Jessica Schoenbauer 1/24/08 External Structure Tank Materials Solid Rocket Motor Casings

Mass & Cost for a Solid Rocket Motor Case Assumptions: Thin-walled pressure vessel Maximum Expected Operating Pressure (MEOP) = 1600psi (~11MPa) Factor of Safety = 1.25 Radius = 0.709m, Length = 6.317m –Vanguard for 5kg payload Inflation since 2005 = 4.3% Cylindrical in shape Structures Group

Recommendations Future Work Steels such as D6aC look like good options Fiberglass also looks like a good option, but the mass and cost listed may increase if the material is not stiff enough to maintain pressures Future Work Integrate manufacturing into the total cost Structures Group

Backup Slides - References 1. Humble, Ronald W., Henry, Gary N., and Larson, Wiley J., Space Propulsion Analysis and Design, The McGraw-Hill Companies Inc., New York, 1995. 2. Callister, William D. Jr, Fundamentals of Materials Science and Engineering, 2nd edition, John Wiley & Sons, Inc., Hoboken, NJ, 2005. 3. DeVries, D. and Aadland, J. “Electonic Safe and Arm (ESA) Device for Solid Propellant Rocket Motor Initiation,” 37th AIAA/ASME/SAE/ASEE JPC Conference and Exhibit, Salt Lake City, Utah, 2001. 4. “Department of Defense Handbook: Metallic Materials and Elements for Aerospace Vehicle Structures,” MIL-HDBK-5J, 31 January 2003 5. “Consumer Price Index”, U.S. Department of Labor, January 2008. [http://www.bls.gov/cpi/home.htm. Accessed 1/23/08] Structures Group

Backup Slides – Calculation for motor case thickness pb = burst pressure (Pa) MEOP = maximum expected operating pressure (Pa) fs = factor of safety tcs = motor case thickness (m) rcs = case radius Ftu = ultimate tensile strength of case material (Pa) tcs rcs rcs Geometry of a Cylindrical Motor Case based on Humble, Henry, and Larson, Ref. 1. Structures Group

Backup Slides - Quotes “A typical large solid propellant rocket motor has a maximum expected operational pressure (MEOP) of approximately 1600 psi.” – DeVries and Aadland, Ref. 3. In reference to composite materials: “Some of the mass savings is lost because these materials are not as stiff…, so large deflections are possible…Often stiffness concerns of this type override strength considerations, thus increasing the mass of the composite case above its minimum value solely to retain internal pressure.” Humble, Henry, and Larson, Ref. 1. “Composite structures sometimes employ a higher factor of safety because they can be damaged easier than metal cases and because strength can degrade from temperature and humidity extremes as well as aging.” Humble, Henry, and Larson, Ref. 1. “average consumer prices have risen 4.3 percent since June 2005.” Ref. 5. Structures Group

Backup Slides – Excel data for motor case Note: Quoted prices for the composite fiber materials used the pre-preg form. Structures Group