Redesigning the space shuttles solid rocket motor seals

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 382 KB
• Volume: 1996
• Category: Article
• ISSN: 1350-4789
• DOI: 10.1016/s1350-4789(96)80170-x

✦ Synopsis

Last month's launch of the space shuttle Endeavour, was marked by the kind of cold weather that caused the explosion of the Challenger 10 years ago. In preparation, technicians pumped hot air in to keep the craft warmed, and circulated heated nitrogen gas over the instruments that direct the booster rockets. Protective warming bands were also placed over the O-rings that seal the joints of the solid rocket boosters. Faulty O-rings, normally flexible and pliable, but frozen stiff by the cold weather, were identified as the reason for the Challenger explosion, which resulted in the loss of seven astronauts. The following article reports on the improvements that have been made to sealing the solid rocket motor field joints since the disaster. Investigation Scrutiny of the Challenger launch videos showed smoke coming from a point low on the side of the right-hand solid rocket booster (SW) and shots taken of the vehicle in flight revealed spurts of flame from the same location.

Constructed from hollow cylindrical sections, the boosters are held together by field joints which should form a leak-tight seal, and retain the aluminium perchlorate fuel. In the event, a burning jet of combustion gas penetrated the O-rings of the field joint, and was able to reach the external fuel tank.

The rubber O-rings were designed to accommodate bending and flexing in the field joints under launch and flight stresses. At normal temperatures, the O-rings were sufficiently pliable to act to seal off gaps almost instantaneously, but the stiffness of cold rings meant response was slower, and there was time for intensely hot exhaust gas pass through. The O-ring rubber melted, and left a path for more to follow.