NASA hatches daunting solar wing repair plan

Blogger note: Click to enlarge and save the NASA TV screen shot above. The torn solar blanket is on the outboard set of solar wings, and this photo gives you an idea about the challenges involved with getting a spacewalker to the repair site.

In what will be an unprecedented orbital fix-it attempt, a spacewalking astronaut will try to save a damaged International Space Station solar wing this week by mending a torn blanket while anchored to a makeshift scaffold.

Discovery mission specialist Scott Parazynski will attempt to stitch up a ripped and rippled section with a series of up to seven straps -- restoring full structural integrity to the solar wing while preventing further damage.

Made of lengthy wires with tabs attached either end, the straps will be strung through existing, reinforced holes that are spaced evenly across the 15-foot width of the blanket. The holes were designed for lengthy pins that secured folded up blanket panels in the rectangular boxes they were launched in.

A snagged guidewire that caused the tear will be severed first. Parazynski will be nachored to an orbital inspection boom fixed to the end of the station's robot arm while he is doing the work.

Perched atop a mobile rail cart, the station's 57.5-foot robot arm will snatch up a 50-foot orbital inspection boom now stowed on the starboard sill of shuttle Discovery's cargo bay.

The station crane will take hold of a grapple fixture at the midway down the length of the boom. The crane routinely lifts the boom from the shuttle's cargo bay because the shuttle's robot arm cannot reach it when docked at the station. The U.S. Destiny lab is in the way.

Then the rail cart will be rolled along tracks to a work station near the far left end of the central truss.

What amounts to a 25-foot extension of the station's robot arm will enable Parazynski to reach the damaged area of the blanket without having to retract it. That's important because engineers fear the tear would rip further if the array is extended or retracted before the repair work is done.

Discovery mission specialist Douglas Wheelock will assist Parazynski on the spacewalk. Italian astronaut Paolo Nespoli of the European Space Agency will direct the work from inside the shuttle-station complex. Station flight engineer Dan Tani will be the prime station arm operator.

A 2 1/2-foot long tear and another smaller rip were spotted when the blanket was being unfurled at the station. The joined shuttle and station crews aborted the deployment operation.

NASA program managers scrapped plans to send Parazynski and Wheelock on a planned spacewalk Thursday to inspect a foul-up rotary joint on a separate solar wing set on the starboard end of the station's girder-like central truss. They deemed the effort to repair the solar blanket a higher priority.

The planned fifth spacewalk of the mission -- one aimed at external outfitting of the newly arrived U.S. Harmony module -- will be conducted by commander Peggy Whitson and flight engineer Yuri Malenchenko after Discovery departs the station.

A fifth spacewalk on Sunday to finish solar blanket repair work is an option.

NASA still plans to launch Atlantis and the European Columbus science laboratory to the station on Dec. 6.