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Low Cost, High Performance, Elastomeric Case Insulation for Solid Rocket Motors

Description:

 
 

TECHNOLOGY AREA(S): Materials/Processes

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 5.4.c.(8) of the solicitation.

OBJECTIVE: Develop a low cost, domestically sustainable, elastomeric material for use as internal solid rocket motor case insulation, and demonstrate improved performance over state-of-the-art materials through increased stable char yield, reduced erosion, and low thermal conductivity of material up to maximum internal case temperatures.

DESCRIPTION: Traditional solid rocket motors require internal case insulation to prevent overheating of the motor case and subsequent failure of the motor. As newer designs utilizing composite materials begin to replace metal rocket motor cases to provide improved structural and Insensitive Munitions (IM) performance, internal insulation remains critical to keep the case wall well below the glass transition temperature of the matrix. Another essential function of the insulator when used in composite motor cases is to serve as the pressure seal. In addition to providing the necessary insulation for the motor case wall, these materials can also be tailored for use in thermal barriers, supporting multi-mission and extended range goals for tactical missiles.

Conventional motor case insulation materials are easily eroded when confronted with high heat flux and particle impingement. While some of this material ablation contributes to heat removal, increased insulation thickness is required to account for the material loss and maintain a positive thermal margin at the case wall. As a result, the thicker insulation consumes critical volume within the rocket motor and adds unwanted mass.

The intent of this topic is to develop novel, improved performance insulation materials through the use of commercially available constituent materials (additives, modifiers, fillers, reinforcements, etc.) that enable the production of a thick, tenacious, low thermal conductivity char. Balance between heat removal via mass loss and char stability is desired.

A focus on low cost materials and processes is essential, as is the long term domestic viability of the new material. Processability of the new material is critical for ease of insertion into typical solid rocket motor case manufacturing processes. In addition, special consideration must be given to the interface of the insulation material with the propellant. The insulator must have stable properties across the operating temperature range of the missile (typically -45 °F to +145 °F).

PHASE I: Identify and evaluate candidate materials to satisfy the performance objectives: thermal conductivity of the virgin material < 0.21 BTU/hr-ft-°F, and thermal conductivity of the charred material < 126.0 (BTU/ft-sec-°R) x 10^-6 at 6460 °R. Develop processing methods to ensure and demonstrate scalable processability. Characterize candidate filled-elastomer material systems through thermal, mechanical, and physical property testing. Perform propellant interface & bond line characterization with typical high performance propellants. Compare performance of candidate systems with state-of-the-art elastomeric insulation baseline through analyses of the physical properties and thermomechanical performance. Reference 5 provides typical physical properties for state-of-the-art Kevlar/EPDM insulation materials in Table 1, as well as thermal and erosion data for the Kevlar/EPDM designation ARI-2727. This reference (or another relevant reference for state-of-the-art solid rocket motor internal insulation material properties) may be used for comparison with new materials to determine the relative improvements in performance. Offerors should include a cost analysis of candidate materials for comparison with state-of-the-art materials.

PHASE II: Fabricate and test novel insulation material systems to verify improvements in thermo-mechanical properties. Perform relevant coupon level laboratory testing (e.g., plasma or oxyacetylene torch testing) to compare performance with state-of-the-art baseline insulation and down-select candidate(s). Perform sub-scale motor testing with down-selected candidate(s) to demonstrate performance. Provide evidence of process viability for large scale production while focusing on low cost, efficiency, and minimizing environmental impacts while maintaining the necessary material performance.

PHASE III DUAL USE APPLICATIONS: Demonstrate the new insulation material’s thermo-mechanical capability in a relevant environment. Anticipated benefits for tactical rocket motors include improved motor efficiency, supporting multi-mission and extended range goals, reduced system mass and parasitic volume, and materials and processing techniques for low cost, sustainable, domestically-manufactured critical materials. Phase III applications for integration exist across the portfolio of current tactical Army systems and Technology Efforts through the replacement of thicker internal rocket motor insulation. Programs that would benefit from this innovation are not limited to Army systems, but extend throughout the Department of Defense and to the National Aeronautics and Space Administration. Commercial applications for this type of low cost, high performance elastomeric insulation material may exist in the private space industry and other commercial areas as well.

REFERENCES:

  • A.M. Helmy, “Thermal Analysis of Solid Rocket Motor’s Heat Insulation Materials,” AIAA-83-1438, AIAA 18th Thermophysics Conference, 1-3 June 1983, Montreal, Canada.
  • Steven A. Kyriakides, Scott W. Case, “Processing Mechanical Test Specimens of Charred Solid Rocket Motor Insulation Materials,” Journal of Spacecraft and Rockets, Vol. 46, No. 6, November-December 2009.
  • D.L. Misterek, K.K. Pace, “Motor Internal Insulation Design Verification & Non-Conformance Analysis,” AIAA Joint Propulsion Conference, 32nd, Lake Buena Vista, FL, 1-3 July 1996.
  • V.F. Hribar, “A Critique on Internal Insulation Materials for Solid Propellant Rocket Motors,” J. Spacecraft, Vol. 3, No. 9, Revision 9 May 1966.
  • Catherine A. Yezzi, Barry B. Moore, “Characterization of Kevlar/EPDM Rubbers for Use as Rocket Motor Case Insulators,” AIAA-86-1489,” AIAA 22nd Joint Propulsion Conference, 16-18 June, Huntsville, AL.
  • W.F.S. Tam, M. Bell, “ASRM Case Insulation Development,” AIAA-93-2211, “AIAA 29th Joint Propulsion Conference, 28-30 June 1993, Monterey, CA.

KEYWORDS: Thermostructural composites, ablation, erosion, solid rocket motor insulation, filled elastomers

 

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