Astronaut Bill McArthur rides the shuttle's robot arm during a spacewalk on the most recent space station assembly mission in October. Photo: NASA

The astronauts will take a day off after the first spacewalk to recharge their spacesuits and to give ground engineers time to activate, check out and charge up the P6 array and its batteries.

Once battery charging is complete, the P6 system will be fully operational and capable of maintaining its own health if the shuttle had to depart unexpectedly.

"But it cannot deliver any power to any other pieces on orbit," Reeves said. "That's the primary task of EVA-2, for the crew to go out and do the patch panel reconfiguration out on Z1. This enables P6 power now to be delivered to the Russian segment and the Z1.

"At that time, we can begin heating the (Unity) node up so the crew can go in there later on."

The second excursion is scheduled to begin around 2 p.m. on Dec. 5.

Following the electrical reconfiguration work, Tanner and Noriega will move an S-band antenna array to the top of P6 that was temporarily mounted on the Z1 truss during a shuttle flight in October. They also will carry out additional work to ready the radiator for deployment during the lab mission in January.

"The exciting part of EVA 2 will be when we move the SASA antenna to its operational position on top of P6," Noriega said. "Joe will do the initial work on the antenna, disconnecting it from its current location and disconnecting all the cables on it. He'll be doing this off the arm.

He'll be moved by Mike Bloomfield, driving the arm, to a position as high as the arm can reach where I will be waiting in a foot restraint to receive the antenna from him.

"It's still not high enough to get us where we need to be and we need to be restrained when we're carrying this large delicate object," Noriega said. "So Joe will carefully rotate me in my foot restraint around so I'm now pointing toward the highest point on the station where he will ingress the work site and I'll hand the antenna back to him and we'll connect it. It's a little bit of a ballet.

"While he's finishing up that, I'll be working a patch panel on Z1 where we redistribute the power between the Russian segment and us. We will also be connecting very important fluid connections, which Joe will do off th arm, that will provide the initial cooling for the U.S. segment, especially the lab. We have several get aheads, preparing the radiators for deployment."

The STS-97 crew portrait shows Carlos Noriega and Joe Tanner in spacewalking suits along with Mike Bloomfield, Marc Garneau and Brett Jett in their launch and entry suits. Photo: NASA

A third and final spacewalk is planned for Dec. 7. The goal is to install a device called the floating potential probe experiment on top of the P6 truss and an antenna that will relay data from the device into the space station.

The FPP will monitor the electrical environment around the station to give flight controllers insight into the operation of devices called plasma contactors that were installed during the October shuttle flight.

"The source of this issue or concern comes from the fact that the solar arrays on P6 are so big and high voltage," Hanley said. "There is a concern that this high voltage array, which is oriented toward the velocity vector, will interact with the ambient charged environment around the station, resulting in a potential difference between the station structure and the environment.

"When this potential difference occurs," he said, "you could have electrostatic discharges."

Translation: Potentially dangerous arcing that could pose a shock hazard to spacewalkers and degrade the performance of special coatings intended to help control hull temperature.

The plasma contactors slowly release xenon gas into space to provide what amounts to a short circuit between the Z1 truss and the surrounding plasma.

"It takes electrons that might build up on the truss and throws them back into the plasma to complete the circuit, thereby eliminating this problem," Hanley said.

But the plasma contactors do not provide any telemetry showing how they are working. The floating potential probe will monitor the electrical environment to provide additional insight.

"The crew will go back out to install the floating potential probe experiment, which is a self-contained experiment with its own solar array power," Reeves said.

"They will transport it to the very top of P6, install it on a deck near the beta gimbals, then they will come back down to the node where they will install an antenna. Then they will connect up some cables to take the signal inside the node for later use."

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