Third Spacewalk Planned for Shuttle Crew

Analysts have identified a second gap filler protruding from the heat tiles along Discovery's belly after its STS-121 launch on July 4, 2006. The gap filler is located in the aft, near the body flap. CREDIT: NASA.

HOUSTON - NASA mission controllers are planning a third spacewalk and an extra day in space for six astronauts aboard the shuttle Discovery, the orbiter's lead flight director said Friday.

"It's a done deal," said Tony Ceccacci, lead shuttle flight director for Discovery's STS-121 mission, adding that the decision will be finalized later today. "We're going to tell them we'll step up to do a 13-day mission and we'll plan accordingly."

The extra day will allow STS-121 spacewalkers Piers Sellers and Michael Fossum a chance to test additional crack repair methods in the reinforced carbon carbon panels that line the shuttle wing leading edges, Ceccacci said during a mission briefing here at NASA's Johnson Space Center.

A third spacewalk was originally in the mission plan for Discovery's STS-121 spaceflight, but was pulled off the docket in May due to the flight's busy schedule. Sellers and Fossum continued training for the extravehicular activity anyway, banking on the assumption - since proven - that the supply of cryogenic liquid hydrogen and liquid oxygen that powers Discovery's fuel cells could last an extra day in orbit.

Ceccacci said the extra mission day also gives Discovery's crew some leeway in terms of cargo transfer. The day could also be used to make heat shield repairs on the off chance that today's focused inspections of Discovery turned up a last-minute issue, such as the need to pluck a pair of gap fillers from between the spacecraft's belly-mounted tiles, he added.

"There are some concerns and that's why we're doing the focused inspections," Ceccacci said.

NASA set aside four hours today for the STS-121 crew to examine six different concerns; a gap filler jutting out near Discovery's starboard external tank door, a gap filler - dubbed "tadpole" - along the forward section of the orbiter, a white spot that appears similar to bird droppings on the nose cap, two scuffs on a right wing RCC panel and a dark spot on another RCC panel on the same wing.

Focused inspections began about one hour late due to questions over the clearance requirements when handling Discovery's orbital boom, which is a 50-foot (15-meter) extension of its 50-foot (15-meter) robotic arm, near the ISS, Ceccacci said.

Meanwhile, Sellers and Fossum are preparing for the first spacewalk of their mission. The two spacewalkers are set to make repairs to a cutting system used on the station's railcar-like Mobile Transporter and to test the stability of the orbital boom as a work platform.

That spacewalk will begin at 9:13 a.m. EDT (1313 GMT) and be broadcast live on NASA TV.

• Gallery: Shuttle's First Flight
• Gallery: Rare Space Shuttle Images
• Shuttle Discovery: Complete Mission Coverage
• Great Space Quizzes: Space Shuttle Countdown
• Great Space Quizzes: The Space Shuttle
• Great Space Quizzes: Life in Orbit