Riding atop a towering 60-story pillar of flame, the spaceship soared up the U.S. East Coast in pursuit of the international outpost, which was flying high over the Indian Ocean due south of the Bay of Bengal at the time.

The spectacular 8.5-minute climb into orbit - which was visible along most of Americas southeastern seaboard - set the stage for what many consider one of the most challenging space construction missions of all time.

"Its one of the most complex station assembly flights that we will conduct," NASA shuttle program manager Ron Dittemore said.

With Discoverys robot arm serving as a construction crane, the six-man, one-woman crew will attempt to put in place a new shuttle docking port and the first piece of the stations metal spine, which eventually will span an area longer than a football field.

Four consecutive days of spacewalking construction work then will have to be carried out to wire up the new station additions, electrically linking them to an outpost now made up of three permanent wings.

Any major slip-ups, meanwhile, likely would scramble an impending six-year series of about 40 additional U.S. shuttle and Russian rocket flights that will be required to raise the rest of the $60 billion station, a joint project of 16 nations on four different continents.

"You can no longer think of what we do as a series of individual shuttle flights," said NASA space station project manager Tommy Holloway.

~

The long journey

"We need to think about it as a journey -- a set of overlapping missions -- all interrelated and coming together to create the International Space Station."

And that fact is not lost on Discoverys crew.

"Every mission in the assembly sequence is critical. Each one depends on the one that goes before it," Discovery astronaut Pam Melroy, who is only the third woman to pilot a shuttle, said in a recent interview with SPACE.com.

---

---

"So I think in that sense, everybody on these construction flights feels a great deal of responsibility because they know they can hold up the whole chain of events," added crewmate Jeff Wisoff.

Originally slated to launch last Thursday, Discoverys flight was delayed six days by a pesky pair of technical problems, windy weather in the Cape Canaveral area, and the discovery of a loose metal pin lodged in a critical area between the ship and its 15-story external tank.

Technicians completed an overnight scramble early Wednesday to snatch the loose pin from its dangerous resting place, clearing the way for shuttle fuel-loading operations later in the day.

The weather, meanwhile, threatened to force yet another delay as foreboding clouds formed and a light rain fell around the KSC area during the day.

A tornado-like waterspout was spotted near the shuttles seaside launch pad as the astronauts were boarding Discovery, but the weather calmed down enough for NASA to send the ship and its space station construction workers on their way.

Now Discoverys crew -- which includes six U.S. astronauts and a Japanese mission specialist -- will spend the next two days closing a wide gap between the orbiting craft.

Flying in formation at 25 times the speed of sound, Discovery and the station are scheduled to link up some 240 miles (384 kilometers) above Earth around 1:43 p.m. EDT (1743 GMT) Friday.

~

Construction ahead

Hard-hat work at the orbital construction site will begin Saturday as Japanese astronaut Koichi Wakata uses the shuttles robot arm to pluck a nine-ton piece of metal framework from Discoverys cargo bay and then mount it atop the 13-story station.

A daunting quartet of back-to-back spacewalks then will be carried out over the following four days to hook up the station truss, set up the new shuttle docking port and deploy the outposts main communications antenna.

Also on the crews to-do list: Test-flying Buck Rogers-style jet backpacks designed to enable spacewalking construction workers to maneuver back to the station if standard safety tethers snap, casting them adrift in space.

The jetpack test-flights are considered crucial because NASA still faces an additional 155 spacewalks to complete station assembly between now and April 2006.

"The spacewalking challenge we have ahead of us is just tremendous," said former NASA chief astronaut Robert Cabana, now a senior space station project manager.

The crew also will spend a day inside the station, finishing electrical hook-ups to the truss and delivering supplies for the outposts first full-time tenants, who are due to take up residence at the station in early November.

And if all goes well, Discovery will depart the station Oct. 20 and then head for a 2:10 p.m. EDT (1810 GMT) Oct. 22 landing at KSC.

That, in turn, would clear the way for seven more station-building shuttle missions in the next 12 months, and barring delays, an outpost with as much habitable space as a three-bedroom house by the end of 2001.

"Weve got the foundation laid, and now were ready to get to the heart of the construction project," said Daryl Schuck, a lead engineer in NASAs spacewalk projects office at Johnson Space Center in Houston.

"This is just the beginning," added Cabana. "In the end, its going to be a world-class laboratory thats up there seven days a week, 365 days a year, doing great science. And I cant wait to see it keep going and grow in the months and years ahead."