0. 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

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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)

11. Scramjet Propulsion and TPS Technology Readiness Level Assessment

12. Cryogenic Tanks, Structures and Vehicle Design Technology Readiness Level Assessment

13. Notional Enabling Technology Roadmap

14. Notional Hypersonic Air-Breathing Propulsion Technology Roadmap

15. 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