Astronaut Carlos Noriega waves toward his spacewalk partner, Joe Tanner, during the second of three spacewalks of the last space shuttle mission. Part of the newly-deployed solar array structure is at the top of the frame. Photo: NASA

An instrument used to measure the electrical charge that builds up on the international space station as it plows through the tenuous extreme upper atmosphere indicates spacewalking construction workers need not fear potentially dangerous discharges.

Space station flight director Jeff Hanley said today recent data from the floating potential probe, an instrument installed during a shuttle mission in December, shows charge buildups in the range of eight to 10 volts.

Data from the instrument stopped flowing shortly after it was installed, but Hanley said it is once again functioning and engineers are analyzing the results.

"This arcing business is a theoretically predicted phenomenon under certain ideal conditions," Hanley said. "The FPP data we are gathering, we are hopeful will demonstrate that the phenomenon as it is modeled on the ground thus far is modeled too conservatively and in fact, it is not as pronounced an effect. That's our hope.

The FPP is attached atop the station. In keeping with construction tradition, a picture of an evergreen tree was attached to mark the topping out of the "building". Photo: NASA TV/Spaceflight Now

"The vehicle potential's on the order of a few volts," he added. "This microarcing phenomenon isn't expected to start having any kind of effect until the vehicle potential gets up toward 80 to 100 volts. That's what the plasma team tells us."

The station is equipped with two so-called plasma contactor units, or PCUs, that emit a stream of xenon atoms into space to prevent large charges from building up. Data from the floating potential probe shows the PCUs reduce the already low voltage by three to five volts.

"All indications are the PCUs are doing their job," Hanley said. "We've taken data both with the PCUs on and off and we do see a difference."

Station commander William Shepherd, Yuri Gidzenko and Sergei Krikalev are gearing up for arrival of the space shuttle Atlantis late next week and installation of the $1.38 billion Destiny laboratory module.

The Expedition 1 crew members are about to eat fresh fruit in the form of oranges onboard the Zvezda service module. From the left, are Yuri Gidzenko, Bill Shepherd and Sergei Krikalev. Photo: NASA

Launch currently is targeted for Wednesday at 6:11 p.m. EST. If all goes well, Atlantis will dock with the station at 11:56 a.m. on Feb. 9. The lab will be attached the next day to the multi-hatch Unity module's forward port.

Atlantis is scheduled to depart on Feb. 16. About one week later, around Feb. 24, Shepherd and company will strap into their Soyuz ferry ship and move it from the Zvezda command module's aft port to a downward-facing port on the Zarya module.

An unmanned Progress supply ship, tentatively scheduled for launch around Feb. 26, will dock at the command module's aft port two days later.

Along with preparing the station for arrival of Atlantis' crew, the Alpha astronauts are continuing work to inventory on-board supplies and equipment.

Hanley said more than 10,000 individual items are on board, the vast majority of which feature barcodes for use with a computer database listing each item's identity and stowage location.

But Hanley said several thousand items - 20 percent or so - were launched before the current inventory system was perfected.

Expedition 1 mission commander, Bill Shepherd, is pictured sorting through equipment in a docking compartment aboard the international space station. Photo: NASA

"Of the gear that was stowed on board the station, there's a percentage of it, maybe 20 percent, that very early in the program went up to the vehicle without the kind of bar code tracking system number on it that we currently use to track these things," he said.

"That includes some individual pieces of equipment and some bags these things were stowed in. So the crew is pulling these things out, they're going through where these things are stowed, they're actually applying bar codes to the bags and items and then logging that into their inventory management database. That takes a good amount of time to do

"We've given them blocks of time over the last two or three weeks to devote to doing nothing but that."

Otherwise, he said, the station is in generally good health. One of the Zvezda module's batteries requires a bit of manual care to stay properly charged, but so far it is carrying its load as required.

Russian engineers are still troubleshooting apparent communications problems with on-board Russian spacesuits. Hanley said engineers suspect the problem involves interference inside the Zvezda module where the suits were inspected and tested.