Hydraulic System Breakdown Spoils Test of New Rocket Booster O-Rings

Disappointed rocket engineers said Friday the failure of a hydraulic system during a shuttle booster test-firing prevented them from gathering key data about how new O-ring joints respond to external forces.

The 52-foot subscale booster was fired Thursday at Marshall Space Flight Center in the first of a series of tests to subject the sensitive joints to both internal and external forces similar to those experienced by real boosters at liftoff.

“We’ve looked at some more data since (the test) . . . and we went through the motor case joints and other elements of the solid rocket motor and they performed as expected,” said John McCarty, director of the propulsion laboratory at Marshall. “There were no problems or any indications of an external leak.”

A NASA statement said the test accomplished 90% of the agency’s objectives.

But one of the major objectives of the test was to evaluate how the joints respond to the external forces transmitted to shuttle boosters by three giant struts that attach the rockets to the shuttle’s external fuel tank.

Such dynamic “loads” tend to push the joint members apart slightly, which can create a deadly leak path for hot gas and flame, and it was a joint rupture that destroyed Challenger last year.

Special piston-driven struts on the test booster’s firing stand were designed to mimic those forces.

“There are three struts that go from the solid rocket motor to the external tank,” McCarty said. “Each of those struts is replaced (in the test) with a hydraulic cylinder, which introduces loads. Once one of the three begins to work improperly, we shut down all three. That’s what happened.