Two shuttle astronauts completed the 100th spacewalk in American space history today, finishing up work to outfit the international space station and testing rescue techniques that one day could save an injured astronaut's life.

Floating in front of a camera at the forward end of Atlantis' cargo bay, spacewalkers Thomas Jones and Robert Curbeam wrapped up their third spacewalk in five days by taking a moment to mark the latest milestone on the high frontier.

"We've had three enjoyable and productive EVAs out here and yesterday in the cabin, the crew was talking about how this all started EVA-wise with Gemini 4 and Ed White back in 1965," Jones said.

"A scant seven years later - actually, only four years later - we had spacewalkers on the surface of the moon," he said. "On that desolate world, 12 people did spacewalks. Then over the next 36 years or so we've had more Skylab and shuttle experience on EVA and finally, on STS-98, we've carried out the 100th spacewalk by Americans."

"Yeah, Tom, this achievement, this golden anniversary, so to speak, is a tribute to all the people who have done spacewalks, all the people who designed the Gemini, Apollo, Skylab and now shuttle suits," Curbeam said. "And we salute all of you and appreciate your hard work and thank you so much."

Jones concluded the remarks, saying "and here we are now on a mission where the 100th EVA took place and we're constructing, using EVA techniques, an international space station and we're really proud to be a part of that construction effort."

"And we think in the years to come, in the very near future, we'll see not only construction of the space station completed, but also spacewalkers will take their place not only in low Earth orbit but back on the moon, back on the asteroids and perhaps even to Mars. We look forward to that day and we're ready for that next century of EVA. Thanks."

Today's spacewalk was the 100th in U.S. space history and the 196th in world history. It was the 60th shuttle spacewalk and the 15th devoted to assembly of the international space station.

With the completion of today's excursion, Jones and Curbeam have logged 19 hours 49 minutes working to connect and outfit the U.S. Destiny laboratory module. Here are the updated numbers:

   100...Spacewalks by U.S. astronauts
   60....Shuttle-based spacewalks
   96....Spacewalks by Russian cosmonauts
   13....Spacewalks by non-Russian crew
   		 members aboard Mir station
   03....Spacewalks by U.S. Mir crew members
   05....Spacewalks by U.S. shuttle
   		 astronauts outside Mir station
   		 
   377 hours 19 minutes....Total U.S. shuttle
                           spacewalk time
   		                   
   035 hours 26 minutes....Most EVA time in one
                           shuttle flight (STS-61)

ISS ASSEMBLY EVAs:
   16....Shuttle-based ISS spacewalks
   		 during seven missions
   00....Station-based ISS spacewalks

   021 hours 22 minutes....STS-088 (3 EVAs)
   007 hours 55 minutes....STS-096 (1)
   006 hours 44 minutes....STS-101 (1)
   006 hours 14 minutes....STS-106 (1)
   027 hours 19 minutes....STS-092 (4)
   019 hours 20 minutes....STS-097 (3)
   019 hours 49 minutes....STS-098 (3)
   
   108 hours 43 minutes....Total ISS spacewalk
   		                   time in 16 EVAs

"It's the saddest moment of my life," he said when commander James McDivitt ordered him back inside.

Three months earlier, Russian cosmonaut Alexei Leonov had become the first human to walk in space when he spent 24 minutes floating outside the Voskhod 2 spacecraft.

The Russian space program has staged 96 spacewalks in all, most of them devoted to building and maintaining a series of space stations.

But those numbers - 196 spacewalks in 36 years - will pale compared to what it will take to build and maintain the international space station.

Astronaut Gregory Harbaugh, manager of spacewalk planning at NASA's Johnson Space Center, said today NASA plans a total of 103 spacewalks through 2006 - 92 devoted to assembly and 11 to maintenance - while the Russians plan 51 assembly excursions and 14 spacewalks devoted to maintenance.

The near-term U.S. schedule calls for 22 spacewalks in 2001, 29 in 2002, 43 in 2003, 17 in 2004 and 30 in 2005. The most U.S. spacewalks ever staged in a single year is nine.

"We've called it the 'EVA Wall,'" Harbaugh said. "It is the cause of some significant concern. ... It is going to be a big challenge, we're just going to have to watch it and take it a step at a time."

Even though spacewalks are now commonplace, the experience of floating in open space still prompts awe among veteran astronauts and rookies alike.

"Guys, the view is out of this world up here!" Jones exclaimed today at one point.

"That's an understatement," Curbeam replied.

"I mean, we are speeding along toward the horizon and I can look out ... and it's just all the way out there, a thousand miles..." Jones said, his voice trailing off.

The primary goal of today's excursion was to mount a spare S-band radio antenna array on the station's hull for future use as needed; to inspect and close out fluid and electrical connectors between the Destiny module and the rest of the station; and to help deploy a large folding radiator panel.

"Wow.. there it goes, Bob," Jones radioed. "Wow! That radiator's reaching right out to the horizon!"

The astronauts also inspected and photographed the linkage mechanism connecting two huge solar wings to the top of the P6 truss. At least one of the four struts in the mechanism failed to fully lock in place when the solar wings were deployed in December.

After cleaning up the cargo bay, Jones and Curbeam closed out their final spacewalk by testing two techniques for rescuing an incapacitated spacewalker.

In one, called the daisy chain method, the active spacewalker hooked his waist tether to the passive spacewalker's suit.

In the other, called the strap method, both ends of the passive spacewalker's waist tether were hooked to the active astronaut's suit making a loop. The active spacewalker then put his arm through the loop to pull the incapacitated crew member along with both hands free.

"Man, that's a job I wouldn't want to have all day," Jones radioed after his two runs as active astronaut.

"What do you think about the difference between those two?" pilot Mark Polansky asked.

"Well, one difference is the single waist tether doesn't provide enough clearance from the crew member," Jones said. "In other words, he can get too close to you and you can't really move with any freedom."

The spacewalkers then disconnected, floated to the far end of the cargo bay and did it again, this time with Curbeam as the rescuer, using the strap method, and Thomas as the incapacitated astronaut.

"OK, nice and slow," Curbeam said to himself as he started towing Jones toward the airlock.

"I think I'll be a dead guy with a camera here," Jones said, snapping pictures with a 35 mm camera as he was pulled along.

"I can tell you already it's much harder to control his body position with the strap method," Curbeam radioed a moment later.

"The daisy chain keeps you out free and floating clear," Jones said.

"Yeah, you can control the incapacitated crew member's body position much better with the daisy chain. This method is much more difficult."

"We can see that just by watching," Polansky said from inside Atlantis' crew cabin.

"Yeah, and I'm working a heck of a lot harder on this run than I was on the last one, much harder," Curbeam said. "Plus you're not really tethered to him, you've got to watch out for the strap. ... And also I'm just afraid of losing him the whole time."