Space Shuttle Returns To Earth

With the shuttle Columbia back on the ground, engineers are assessing the possible impact of a short circuit during launch Friday and a potentially dangerous hydrogen leak in one of the ship's main engines. Commander Eileen Collins, the first female shuttle commander, said it's too soon to speculate about whether the anomalies represent significant issues or not.

But, she emphasized, "I think we definitely need to take a very close, hard look at what happened. We don't want this to happen again on a future mission. All the attention that's being paid by the NASA engineers, the managers and the program folks is very appropriate. We take it very seriously. We're definitely going to find out what caused it and work it out."

At a post-landing news conference, Collins' crewmates praised their commander, saying touchdown late Tuesday was so smooth several of them did not even know the wheels had hit the runway.

As for landing, Jeffrey Ashby, a former Topgun Navy fighter pilot, said Collins was "within one knot of the targeted touchdown speed and within about 100 feet of the touchdown point. It was just absolutely beautiful from where I sat. I was really impressed."

"From where I sit, coming in [nose high] as we do, I can't see out so I don't know when we land until I feel it," he said. "And I wasn't sure we had landed. It was really smooth."

But the astronauts spent most of their time at the news conference fielding questions about the two launch problems that sent a scare through mission control last Friday.

A short circuit five seconds after liftoff knocked out two main engine control computers and left the crew one failure away from an engine shutdown. In addition, the nozzle of main engine No. 3 began leaking hydrogen rocket fuel shortly after ignition. Had the leak worsened, an engine shutdown could have occurred, forcing the crew to attempt a risky emergency abort.

"The bus [circuit] short we saw during ascent, I would consider a significant anomaly that we will have to look at in depth," said Bill Gerstenmaier, shuttle integration manager at the Johnson Space Center.

"The hydrogen potential leak we saw during ascent, it looks like several of the tubes are damaged in the nozzle and it looks like we had a real hydrogen leak there," he said. "That's also a very significant problem we need to look at and work on. The team's have good plans for both of those problems in terms of troubleshooting."

Main engine nozzles are made up of more than 1,000 three-eighths-inch-wide tubes. A portion of liquid hydrogen fuel is diverted through the tubeto cool the nozzle before it is routed back to the main combustion chamber for burning.

Engineers believe three or four of the tubes making up engine No. 3's nozzle cracked, or split open, allowing up to 2,500 pounds of hydrogen to spill out during Columbia's climb to space. Collins, who examined the engine with binoculars after landing, said she saw what appeared to be three small holes in adjacent tubes running in a diagonal pattern.

During launch, the engine ran about 100 degrees hotter than expected as it gulped 4,000 pounds more liquid oxygen than its neighbors to compensate for the lost fuel. As a result, the shuttle's oxygen tank ran dry, the engines were commanded to shut down a split-second early and Columbia ended up seven miles lower than its initial target.

NASA managers say the leak did not pose the threat of a catastrophic failure. Had it worsened, operating temperatures ultimately would have climbed above pre-set limits and Columbia's computers would have simply shut the engine down. Depending on when that happened, Collins could have been forced to make a risky emergency landing in Florida or Africa. But it would not have been a catastrophic failure.

It is a serious issue nonetheless and one that will have to be resolved before Columbia's next flight in September.

By William Harwood