Image: Atlantis
Win McNamee  /  Getty Images
The space shuttle Atlantis sits on its launch pad at NASA's Kennedy Space Center on Thursday. NASA has decided to go ahead with a launch attempt on Friday, after weighing concerns about the shuttle's electrical system.
updated 9/8/2006 10:44:35 AM ET 2006-09-08T14:44:35

The long wait neared an end for the space shuttle Atlantis and its oft-delayed space station construction mission as NASA restarted its stalled countdown clock, moving toward a planned Friday morning liftoff.

The weather forecast looked mostly clear for a scheduled 11:40 a.m. ET launch as NASA managers Thursday evening cleared the latest glitch that had delayed the takeoff: a baffling short in a 30-year-old motor in one part of one of the shuttle's three electricity-generating fuel cells.

Atlantis was supposed to launch Aug. 27, but was delayed first by a lightning strike at the launch pad, then by the approach of Tropical Storm Ernesto. It was held up again early Wednesday morning when the fuel cell problem arose right before the shuttle's tank was filled.

But the wait for this 11-day blue-collar construction mission goes back far longer for Atlantis and its six-astronaut crew.

One of the two girders that Atlantis is hauling up to the international space station has been waiting at Kennedy Space Center for nearly seven years. Atlantis' mission is to bring up two girders and solar panels — weighing 17.5 tons — to the orbital outpost.

Originally, the mission was slated for May 2003, but the February 2003 Columbia accident put the mission on hold for more than three years. Atlantis, which has flown 26 times, hasn't launched since October 2002.

Restarting construction
Atlantis' astronauts will restart construction on the half-built international space station for the first time since the Columbia disaster.

"It's been a long road. There's been a lot of folks that have spent the better part of the last seven years of their careers here at the space center working on it," payload manager Robbie Ashley said late last month.

Slideshow: Month in space: Future frontiers NASA has only five-minute launch windows on Friday and Saturday — and Saturday was a last-minute addition after talks with Russian space officials — before it has to scrap launch plans for at least two and a half weeks.

The Russians are launching a three-person Soyuz capsule to the space station on Sept. 18, and Atlantis has to leave the station before the Soyuz arrives to prevent a cosmic traffic jam.

A Saturday launch would create a delicate job for above-the-air traffic controllers because within 21 hours three spaceships would come and go from the space station. If Atlantis launches Saturday, it would undock from the space station at 9 a.m. ET on Sept. 18, just nine hours after the Soyuz would launch. And 12 hours after the shuttle undocks, an unmanned Progress resupply ship also leaves the space station.

Analyzing the electrical problem
But to even get to that point, NASA managers had to convince themselves that the baffling electrical problem wouldn't be a safety risk — something they did over the objections of NASA's safety managers and the makers of the fuel cells. Shuttle engineers deduced — but couldn't prove — that the problem was likely from thinning wires that caused a coolant pump motor to give errant results.

The 30-year-old motor last flew in 1999 on a mission that had a fuel cell problem, but it was likely unrelated to the problem that cropped up days ago, said Steve Poulos, shuttle orbiter projects manager.

Engineers calculated that the two-week job of changing fuel cells would not only delay a launch but could cause more problems than leaving the fuel cell stay as is, Poulos said.

"I don't have a concern that we're going to lose this fuel cell," Poulos said.

Concerns eased
NASA safety managers and fuel cell-maker UTC Power both recommended swapping out the fuel cell, fearing that it could fail. But a failure wouldn't be a safety problem and would only require a shortened mission, said shuttle program manager Wayne Hale.

Late Thursday night, the company said it was fine with the decision to fly.

"We're very comfortable with flying," said Henry DeRonck, general manager for space at UTC Power. "There is very low risk of anything getting further worse."

If the launch isn't completed by Saturday, NASA could open up launching opportunities in late September and early October by relaxing a requirement that launches take place in daylight.

The rule was implemented for the first few flights after the Columbia accident so NASA can check if foam comes off the external fuel tank and could damage the shuttle's heat shield as it did Columbia's.

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