The so-called S-Band Antenna Support Assembly will serve as a ready spare in case an identical model already in use at the station fails.

Next up will be inspections of quick disconnect fittings on four ammonia coolant lines between the $1.4 billion U.S. Destiny science laboratory and the end of the station's Unity module, where the bus-sized research facility was mounted last Saturday.

One of the coolant lines sprang a leak of toxic ammonia that day as Curbeam was rigging it up. A cloud of frozen ammonia crystals enveloped Curbeam, prompting an unprecedented decontamination effort as he and Jones wrapped up their first excursion outside the station.

A radiator panel designed to shed heat generated by station computer and electronics gear will be deployed as Jones watches on, and the spacewalkers then will take on a bit of electrical work: Checking out power cables between the lab and a shuttle docking port mounted to its end.

Also on the astronauts' to-do list: An emergency drill aimed at determining whether a spacewalker can physically haul an unconscious partner back into the shuttle's airlock for medical attention during an orbital crisis.

The test originally was scheduled to be carried out during a station construction mission last October but was postponed when other spacewalking work took longer than expected.

"We call it `The Dead-Guy Test,'" Daryl Schuck, an engineer in NASA's spacewalk projects office at Johnson Space Center in Houston, said at the time.

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Considered a key emergency preparedness drill, the test calls for Curbeam and Jones to take turns "playing dead," or acting as if they are suffering from an orbital version of "the bends" - the type of decompression sickness that can make scuba diving deadly.

The idea is to haul the "incapacitated" spacewalker back to the shuttle's airlock to make sure it could be done in a real emergency.

"You can have the same type of decompression sickness on orbit doing a spacewalk, and if we ever had a crewmember have that happen to them while they're outside, they might go unconscious," NASA astronaut Jeff Wisoff said before the October flight.

"So we want to make sure it's a reasonable expectation that one crewmember can drag the other person into the airlock so we can get him some medical attention if necessary."

Two methods will be tested.

The so-called "daisy chain" method calls for a spacewalker to hook his or her waist safety tether to an incapacitated partner and then tow the unconscious astronaut into the airlock.

In the other - known as the "strap method" - the unconscious astronaut's waist tether is used to form a rope-like loop, enabling the spacewalking partner to pull an incapacitated crewmate toward safe harbor inside the shuttle.

Coming 36 years after Edward White exited the Gemini 4 capsule for NASA's very first EVA - or Extravehicular Activity - the shuttle astronauts' work outside the station marked the agency's milestone 100th spacewalk.

The first 40 of those were carried out during NASA's Gemini, Apollo and Skylab programs, and 60 since have been staged from U.S. space shuttles.

The spacewalk Wednesday was the 16th of about 165 required to build the new international station, a joint project of 16 nations on four continents.

Hatches between Atlantis and the international outpost - which also is known by the radio call sign "Alpha" - will swing open again after the planned five-hour spacewalk so the joined shuttle and station crews can continue outfitting the Destiny lab.

Atlantis remains scheduled to depart the station Friday after a final farewell and hatch-closing ceremony set for 7:18 a.m. EST (12:18 GMT) that day. The shuttle and its crew are due to land at Kennedy Space Center at 12:52 p.m. EST (17:52 GMT) Sunday.