Challenges, Enabling Technologies and Technology Maturity for Responsive Space Dr. Kevin G. Bowcutt S. Jason Hatakeyama Boeing Phantom Works, Huntington Beach, CA AIAA 2nd Responsive Space Conference 21 April, 2004

Introduction Over the past 20 years there have been numerous attempts to develop a new RLV All failed or prematurely canceled All share a common issue: lack of technology maturity of fundamental components to meet needs of RLV safety, reliability, affordability and responsiveness Focusing only on the truly enabling RLV technologies in a national effort should help break this cycle Identify enabling technologies, assess their readiness, create detailed tech development roadmaps, and create a national program with sufficient will and resources for success Limited maturity and analysis uncertainty of highly reusable, rapid turnaround, low cost rocket and air-breathing engines make optimal RLV propulsion choice unclear Employ a JSF-like fly-off of both engine types to gather data needed to decide which approach best meets RLV user needs

Propulsion System Fly-Off Model Joint Advanced Strike Technology (JAST) program established in 1994 to create “building blocks for affordable development of the next-generation strike weapon system” Joint Strike Fighter (JSF) program then pitted X-32 direct lift propulsion against X-35 shaft-driven lift fan Analysis-based performance, turnaround time and cost projections contain insufficient data and fidelity to support conclusions about rocket vs. air-breathing RLV choice Develop both engines sufficient for flight test and to enable evaluation of performance, turnaround time and cost metrics Conduct JSF-like fly-off between RLV boosters to gather data necessary to make concrete concept selection decision Minimize flight development cost, but retain sufficient booster performance to gather needed decision data and to yield an initial RLV spiral for global strike and/or responsive spacelift

Rocket vs. Air-Breathing Turbine RLV Booster Reusable hydrocarbon or LH2 rocket booster stage Expendable upper stages Reusable Mach ~ 4 turbine or Mach 4 turbine + Mach 6 ramjet booster stage Expendable upper stages Next RLV spiral could replace expendable 2nd stage with a reusable rocket stage, or perhaps a reusable scramjet or RBCC powered 2nd stage if air-breathing option wins fly-off Other vehicle classes could be developed from mature tech base Key to rapid system development is integrated vehicle design and MDO

Mach 4+ Turbine Accelerator Engine Can Be Developed to Meet RLV Requirements Given SR-71 & XB-70 experience, Mach 4 turbine a largely evolutionary advancement Principal challenges for RLV applications: high thrust-to-weight ratio, thermal management, airframe integration, increased reliability and service life NASA Revolutionary Turbine Accelerator (RTA) program developing mid-scale Mach 4+ turbine that could be used for RLV fly-off Program at risk given President’s new space exploration initiative

Isp & T/W Conflict With Operability Rocket Engine Design Goal Interactions Hamper Ability to Meet Performance, Operability and Cost Objectives Isp & T/W Conflict With Operability Engines have been designed separately for goals of performance, cost and operability, but the challenge of achieving all three objectives concurrently remains formidable Rocket high energy-density, low operational time and few design generations make design to meet all RLV objectives challenging

Space Shuttle Main Engine Designed for High Performance Cycle Propellants FRSC LOX/LH2 Thrust in Vacuum 512, 950 lb Thrust at Sea Level 418,660 lb Isp in vacuum(s) 452 sec Mixture Ratio 6.0:1 Dry Weight 7,480 lb Chamber Pressure 3,008 psia Nozzle Area Ratio 69:1 http://www.boeing.com/defense-space/space/propul/SSME.html

Delta IV RS-68 Designed for Low Cost Propellants LOX/LH2 Thrust in Vacuum 745,000 lb Thrust at Sea Level 650,000 lb Isp in vacuum(s) 410 sec Isp at sea level 365 sec Mixture Ratio 6.0:1 Dry Weight 14,560 lb Chamber Pressure 1,410 psia Nozzle Area Ratio 21.5:1 http://www.boeing.com/defense-space/space/propul/RS68.html

NGLT RS-84 Prototype Designed for Operability ORSC cycle Lox/RP-1 Single ox-rich pre-burner Parallel turbine drive 1,050 klbf prototype Design at PDR (June ’03) Optimized for safety & reliability

No Existing Engine Meets Cost & Operability Goals NGLT Program Had Embarked on Operable Engine Demos Major rapid turnaround technologies: Rapid drying & purge Leak-proof systems Automated health management systems with limited visual inspections Non-pyrotechnic ignition systems Key challenge is technology integration and system design

Hypersonic Air-Breathing RLV Example of Proposed Technology Maturation Process Four technologies deemed critical and enabling for a hypersonic air-breathing RLV (Boeing Technical Fellowship Advisory Board Study, 2003) Air-breathing propulsion High-temperature materials & thermal protection systems (TPS) Reusable cryogenic tanks and integrated airframe structures Integrated vehicle design and multidisciplinary design optimization 3 of 4 enabling technologies common to rocket and air-breathing RLVs All should be matured to a TRL = 6-7 before embarking on RLV development (same holds true for reusable rocket propulsion)

Scramjet Propulsion and TPS Technology Readiness Level Assessment

Cryogenic Tanks, Structures and Vehicle Design Technology Readiness Level Assessment

Notional Enabling Technology Roadmap

Notional Hypersonic Air-Breathing Propulsion Technology Roadmap

Summary Over the past 20 years there have been numerous attempts to develop a new RLV, but none have succeeded due in part to lack of maturity of enabling technologies Focusing only on the truly enabling RLV technologies in a national effort should help break this cycle Rocket and air-breathing turbine engines both require similar time, money and risk reduction to concurrently achieve RLV performance, cost and operability objectives Existing uncertainties make best choice for RLV unclear A JSF-like fly-off of both rocket and air-breathing RLV boosters could be used to determine approach that provides best capabilities for Operationally Responsive Space