NASA Reveals Plan to Fix Solar Wing
An view of damage to the International Space Station's 4B solar array, located on the Port 6 truss, that occurred on Oct. 30, 3007. A revised spacewalk isplanned to free the tangled solar wing and make repairs.
Credit: NASA

HOUSTON - NASA revealed unprecedented spacewalking plans today that could mend a maimed solar wing at a far end of the International Space Station (ISS) on Saturday.

The space agency said astronauts will attempt to repair the working power-generating solar array, which partially tore at its hinges during deployment on Oct. 30. Mission managers indicated most details are set for the spacewalk, but gave themselves a 1:08 a.m. ET (0508 GMT) deadline early Friday to ship complete instructions up to astronauts.

"We're faced with a difficult situation," said David Wolf, head of the EVA branch for the astronaut office, here at Johnson Space Center. "I think we're onto a solution that should work and get us pretty close to a permanently acceptable situation."

The extravehicular activity, or EVA, will send STS-120 astronaut Scott Parazynski on a one-hour ride on an extended robotic arm to the damage site while fellow astronaut Doug Wheelock looks on. Donning protective goggles, astronauts in space worked today to craft "cuff links" that should button up the 2.5-foot (0.76-meter) tear in the array.

If Parazynski does not effect a repair from his 90-foot-long (27-meter-long) robotic ride, mission managers said spacewalkers could try again on a following day.

Derek Hassmann, ISS lead flight director for the STS-120 mission, said teams are still working around the clock to get the complete details together for the fourth spacewalk. Management teams delayed the EVA to Saturday to buy more time.

"We knew it would be a full-court press to get there on Friday, and I'm disappointed that we didn't get there," Hassmann said. "But I'm satisfied we made a good call."

Tricky choreography

Engineers who scrutinized solar array photographs think a piano-wire-like guide line caught on a hinge of the 4B solar array, unzipping it along the way. The solar wing was deployed about 80 percent before astronauts on board the space station aborted the operation.

Lead STS-120 spacewalk officer Dina Contella said two tears--one large and one small--might be somehow related to the cable.

"We know that there's a snag there, but we're not sure ? if it's something really easy to clear," Contella said, noting that Parazynski will be toting a pack of tools to work with.

Whatever the case, Parazynski will get an up-close-and-personal look at the damage?at which time flight controllers will huddle to decide what steps to take next.

"When Scott is out there with his helmet cameras right at the repair (site), that will be our first really close look at this problem," Wolf said. "we're going to have to as a team ? quickly develop a plan of action."

Shocking danger?

Hassmann said the EVA carries a risk of electric shock via the 110 volts coursing through one part of the solar wing, which generates about 13.4 horsepower (that of medium-sized backup generator).

"Once [solar arrays] are deployed, they start producing power as they're designed to do," Hassmann said of the 110-foot (33.5-meter) sail of solar cells. "There's nothing we can safe or turn off the array while it's deployed."

But mission managers noted that any extra risks they may place Parazynski under during the 6.5-hour EVA will be under control.

"Our job is to think of all those possible ways where a bad outcome could occur ? and be sure that every hazard is mitigated and handled," Wolf said. "We can come up with hazards, including electrocution--and thus we are sure that we have mitigated that hazard within any reasonable means."

The STS-120 space station construction mission launched with the space shuttle Discovery on Oct. 23 and is slated to depart the space station on Nov. 5 for a Nov. 7 daylight landing. There are enough supplies on board the spacecraft to extend the already extended mission by another two days, if necessary.