Space shuttle Columbia's science mission was postponed for the third time Friday after workers trying to fix one problem created another--they apparently left open a valve, allowing hydraulic fluid to drain out.
NASA fixed the hydraulic problem Friday and rescheduled liftoff for 6:41 a.m. PDT today.
During the 16-day mission--one of the longest shuttle flights ever--seven astronauts will conduct crystal, fluid, fire and plant experiments.
The countdown was halted just hours before Friday's launch when pressure dropped in the hydraulic line that operates Columbia's nose-wheel steering. The line was found to be a gallon low on hydraulic fluid.
Shuttle operations director Bob Sieck said workers apparently left a valve open while repairing a dangerous hydrogen fuel leak last weekend. The valve was on ground equipment hooked to Columbia.
Sieck said that the workers had followed standard repair procedures but that the rules were meant for shuttles in the horizontal position. Columbia was upright on the launch pad at the time.
Launch attempt No. 1 was scuttled Sept. 28 because of the hydrogen leak. NASA then aimed for a Thursday launch, but that had to be scrapped because of stormy weather brought by Hurricane Opal.
It's the third shuttle mission in a row to be plagued by problems. Woodpeckers damaged Discovery's fuel tank insulation; then O-rings in the solid-fuel booster rockets of Atlantis and Discovery came back scorched.
"If you look at the failures we've had, it's isolated things and sometimes they lump together," Sieck said. "You go through cycles like this of what I would call bad luck."