A Collaborative Effort for Manufacturing and Testing of GEM Rocket Propellant

1. A Collaborative Effort for Manufacturing and Testing of GEM Rocket Propellant Presented by: Mike Rose, Connie Murphy and Rich Muscato

2. Outline • Program objectives • NSWC-IH Accomplishments • Process transition • Computer modeling • Inert processing • Live processing • Ballistic differences • Motor Firings • Conclusions

3. Program Objectives • NSWC-IH • Develop a continuous manufacturing process for TPE based rocket propellant using a twin screw extruder (TSE) • Manufacture TPE based rocket propellant in the 40mm TSE and test • Establish baseline ballistic data (strands) based on specific ballistic targets for burn rate and slope • Provide propellant for high pressure motor firings • Transfer process technology to ATK Thiokol for scale-up work • ATK Thiokol • Scale-up continuous manufacturing process established at NSWC-IH to 58mm TSE • Manufacture TPE based rocket propellant in the 58mm and test • Compare ballistic data to NSWC-IH baseline targeting burn rate and slope • Recover, recycle, re-use (R3) • Test high pressure motors using propellant manufactured at NSWC-IH and ATK Thiokol

4. NSWC-IH Accomplishments • Developed a continuous manufacturing process for TPE based rocket propellant using a twin screw extruder (TSE) • Characterized raw material feed streams • Flow rates and location • Optimized extrusion process parameters for the 40mm TSE • Temperature profile, screw configuration and screw speed • Successfully and safely manufactured TPE based rocket propellant in the 40mm TSE and established ballistic baseline data • Specific targets for burn rate and slope • Demonstrated consistent propellant properties from run to run • Physical (density) and ballistic (burn rate and slope) properties • Provided propellant for high pressure motor firings • Transferred process technology to ATK Thiokol for scale-up to 58mm TSE

5. Extrusion Protocol for GEM Rocket Propellant 58mm TSE Inert Processing Safety Characterization of Energetic Materials Technology Transfer from NSWC-IH Rheology Characterization Rheological Characterization Performed by NSWC-IH Computer Modeling 58mm TSE Energetic Processing 40mm TSE Parameters Used for Comparison

6. TSE Computer Modeling Program • Developed by the University of Akron • Modeling program uses finite element analysis to predict one-dimensional fluid flow behavior in a TSE • Program inputs • Barrel and screw configuration • Temperature profile of the extruder barrel • Feed stream flow rates and locations • Screw speed (rpm) • Material properties (physical and rheological) • Program outputs • Profiles along the barrel for: • Pressure, temperature, torque, fill factor, and melt • Specific energy • Model benefits • Quickly assesses relationships and effects of process parameters

7. Modeling Effort • Objectives for computer modeling • Validate model based on actual extrusion data generated by NSWC-IH for the 40mm TSE • Determine comparable process parameters for the 58mm TSE based on 40mm experience • Screw configuration, screw speed, temperature profile and feed stream flow rates • Modeling results • Generated a computer model for the 40mm TSE process that predicted: • Pressure, temperature, fill-factor, and melt profiles along the barrel • Specific energy • Used 40mm data (modeled and actual) to establish a similar model for the 58mm TSE • Established initial process parameters for the 58mm TSE • The computer model did not predict any major concerns

8. Inert Evaluation • Inert runs were used to identify critical issues regarding the entire process and to solidify processing parameters for live efforts • Initial inert run used a substitute for TPE • No unusual temperature excursions were experienced during operation • Torque values were higher than expected • Modified screw configuration to reduce power consumption • Post extrusion examination of the initial inert run identified foiling of the aluminum near the feed inlet of the extruder • NSWC-IH experienced foiling in the solid feeder • Feed screws were changed solving the problem • Cause for the foiling has been attributed to frictional heating • TPE substitute did not coat aluminum quickly enough • Subsequent runs using actual TPE showed no foiling

9. Foiling Buildup in the Barrel Aluminum Flakes in the Material Foiling Removed from the Barrel Foiling Buildup in the Barrel Foiling Buildup in the Barrel Foiling on Screw Element Foiling Phenomenon

10. Initial Live Extrusion • Initial live extrusion runs on the 58mm TSE provided valuable information • Process parameters modified slightly • Screw speed and feed stream flow rates lowered • Identified inherent concerns for the system • Higher than usual humidity caused AP to hang-up in the feed funnel altering the formulation • Provided extrudate for evaluation • Established baseline ballistic properties for 58mm TSE material • Comparison of ballistic properties from extrudate generated from the 40mm and 58mm TSE showed distinct differences in burn rates

11. Ballistic Comparison

12. Evaluation of Burn Rate Differences • Several factors potentially contributed to ballistic differences of the propellant • Raw materials • The same raw materials used in the 40mm TSE • Porosity • Pressed densities generally approached the theoretical maximum density (TMD) of the formulation • Re-processed extrudate in batch mixer and measured burn rates • Formulation differences • Compositional differences could not be determined due to analysis variability • Detailed feed stream analysis performed to minimize variability • Scale-up idiosyncrasies

13. Ballistic Comparison

14. Evaluation of Burn Rate Differences • Several factors potentially contributed to the ballistic difference • Raw materials • The same raw materials used in the 40mm TSE • Porosity • Pressed densities generally approached the theoretical maximum density (TMD) of the formulation • Re-processed extrudate in batch mixer and measured burn rates • Formulation differences • Compositional differences could not be determined due to analysis variability • Detailed feed stream analysis performed to minimize variability • Scale-up idiosyncrasies

15. Feeder Calibration - AP

16. Feeder Calibration - Al

17. Feeder Calibration – TPEInitial Parameters

18. Feeder Data – TPEAdjusted Parameters

19. Ballistic Comparison

20. Process Scale-up Conclusions • Minor material differences (ballistic properties) indicate subtle scale factors exist for the 40mm and 58mm TSE’s • Shear environment • Heat transfer • Process section differences • Modular barrel vs. monolithic barrel • Exact feed port location • Confident that with additional work material properties could be duplicated

21. Predicted Performance Measured Data High Pressure Motor Firing Pressure (psia) Time (sec)

22. Final Program Conclusions • NSWC-IH successfully transferred process technology to ATK Thiokol • Two different extruders, size and configuration, can produce similar material • Modeling played a key role towards reducing experimental iterations • Inert runs provide invaluable process information but should be interpreted carefully • Other program objectives are nearing completion • Results suggest that successful scale-up can be accomplished