Vulcan’s upper stage failed due to higher stress and weaker welds

Enlarge / United Launch Alliance's Vulcan rocket completes a "flight readiness firing." (credit: United Launch Alliance)

United Launch Alliance has identified the root cause of a failure that destroyed the upper stage of its Vulcan rocket in late March. According to the company's chief executive, Tory Bruno, the Centaur V upper stage failed due to higher-than-anticipated stress near the top of the liquid hydrogen propellant tank and slightly weaker welding.

Bruno outlined the nature of the failure and steps the company is taking to remediate it during a teleconference with space reporters on Thursday. He said United Launch Alliance is working toward flying the heavy lift Vulcan rocket on its debut mission during the fourth quarter of this year.

Tank failure

The Centaur V upper stage was destroyed during pressure testing at Marshall Space Flight Center in Alabama on March 29. Bruno said this was the 15th test in a series of 45 tests to qualify the Centaur stage for all potential mission profiles. However, about halfway through the test the hydrogen tank started leaking, and over the course of four and a half minutes the leak expanded.