Rocket Problem Keeps Discovery Rooted to Pad

For the second Saturday in a row, the space shuttle Discovery stayed stuck on the launch pad, this time grounded by a fault in a rocket booster 19 seconds before its scheduled liftoff.

The satellite-delivery mission to test rocket-speed communications and study extremely hot stars was already one week overdue. It is expected to be delayed another 1 1/2 weeks.

“Thanks for the effort,” commander Frank Culbertson Jr. told launch officials before following his four crewmen out of Discovery’s hatch. “We’ll be ready to come back when you tell us.”

It was the third time in four months that a shuttle countdown was halted in the final seconds before liftoff.

A stuck valve resulted in a harrowing main engine shutdown on Columbia in March with three seconds remaining. And a countdown for Discovery’s last flight ended at the 11-second mark in April because of a bad computer circuit.

This time, the problem apparently was with one of two steering mechanisms in a solid-rocket booster.

The suspect mechanism, a turbine, was sluggish in coming up to speed, said Jim Kennedy, deputy project manager for the booster program. Discovery’s computers sensed the problem and immediately halted the countdown.

Launch director Bob Sieck estimated that it will be midweek before technicians can replace the unit containing the suspect steering mechanism. That will push the third launch attempt into the first week of August, he said.