Discovery astronauts wrap final spacewalk

Shuttle astronauts finished another day of work on the International Space Station and tested out spacewalking rescue techniques

October 18, 2000
Web posted at: 6:34 p.m. EDT (2234 GMT)

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From Miles O'Brien
CNN Space Correspondent

(CNN) -- On the fourth -- and final -- spacewalk of the 100th space shuttle mission, a pair of NASA astronauts "cleared the decks" for what they hope will happen next at the budding International Space Station. They also tested a new jetpack sytem designed for space station use.

Spacewalkers Mike Lopez-Alegria and Jeff Wisoff wrapped up a seven hour day the weightless work site at about 6 p.m. EDT. They and crewmates Bill McArthur and Leroy Chiao had already logged three full days of work attaching two major components to the International Space Station -- along with assorted cables, connectors and boxes that will link the new pieces to the orbiting outpost.

Lopez-Alegria and Wisoff worked their way through the busy timeline with only a few hitches.

"You guys are looking great, you are right on the timeline," said McArthur, serving as the spacewalk choreographer and taskmaster on the aft flight deck of the shuttle Discovery.

But it wasn't problem-free. Once again, the pair had some problems with their high-tech cordless drills (Pistol Grip Tools, or PGTs in the NASA vernacular).

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"Sounds like that is a flaky PGT," McArthur said. But as it turns out, the warning lights were blazing up on more than one of the power tools. For now, the problems remain a mystery.

The spacewalkers also used their PGTs to test the latches that will grab the next big piece of the station due for delivery. The so called P-6 truss will be hauled to orbit inside the payload bay of the next shuttle in line: the good ship Endeavour. She is expected to launch November 30.

They also attached a cable "tray" to the exterior of the station that will make it possible to connect the U.S. Laboratory "Destiny" to space station systems.

Toward the end of their six-and-half hour shift, the pair tried out some techniques that could one day get them -- or some of their spacewalking colleagues -- out of a life-threatening jam.

Spacewalkers obey a strict "double tether" rule -- meaning they are always attached to either the shuttle or the space station, even as they move long distances away from the airlock. Rock climbers who are familiar with the rules of being "lead" will instantly understand the regimen.

Commander Brian Duffy uses an I-Max camera to film his crew on Discovery's middeck after a 6-hour-plus spacewalk

But should a spacewalker break free, what are the options? Better than those of rock climbers in most cases, but not all. On a walk outside the shuttle, the commander could simply maneuver the orbiter to save a drifting astronaut. But during spacewalks outside the station, that safety net won't be there, since the hulking station is just not nimble enough.

So NASA has been testing a device called the Simplified Aid for EVA Rescue (or SAFER -- EVA stands for Extravehicular Activity), a small thruster that attaches to a spacewalker's backpack. SAFER is purposely designed to be as small and unobtrusive as possible. But is it too small to do the job? That is the question of the moment.

"We found a couple of undesirable aspects of the hardware," said the dean of the U.S. spacewalking corps, Jerry Ross. Ross found those problems when he tested the SAFER device on the first shuttle mission to the space station in December of 1998.

Ross says the problems have been fixed, but he adds: "In simulations, we can get in situations where we don't have enough thrust capacity to rescue ourselves." So the testing goes on.

Because tool problems slowed their space station work, the astronauts ran out of time and had to skip the final test: lugging one another to demonstrate what it would be like to rescue an incapacitated spacewalker.

Of course, today, the spacewalkers had the luxury of worrying about less-serious matters.

"Why didn't they incorporate foot heaters in the (spacesuits)?" wondered Lopez-Alegria at one point.

The next key piece of the station due to arrive -- the P-6 truss -- includes the first set of U.S. solar arrays, able to provide enough power to keep the U.S. Laboratory Destiny up and running. Destiny now sits inside the cavernous clean room at the Space Shuttle Processing Facility at the Cape.

Bunny-clad technicians are working feverishly to finish it on time. Destiny has a non-refundable ticket to ride on Atlantis on January 18.

Sources said the lab, which is the heart and soul of the U.S. side of the station, is destined to be on time, but by the slimmest of margins. A series of hoses that carry ammonia in and out of the module for cooling are giving engineers fits right now. The quick-disconnect devices were not designed very well, and some O-rings are failing once the hoses are disconnected. It has caused some ammonia leaks in ground tests, but NASA may have to live with this problem and hope for the best -- for now.

It is hard to comprehend how many brand new systems, components and widgets will be linked together on the U.S. side of the shop. In and of itself, making all of these things work on their own -- and then in harmony with each other -- is a mind-boggling engineering challenge.

Add to that the complexities of working with the Russians and you begin to understand why a lot of people say Apollo was a logistical piece of cake by comparison.

Third spacewalk complete; power converters installed
October 17, 2000
Two spacewalks down; two new pieces in place on space station
October 16, 2000
Discovery docks at International Space Station
October 13, 2000
Shuttle Discovery zooms in on orbiting outpost
October 12, 2000
Shuttle soars into space for 100th time
October 11, 2000
NASA scrubs 3rd attempt to launch shuttle
October 10, 2000

Shuttle Orbiter Discovery (OV-103)
NASA
Human Space Flight (HSF) - International Space Station

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