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The use of premixed, shock-induced combustion in the context of a hypervelocity, airbreathing vehicle requires effective injection and mixing of hydrogen fuel and air on the vehicle forebody. Three dimensional computational simulations of fuel injection and mixing from flush-wall and modified ramp and strut injectors are reported in this study. A well-established code, VULCAN, is used to conduct nonreacting, viscous, turbulent simulations on a flat plate at conditions relevant to a Mach 12 flight vehicle forebody. In comparing results of various fuel injection strategies, it is found that strut injection provides the greatest balance of performance between mixing efficiency and stream thrust potential.

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Lazarus is an unmanned single stage reusable launch vehicle concept utilizing advanced propulsion concepts such as rocket based combined cycle engine (RBCC) and high energy density material (HEDM) propellants. These advanced propulsion elements make the Lazarus launch vehicle both feasible and viable in today's highly competitive market. The Lazarus concept is powered by six rocket based combined cycle engines. These engines are designed to operate with HEDM fuel and liquid oxygen (LOX). During atmospheric flight the LOX is augmented by air traveling through the engines and the resulting propellant mass fractions make single stage to orbit (SSTO) possible. A typical hindrance to SSTO vehicles are the large wings and landing gear necessary for takeoff of a fully fueled vehicle. The Lazarus concept addresses this problem by using a sled to take off horizontally. This sled accelerates the vehicle to over 500 mph using the launch vehicle engines and a propellant cross feed system. This propellant feed system allows the vehicle to accelerate using its own propulsion system without carrying the necessary fuel required while it is attached to the sled. Lazarus is designed to deliver 5,000 lbs of payload to a 100 nmi x 100 nmi x 28.5° orbit due East out of Kennedy Space Center (KSC). This mission design allows for rapid redeployment of small orbital assets with little launch preparation. Lazarus is also designed for a secondary strike mission. The high speed and long range inherent in a SSTO launch vehicle make it an ideal global strike platform. Details of the conceptual design process used for Lazarus are included in this paper. The disciplines used in the design include aerodynamics, configuration, propulsion design, trajectory, mass properties, cost, operations, reliability and safety. Each of these disciplines was computed using a conceptual design tool similar to that used in industry. These disciplines were then combined into an integrated design process and used to minimize the gross weight of the Lazarus design. Nomenclature α = angle-of-attack, ° AFRSI = Advanced Flexible Reusable Surface Insulation CAD = computer aided design CER = cost estimating relationship c L = coefficient of lift DDT&E = design, development, test, & evaluation DoD = Department of Defense DSM = Design Structure Matrix EMA = electro-mechanical actuators

The approach and techniques described herein define an optimization and evaluation approach for a liquid hydrogedliquid oxygen single-stage-to-orbit system. The method uses Monte Carlo simulations, genetic algorithm solvers, a propulsion thermo-chemical code, power series regression curves for historical data, and statistical models in order to optimize a vehicie system. Tie sysbm, inciuding paraleien h r eiigiiie ciiiiiiibei-pi-eSsui-c, area Iatiio, aid oxidizer/fuel ratio, was modeled and optimized to determine the best design for seven separate design weight and cost cases by varying design and technology parameters. Significant model results show that a 53% increase in Design, Development, Test and Evaluation cost results in a 67% reduction in Gross Liftoff Weight. Other key findings show the sensitivity of propulsion parameters, technology factors, and cost factors and how these parameters differ when cost and weight are optimized separately. Each of the three key propulsion parameters; chamber pressure, area ratio, and oxidizer/fuel ratio, are optimized in the seven design cases and results are plotted to show impacts to engine mass and overall vehicle mass.

V, free-stream w l o c l t y z A method for predlctlng t h e performance i~ viscous correlation paraneter, w&/K aerodynamlcs of aeroasslsted Orbltdl t r a n s f e r v d r l c l e s was developed based on technlgues that Space Shuttle o r b l t e r and theorles from the -, mro used I n the .erodynamlC ddtdbook Of the a angle of attack Hvnersonlc h r b l t r a r y Body R w r a m . The method Y rat10 O f SpGCif1C heats ,bans the e n t l r e f l i g h t broflie of the derOaSSisted Orbltdl t r a n s f e r Vehicles from t h e extreme high altltuck non-continwm re ine to the highly viscous continurn regime. Resufts from t h l s llethod me mnpared wlth f l l g h t data from t h e Shuttle orblter. Apollo Capsule. and the Vlklng Aeroshell. Flnally, performance aerodynamics are estimated for three aeroassisted o r b i t a l t r a n s f e r vehlcles t h a t range from low t o hlgh 1Ift-to-drag r a t i o conflguratlons. NOMENCLATUIE CA Chdpmdn-Rubesin vlacoslty coefficient CA a x l a l coefflclent, axlal f0rcelq.S Co drag cuefflcient, drag forceles CL lift coefflclent, l i f t force/eS w c, , normal coefflclent, normal f o r c e / e S S mference area. 4. Tw wall tanperature . . T, free-stream temperature T' reference tcrnperature *Aerospace Englneer, Space System Dlvlslon. Member AIM. *.Head, Vehlcle Analysts Branch, space Systems Dlvlslon. Meknber AIM. A mean free path u , free-stream vlscoslty a energy acconndatlon coefflclent Abbrevlatlons AOTV a e r m s s i s t e d o r b l t a l t r a n s f e r vehlclea FW free molecular flow HAB

The objective of space habitat design is to minimize mass and system size while providing adequate space for all necessary equipment and a functional layout that supports crew health and productivity. Unfortunately, development and evaluation of interior layouts is often ignored during conceptual design because of the subjectivity and long times required using current evaluation methods (e.g., human-in-the-loop mockup tests and in-depth CAD evaluations). Early, more objective assessment could prevent expensive design changes that may increase vehicle mass and compromise functionality. This paper describes a new interior design evaluation method to enable early, structured consideration of habitat interior layouts. This interior layout evaluation method features a comprehensive list of quantifiable habitat layout evaluation criteria, automatic methods to measure these criteria from a geometry model, and application of systems engineering tools and numerical methods to construct a multi-objective value function measuring the overall habitat layout performance. In addition to a detailed description of this method, a C++/OpenGL software tool which has been developed to implement this method is also discussed. This tool leverages geometry modeling coupled with collision detection techniques to identify favorable layouts subject to multiple constraints and objectives (e.g., minimize mass, maximize contiguous habitable volume, maximize task performance, and minimize crew safety risks). Finally, a few habitat layout evaluation examples are described to demonstrate the effectiveness of this method and tool to influence habitat design.