NASA works up plan for a risky spacewalk

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 E. Parazynski runs the risk of being shocked while 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 guide wire or guide wire 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 any metal on a tool he was holding touched it, the metal could melt and burn a hole in 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 and other tools.

Astronaut David Wolf, who heads the spacewalking branch in Houston, acknowledged that it’s possible -- although extremely unlikely -- that Parazynski could be electrocuted. They’ve done everything reasonable to keep that from happening, he added.