NASA - National Aeronautics and Space Administration

Improving Shuttle Safety

This is the fourth in a series of articles highlighting Glenn's research and test efforts in improving space shuttle safety.

Composite Overwrapped Pressure Vessels

Image above: NASA Kevlar COPV shuttle helium tank. Credit: NASA

For over 25 years, Kevlar Composite Overwrapped Pressure Vessels (COPV) have been used to store inert gases such as helium and nitrogen under varying degrees of pressure onboard the space shuttle. Due to the age of these vessels, a NASA Engineering Safety Center team is determining if the COPVs are safe to fly in future shuttle missions. A typical vessel consists of a titanium liner overwrapped with a Kevlar composite system. The purpose of the liner is to prevent gas leakage and provide some load sharing. The Kevlar fiber overwrap provides the primary load carrying ability, but it can fail under sustained loading due to static fatigue. In 2004, Glenn’s Life Prediction Branch conducted an in-depth structural safety analysis of the Kevlar fiber and overwrapped vessels. More recently, members of the branch collaborated with other NASA centers, industry and university partners to utilize advanced modeling techniques to determine the probability for vessel failure during various periods within a mission and recommend a single vessel or a system of vessels for future shuttle missions. Current work is focused on testing and analyses on samples from actual COPVs to validate the analytical models.

Team: Dr. Pappu Murthy and John Thesken, Life Prediction Branch; Dr. James Sutter, Polymers Branch; Duane Revilock, Structural Mechanics and Dynamics Branch; Dr. Jeff Eldridge, Durability and Protective Coatings Branch; and Dr. Frances Hurwitz, Ceramics Branch

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(Emily Groh, ANLX/Exploration Systems Division, contributed to this article)