By Todd Halvorson CAPE CANAVERAL, Fla. Shuttle Discoverys astronauts stole a chapter out of a Buck Rogers book Wednesday, test-flying jet backpacks that one day might save construction workers cast adrift from the
International Space Station.In what amounted to a slow-motion emergency drill, spacewalkers Jeff
Wisoff and Michael Lopez-Alegria took the gas-powered jetpacks for a spin in the shuttles cargo bay. 
Astronaut Jeff Wisoff tests the jet backpack that can be used to rescue wayward spacewalkers.
Floating high above their mother ship, the astronauts zoomed down to the edge of the bay, mimicking the type of flight spacewalkers would face if they accidentally tumbled off into the deadly vacuum of space.
"That was way too much fun," Lopez-Alegria said.
Added Wisoff: "Can I go again?"
Coming amid NASAs most ambitious station construction mission to date, the jetpack tests were the highlight of the fourth and final
spacewalk planned for the agencys 100th shuttle flight.A second rescue drill one aimed at seeing whether an unconscious astronaut could be hauled back to the shuttle for medical attention was called off due to a lack of time. More critical mop-up work with a newly installed station truss took longer than expected.
Wisoff made the first test run, starting out at a point 50 feet (15 meters) above Discoverys payload bay. Anchored to the end of the shuttles lengthy robot arm, Lopez-Alegria remained nearby, playing out Wisoffs standard safety tethers like fishing line.
Made of braided-steel, the tethers always are worn as a precaution during spacewalks. They are even more critical when a shuttle is parked at the station, because the ship then cannot quickly undock and chase after an astronaut in an emergency.
"I certainly feel like Mike is my best friend in the world right at the moment," Wisoff said as Lopez-Alegria kept tight control of his tethers. "Hes my only friend in the world right at the moment."
"Is it worth a bottle of Chateau Margeaux?" Lopez-Alegria chimed in.
"I guess so," Wisoff said.
Added Lopez-Alegria: "Im not kidding."
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Following a highly choreographed test regime, Wisoff first flew around a small imaginary box to see how well the 85-pound (38.5-kilogram) jetpacks steered.
Powered by 24 nitrogen-gas thrusters, the rescue packs are controlled with hand-held joysticks a difficult task when trying to soar in place.
"This is kind of what we expected: Its kind of hard to hard to hover. Its not really designed for that," Wisoff told crew mate Bill McArthur, who was watching out shuttle flight deck windows.
"Well I dont think a helicopter pilot would have had a hovering problem," replied McArthur, who used to fly whirlybirds for the U.S. Army.
"I thought real men didnt hover," Lopez-Alegria, a naval aviator, added.
Astronauts Jeff Wisoff and Mike Lopez-Alegria prepare to test space rescue techniques at the International Space Station during the fourth spacewalk of STS-92 on October 18, 2000.
"Au contraire," McArthur said.
Pulsing the jetpacks tiny jet thrusters, Wisoff then flew slowly and deliberately toward his target a TV camera mounted in the rear of the shuttles cargo bay.
With Discovery flying on the dark side of Earth and helmet lights on Wisoffs spacesuit glaring brightly - the four-minute test-flight was quite a spectacle for the shuttle crew.
"Hey Jeff, that flight through darkness really looked cool, with your helmet headlights on," McArthur said.
"I cant believe what we just did," Wisoff said.
Lopez-Alegria then took his turn, and was equally awed by the experience.
"Oh, man, this is so frigging unbelievable," he said.
Both spacewalkers reported problems reading electronic displays on jetpack control panels, which are mounted on the front of their spacesuits. But overall, the two test pilots said the jetpacks worked pretty much as advertised.
"The task of flying straight, in my opinion, is much simpler than flying in a little box, because of all the hovering problems," Wisoff said. "But you know, its not designed to hover. Its designed to get you from point to point, and it did that task very well."
"You made it look easy," Chiao said.
The jetpack tests were carried out after Wisoff and Lopez-Alegria finished up their last outpost construction chore: "Clearing the deck" on the stations new rooftop truss, which was mounted to the 13-story outpost Saturday.
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That work involved removing a grapple fixture that enabled Japanese astronaut Koichi
Wakata to latch onto the truss with the shuttles robot arm and put it in place on one of three permanent wings that now make up the 80-ton station.Shaped like a round dish with a large pin protruding from it, the fixture was detached and stowed to make way for a pair of power-producing solar arrays to be delivered aboard shuttle Endeavour after a planned Nov. 30 launch.
The 9-ton truss will serve as a temporary mounting point for the giant solar panels, which will have a wingspan of 240 feet (73 meters) once unfurled in orbit.
The spacewalkers also swung open a square cable tray on the truss so that a future assembly crew can hook coolant lines to it. The ammonia lines will connect to radiators on the solar arrays, providing a means to shed heat generated by station electronics.
Astronauts Jeff Wisoff and Mike Lopez-Alegria test space rescue techniques at the International Space Station during the fourth spacewalk of STS-92 on October 18, 2000.
But the jetpack tests clearly provided the drama for the day.
"Jeff, whats it like being a satellite?" Chiao asked Wisoff midway through his test-flight.
"A human spacecraft
-- pretty awesome," the veteran spacewalker replied.With the quartet of back-to-back spacewalks now history, Discoverys astronauts will spend the day Thursday inside the station, delivering supplies for the outposts first full-time tenants.
The so-called Expedition One crew now is scheduled for launch from Baikonur Cosmodrome in Kazakhstan on October 31 a day later than planned.
The one-day slip will ensure the crew can rendezvous and dock with the station which was hauled into a slightly higher orbit by Discoverys crew after a planned two-day trip.
The shuttle astronauts, meanwhile, are scheduled to depart the station Friday, heading out on their own two-day trip back to Earth. Landing remains scheduled for 2:10 p.m. Eastern Daylight Time (18:10 GMT) Sunday here at Kennedy Space Center.
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