Cape Canaveral, Nov 3: NASA has planned for the worst in a risky, high-stakes spacewalk today that must succeed for construction to continue aboard the International Space Station, officials said.
But managers are hoping three days of around-the-clock engineering assessments, private talks with the orbiting shuttle and space station crews and the detailed plans to send a spacewalker to the far outer reaches of the station will boil down to a simple, 30-minute wiring job to buttress broken hinges on a damaged solar wing panel.
''It's a snag clear. It's not rocket science,'' lead spacewalk planner Dina Contella said.
Though he is one of NASA's most experienced spacewalkers, astronaut Scott Parazynski has not practiced the steps he must take to clear suspected jammed wiring and other hardware glitches that caused the wing to rip in two places while it was being extended on Tuesday.
NASA had not planned for that possibility, nor a second problem, which has been temporarily postponed, with the solar power system on the other side of the station's frame. That wing is now locked in place to avoid using its contaminated rotary joint.
The ripped wing is about 75 percent unfurled and needs to be extended to its full 110-foot-(34-metre) long span for structural rigidity. Without that, NASA said it will not risk adding more modules to the outpost. Europe's Columbus laboratory, already running five years behind schedule, is next in line for launch, followed by Japan's three-part Kibo complex next year.
''At this point we have damage at both ends of the truss,'' said space station flight director Derek Hassmann. ''We need to address one of these problems before we can proceed.'' DAUNTING TASK Choreographing a spacewalk that will put an astronaut farther from his spaceship than ever before was a daunting task that has preoccupied the Johnson Space Center flight control team since Tuesday.
To reach the tattered wing, Parazynski will strap himself to the end of an extension boom, borrowed from the space shuttle, that will be held by the space station's 50-foot(15-metre) -long robot arm, providing about 75 feet (23 metres) of reach. Just the ride to the work site will take 45 minutes, Contella said.
Once in position, Parazynski will be dependent on his spacewalking partner, Douglas Wheelock, to warn him of danger, watch his tools and tethers and help robot arm operators in the space station position him correctly.
NASA likes to keep its spacewalkers closer to the airlock in case they have to return quickly due to a spacesuit problem or other emergency. Fixing the station's broken wing, however, will cut into that margin of safety.
Parazynski also must be careful to avoid touching anything that could trigger an electrical shock. His tools and even the metal rings on his spacesuit have been wrapped in insulating tape but ''we're treating the situation as if there are hot wires that he could possibly contact,'' Hassmann said.
If all goes well, Parazynski will install six home-made straps that fit like cuff links through holes in the solar power wing's frame.
Hassmann said his team's advice to the crew: ''Go slow, be careful and use all your resources.
NASA is sketching out a backup plan to extend Discovery's stay at the station in case a second repair spacewalk is needed. The shuttle arrived at the station eight days ago and is slated to depart on Monday.
''I have hopes it's going to be a quick and easy fix,'' Hassmann said. The shuttle is due back at the Kennedy Space Center in Florida on Wednesday.