The international space station as shuttle Atlantis left it in September. Photo: NASA

Discovery is scheduled for launch from pad 39A at the Kennedy Space Center around 9:39 p.m. EDT on Oct. 5 (0139 GMT onn 6th). As with all space station assembly flights, the exact launch time will not be determined until a few hours before liftoff based on final radar tracking of the space station.

The launch window, which will last between two-and-a-half and five minutes, will open at the moment Earth's rotation carries the launch pad into the plane of the space station's orbit. By launching directly into the target's orbital plane, the shuttle can save fuel and improve the odds of pulling off a successful flight even if engine problems develop.

At the controls for Discovery's 28th flight will be veteran shuttle commander Brian Duffy and rookie pilot Pamela Melroy, the third woman to serve as a space shuttle pilot. Their crewmates are McArthur, Lopez-Alegria, Wakata, Jeff Wisoff and Leroy Chiao.

"It doesn't seem like it's been a hundred flights," said Bill Gerstenmaier, director of shuttle program integration. "But it has and we've learned a tremendous amount during all those years.

"I think it's kind of fitting that the 100th flight comes during the build up of the space station," he added. "We've done tremendous things with the shuttle, it's been unbelievably versatile vehicle. Then to see it carry on and start building space station, which is really a huge endeavor for us, is really a neat thing to see."

After a two-day orbital chase, Duffy will guide Atlantis to a docking with the space station on flight day three - around 4:15 p.m. on Oct. 7 - less than one month after the crew of shuttle Atlantis delivered three tons of supplies and equipment to the outpost.

Animation of Discovery docking to ISS. Photo: NASA TV/Spaceflight Now

Discovery will dock at a pressurized mating adaptor extending from the Unity module's forward axial port. On the other side of the node is another pressurized mating adaptor leading to the Russian-built NASA-financed Zarya propulsion module.

Attached to Zarya's far port is the new Russian command module Zvezda, which will provide the station's initial crew quarters, computer control and the propulsion needed to keep the lab at a safe altitude. The three-module station stretches some 13 stories and masses 67 tons.

Atlantis's crew outfitted Zvezda and loaded it with supplies for the station's first full-time crew. Expedition One commander William Shepherd, Yuri Gidzenko and Sergei Krikalev, scheduled for launch Oct. 30, plan to spend four months aboard the outpost before being relieved.

But before they get there, Discovery's crew will continue station assembly, delivering the first in a series of new components that will provide the power, stability and working space needed to turn the station into a functional, permanently manned space laboratory.

And the astronauts plan to hit the deck running.

Just two-and-a-half hours after docking, the crew will open hatches between the orbiter and the station and float into NASA's roomy Unity node to prepare the common berthing mechanism on the module's zenith port for the arrival of the Z1 truss.

The common berthing mechanism, or CBM, is a complex set of interlocking motor-driven petals and latches that will firmly seal space station modules together. The system will be put to the test for the first time during Discovery's mission.