle designs will be discussed. The first involves probabilistic/uncertainty analysis for an all-rocket vehicle design and the second the rocket main propulsion system analysis of an airbre athing, two-stage RLV concept with first stage tail-rockets and all-rocket second stage prop ulsion. Finally, future directions in the development of REDTOP-2 will be discussed.

http://www.sei.aero/eng/papers/uploads/archive/AIAA-2004-3514.pdf

REDTOP-2: Rocket Engine Design Tool Featuring Engine Performance, Weight, Cost, and Reliability

In order to counter newly emerging threats and offensive posturing from hostile countries, the United States military has identified responsive space access as a necessary capability to provide security and defense for the nation. An option for enabling quick, ondemand space access involves reusable transportation elements. Specifically, elements that incorporate air-breathing propulsion systems to provide multi-role mission capabilities, loiter capability, flyout, and abort options. These capabilities are not generally possible on systems that only utilize rocket propulsion systems. In support of this vision, the Air Force Research Lab has initiated concept development studies in the area of combined-cycle propulsion systems applied to reusable launch vehicles. The first product from this study has resulted in the design of a space operations vehicle (SOV) referred to as the Quicksat. This SOV is the first element of a two-stage launch vehicle concept that uses combined-cycle airbreathing propulsion. The nominal system launches and lands horizontally in addition to using non-cryogenic propellants for improved operability in support of on-demand and responsive launch scenarios. Additionally, the unique vehicle is capable of supporting at least three unique missions: a) space maneuvering vehicle (SMV) delivery to orbit, b) a hypersonic strike mission, and c) cargo delivery to LEO and polar orbits.

John Edward Bradford

Papers

SCCREAM: A Conceptual Rocket-Based Combined-Cycle Engine Performance Analysis Tool

SCCREAM (Simulated Combined-Cycle Rocket Engine Analysis Module): A Conceptual RBCC Engine Design Tool

Hyperion: An SSTO Vision Vehicle Concept Utilizing Rocket-Based Combined Cycle Propulsion

REDTOP-2: Rocket Engine Design Tool Featuring Engine Performance, Weight, Cost, and Reliability

Quicksat : A Two-Stage to Orbit Reusable Launch Vehicle Utilizing Air-Breathing Propulsion for Responsive Space Access