Nondestructive Testing Inspection Plan
In each new motor program, there are normally two methods for controlling motor case reliability. One method is to accumulate and analyze data on failures that occur during hydrostatic proof tests and motor static and service firings, then modify the design according to the results of the failure analysis. The other approach, used in combination with the method above, is to employ a detailed and comprehensive program of material and fabrication-process control throughout material procurement...
Motor Case Loads 1
The case-loading profile shall include all individual design loads or the worst combination of design loads. The loading profile shall be determined by evaluation of any and all of the following loads. All axisymmetric and local design loads for definition of design load, see sec. 2.3.1.1 , including dynamic loads sec. 3.3.7 , should be resolved into membrane loads to determine the critical design loading condition. The critical case loading condition, or worst critical combination loading,...
Material Properties
A summary of the properties of some of the alloys commonly used in the aerospace industry is provided in table I. A more complete treatment of material properties including fracture toughness , forming characteristics, and weldability may be found in references 51 and 52. The commonly accepted sources of property data for some metals used in motor case design are reference 51 and references 52 to 55. These documents also provide the designer with general information on both heat-treatment...
CaseConfiguration Considerations
The motor case configuration can have a significant influence on material selection. For instance, the size of existing quench and temper heat-treating facilities with controlled atmosphere limits their use to motor cases of 140-in. diameter or less. Therefore, the material for cases above this size limit is selected from materials that can be fabricated without a final quench and temper heat treatment. See table I. Also, the number and location of case welds are influenced by the relation of...
Design Safety Factor 1
The case shall have the minimum design safety factor required to obtain the specified reliability. A design safety factor should be used in the design of rocket motor cases to account for contingencies e.g., underestimation of case loading, underestimation of case stresses, undetected variations in material properties, and undetected manufacturing deviations . The design safety factor should not be used for accumulation of conditions where variables are expected to occur. For example, the limit...
References
1. Alexander, R. V. Cost and Performance Considerations in the Selection of Structural Materials for Ultra-Large-Size Booster Motors. J. Spacecraft Rockets, vol. 1, no. 1, Jan.-Feb. 1964, pp. 62-67. 2. Alexander, R. V. Apodaca, A. R. and Fournier, C. A. Cost and Performance Considerations in the Selection of Structural Materials and Propellants for Multi-Stage Solid Rocket Vehicles. Preprint 2415-62. ARS Structural Materials Conference, April 1962. 3. Alexander, R. V. and Fournier, C. A. A...
Structural Dynamics 1
The case shall withstand all transient and steady-state dynamic loads, or the worst combination of dynamic loads and critical static loads. Detailed dynamic analysis of the particular stage and the vehicle should be performed to insure that the motor case design is adequate for all imposed transient and steady-state dynamic loads. The dynamic loads imposed on the motor case as determined from the individual dynamic analysis should be integrated into the case structural analysis sec. 3.3.6 . The...
Design Optimization
Motor case design is governed by the motor and vehicle requirements, such as performance characteristics including motor propellant grain design , envelope constraints, mission profile, and other components within the individual stage and the vehicle. These factors are interdependent in their influence on the case design. In some programs, the basic case design parameters, including length-to-diameter ratio, external constraints, internal pressure, motor case flight loads, and propellant mass...
Rocket Motor Case
The objectives of the motor case design are to establish the case configuration, select the structural material, and establish a case structure that results in either optimum performance or optimum cost effectiveness, depending on the specific program objectives and design requirements. Generally, the optimum case design is the least expensive one that satisfies all the mission objectives while not violating any imposed constraints i.e., the most cost effective . Typical solid rocket motor and...