Astronaut Bill McArthur wears spacewalking suit during training for his upcoming mission. Photo: NASA-JSC

Assuming Z1 installation goes smoothly, Chiao and McArthur will stage the first of the crew's four spacewalks the next day.

"After the Z1 has been berthed and after Pam has gotten the CBMs to connect the Z1 physically to the structure, Bill McArthur and I will go out on the first EVA (spacewalk) and begin outfitting the Z1 truss," Chiao told reporters.

"We'll be connecting cables between the Z1 and the node and we'll also be relocating the S-band antenna as well as taking the KU dish out, attaching that to a boom and then rolling that boom out. We'll also be transferring one of the tool boxes over to its location on the Z1 truss.

"We're hoping everything goes very smoothly and we'll get a good kickoff on the first EVA to set the tone for the rest of the spacewalks," he said.

The next day, Wisoff and Lopez-Alegria will float into Discovery's cargo bay to assist Wakata in attaching a pressurized mating adaptor to Unity's nadir hatch.

"It's called PMA-3 and it's held in the back of the space shuttle on a Spacelab pallet," Wisoff said. "It's bolted on and the only way to get it off is to go out and manually undo these bolts. So Mike and I will go out on EVA 2, go to the back of the payload bay, undo all the bolts on PMA-3 and then Koichi will pick it up with the arm and carry it over to the nadir port of the node."

Animation shows the black PMA-3 being attached to Unity by the shuttle's robot arm above the nose of Discovery. Photo: NASA TV/Spaceflight Now

Attaching PMA-3 is especially tricky because Wakata will have limited visibility and little margin for error. He will be assisted by the Canadian-built Orbiter Space Vision System, which uses television cameras, computers and targets to compute a module's exact position and orientation.

"Mike and I will position ourselves on opposite sides to watch it, to make sure the alignment is good," Wisoff said. "We have a Space Vision System to help us do that, but if it should fail or not work as planned, Mike and I will already be outside and positioned to help give Koichi directions on how to align it.

"Once it's attached to the node, we'll set up the arm," Wisoff continued. "I'll get on the arm and Mike will undo the umbilicals that are on the mating adapter. Then we'll go and attach all those umbilicals to the node to give the PMA the necessary power and data that'll be needed later."

The space station's first set of U.S. solar arrays will be mounted atop the Z1 truss in December. The electricity generated by the arrays will be converted to the proper voltage by two DC-to-DC converter units, or DDCUs, mounted on the Z1 truss.

Chiao and McArthur will install both DDCUs during the third spacewalk. With Chiao anchored to the end of the robot arm, Wakata will move him between the shuttle and the truss to retrieve the DDCUs.

"Koichi's going to thread the needle on this one and stick Leroy, on the end of the arm, between the edge of the payload bay and underneath Z1 so he can go to the sidewalls, release these DC-to-DC converter units and then bring them back up and put them on the right side of the space station," McArthur said.

An artist's concept of the station with solar arrays deployed following the STS-97 mission in December. Photo: NASA

If all goes well, Wisoff and Lopez-Alegria will carry out the mission's fourth and final spacewalk the next day. During the first part of the excursion, the duo will prepare the Z1 for the attachment of the P6 solar arrays in December.

The 24,547-pound P6 array will consist of a base that will attach to the Z1 truss. From that base, four panels will unfurl stretching 240 feet from tip to tip, or one-and-a-half times the current length of the three-module space station.

The huge arrays will generate nearly 100 kilowatts of power and make the station the third brightest object in the night sky when it passes overhead at dawn or dusk.