Failure Mode Avoidance of Solid Rocket Motor Pressure Monitoring Joint Seals
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Mode Avoidance of Solid Rocket Motor Pressure Monitoring Joint Seals V. Murugesan . P. S. Sreejith . A. K. Anilkumar . V. Kishorenath
Submitted: 11 January 2017 ASM International 2017
Abstract The sealing joints used for pressure monitoring of solid propellant rocket motors (SRMs) of launch vehicles are very critical, as they are large in number, and leak through any of them is a single point failure mode. Identification of failure modes and its prevention is the key for reliable performance of an SRM. Failure modes are identified and the failure mechanisms of different seals in the pressure monitoring system studied through investigative tests with deliberately induced variations in the design parameters and nonconformance. Systematic analysis is carried out for the proposed designs through a failure mode effects analysis (FMEA), failure modes ranked in accordance with Risk Priority Number (RPN) and reliability of the joints worked out from the data. Design concerns are analyzed, alternate designs explored and innovative design solutions evolved. The effectiveness of the final design is brought out quantitatively by reduced RPN ratings and quantum jump in the reliability. Critical design, process and quality control parameters were identified, and procedures to ensure them evolved for failure mode avoidance. Keywords Failure modes Risk Priority Number (RPN) Solid rocket motor (SRM) Reliability Sealing joints O-ring
V. Murugesan (&) A. K. Anilkumar V. Kishorenath Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India e-mail: [email protected] P. S. Sreejith Cochin University of Science and Technology, Cochin 682022, India
Introduction Solid propellant rocket motors (SRMs), because of their simple design and less number of subsystems, are more reliable compared to more complex liquid propulsion systems. The solid rocket motors come in different types and sizes and deliver thrust from 2 N to over 12 million N. They are used in a wide range of applications in launch vehicles as main propulsion systems, as strapon boosters and as special purpose motors [1]. However, being a one shot device, its reliable performance cannot be verified by an acceptance test as in the case of a liquid engine. It is assured by ensuring adequate design margins and adhering to the quality standards and procedures throughout the product life cycle. A major challenge in the reliability assurance of an SRM is ensuring leak tight joints. An SRM comprises of factory joints such as weld joints, and field joints like segment joints and joints for pressure monitoring to assess the motor performance. The factory joints are testable and are well protected against thermal environments. The motor segment joint, a field joint, has undergone many changes world over, after Space Shuttle Challenger accident on January 28, 1986, in terms of seal redundancy and constraining the deformation of the cylindrical sections at seal location, thus making it highly reliable [1–3]. However, the
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