A "Case" History in the Minuteman Reliability Program Neil E. Hoesel Wasatch Div., Thiokol Chemical Corp. George M. Hurt Allison Div., General Motors Corp. ABSTRACT Aerospace reliability programs have encountered the problem of achieving required reliability without using a costly demonstration program. This paper describes the criteria and program developed to satisfy the reliability requirements for the USAF First Stage MINUTEMAN Motor Case. A comprehensive process surveillance and analysis program by Thiokol Chemical Corporation and the Allison Division of General Motors Corporation has provided high re­liability of the large, costly cases in the MINUTEMAN program without preproduction demonstration at the allocated level of reliability for the part. This paper outlines the specifications that were used as criteria for the MINUTEMAN program along with the resulting implementation by Allison Division. Demonstration and observed reliability growth curves, in addition to missile and motor test results, supplied proof of the value of this approach BACKGROUND CONTRARY TO CLASSICAL CONCEPTS, reliability requirements can be met without large statistical demonstration programs. Thiokol Chemical Corporation and Allison Division, GMC, jointly developed an alternate program for the First Stage MINUTEMAN Motor Case that achieved the required reliability without consuming costly, large sample, destructive tests for demonstration. The quantitative reliability requirements for the MINUTEMAN ICBM Weapon System were established by Space Technology Laboratories (STL) and the Ballistic Systems Division, United States Air Force. These requirements were then apportioned among the various subsystem contractors. Thiokol, as contractor for the First Stage MINUTEMAN Motor, in turn ap­ portioned their quantitative requirements into the various motor components. The quantity of tests required to statistically demonstrate the case re­ liability value was obviously impractical. The problem that faced Thiokol reliability engineers and management was how quantitative reliability could be achieved in a newly designed concept of a large solid rocket case that was costly and could not be tested under its actual environmental conditions ex­ cept in the motor system. Historical data and previous experience were nonexistent for reliability predictions on this 65.5 in. diameter, high-strength steel case and closure. Data is necessary for prediction; but, since each test is destructive, the cost implications for the necessary sample size preclude such testing; there­ fore, a new approach had to be taken to achieve reliability objectives. Allison, as one of three case subcontractors, as­ sisted Thiokol in the development of the plan that achieved the reliability objectives. The plan contained three parts: 1. Establish design parameters and verify in sub- scale tests, 2. Establish and exercise strict process controls during fabrication, 3. Establish low frequency environmental and functional tests for materials and the case assembly. During the R&D phase, design and process analyses were conducted to isolate factors that were directly related to the reliability of the case. Sub- scale cases were loaded and tested to determine validity, pressure and temperature capability, and compatibility with other parts of the motor, partic­ ularly insulation. The process for fabrication was developed concurrently with subscale design improve­ ments to prevent degradation of the inherent reli­ ability in the full scale design. Analysis of each operation and the controls in the process proved to be an important step in assuring reproducibility of the high performance validated in early subscale tests. Once the design reliability was verified, reliability was 401 Downloaded from SAE International by University of Birmingham, Tuesday, August 21, 2018402 Neil E. Hoesel and George M. Hurt assu