Cape Canaveral, Fla. Astronauts in orbit and engineers on Earth tried to figure out Thursday how best to pull off what will be one of the most difficult and dangerous spacewalking repairs ever attempted in orbit.
Spacewalker Scott Parazynski runs the risk of being shocked while he's trying to fix a ripped solar wing at the international space station. He'll attempt the job as early as Saturday.
NASA had hoped to send Parazynski out today, but needed more time to come up with a safe plan. If too many loose ends remain, the spacewalk would probably be bumped to Sunday, said flight director Derek Hassmann.
"We'll be ready to go in a couple days from now," Parazynski said Thursday.
Saving the ripped wing has become the top priority for what remains of shuttle Discovery's visit to the space station. Everything was going well until the astronauts discovered steel shavings inside a rotary joint for another set of solar wings. Then one of the wings on a beam that had just been relocated on the space station tore in two places.
Engineers believe the 115-foot wing snagged on a guidewire or guidewire support as it was being unreeled Tuesday. Until Parazynski gets close to the damage, NASA does not know what he'll need to do to fix it.
The partially unfurled solar wing is producing power, and there is no way to turn it off, Hassmann said. Flight controllers have already warned Parazynski not to touch the electricity-generating solar cells that cover virtually the entire wing. If the metal of a tool he was holding melted, it could burn a hole into his glove.
"Just a kind of small slip and you could be touching it," said Dina Contella, the lead spacewalk officer in Mission Control.
The metal parts of Parazynski's spacesuit will be covered with insulating tape, as will his wire cutters, pliers and other tools.
Astronaut David Wolf, who heads the spacewalking branch in Houston, acknowledged that it's conceivable - although extremely unlikely - that Parazynski could be electrocuted. They've done everything reasonable to keep that from happening, he added.
One of the biggest challenges was devising a way to get Parazynski to the damaged section of the wing.
Working by remote control from inside, the astronauts will attach the space station's 58-foot robot arm to the center of the 50-foot boom that was carried up by Discovery to inspect the shuttle's thermal shielding for any launch damage. Parazynski will step onto an extension added to one end of the boom.
Mission Control expects it will take between 30 and 60 minutes for Parazynski to reach the damaged area. NASA normally likes to keep spacewalkers no more than 30 minutes away from the cabin hatch in case of an emergency.
Wolf said that won't be the case this time, but it's unavoidable because the space station needs the repair.
Wolf said he expects the repair to be as difficult as the work on the Hubble Space Telescope. But he noted that those spacewalks were rehearsed extensively before the flights and, in this case, Parazynski will be attempting something that was conceived just in the past few days.
NASA says the ripped wing needs to be fixed or the solar rotary joint problem solved before any more shuttles can fly to the space station and continue construction.