There is a continuing effort to develop improved O rings for sealing joints in solid-fuel rocket motors. Following an approach based on the lessons learned in the explosion of the space shuttle Challenger, investigators have been seeking O-ring materials that exhibit adequate resilience for effective sealing over a broad temperature range: What are desired are O rings that expand far and fast enough to maintain seals, even when metal sealing surfaces at a joint move slightly away from each other shortly after ignition and the motor was exposed to cold weather before ignition. Other qualities desired of the improved O rings include adequate resistance to ablation by hot rocket gases and resistance to swelling when exposed to hydrocarbon-based greases used to protect some motor components against corrosion. Five rubber formulations - two based on a fluorosilicone polymer and three based on copolymers of epichlorohydrin with ethylene oxide - were tested as candidate O-ring materials. Of these, one of the epichlorohydrin/ethylene oxide formulations was found to offer the closest to the desired combination of properties and was selected for further evaluation.
This work was done by Albert R. Harvey and Harold Feldman (deceased) of Thiokol Propulsion for Marshall Space Flight Center. To obtain a copy of the report, "Resilient, Hydrocarbon Base Grease Resistant O-ring Seals for Solid Rocket Motor Applications," please contact the company at (435) 863-4123.