Hydraulic Failure Hampers Test of Shuttle O-Ring Joints

A hydraulic system failure during a shuttle booster test-firing prevented NASA from gathering vital data on how new O-ring joints respond to external launch forces, space agency engineers said Friday.

Collecting such data was a major objective of the rocket firing Thursday, but officials said the problem will be corrected for future tests and the failure will have no impact on plans to launch the space shuttle Discovery in June.

The 52-foot subscale booster was fired at the Marshall Space Flight Center in the first of a series of tests to subject new O-ring joints to both internal and external forces similar to those at liftoff.

The shuttle Challenger was destroyed last year in an explosion blamed on a joint failure. The objective of the test Thursday was to evaluate how the joints respond to the external forces, or loads, on the shuttle boosters from three giant struts that attach the rockets to the external fuel tank.

Such dynamic loads, produced by the weight of the shuttle and its external tank, cause the rockets to bend and flex slightly, which can force the joints to open up slightly. That can create a deadly leak path for hot gas, officials said.

Special piston-driven struts on the test booster’s firing stand were designed to mimic those forces. But analysis of test results showed one of the piston assemblies failed Thursday and the overall system was automatically deactivated.

John McCarty, director of the propulsion laboratory at Marshall, blamed the problem on a “misadjustment” of the hydraulic control system.