HOUSTON -- Two astronauts will venture outside the International Space Station today to dangle from the end of a 100-foot pole that could be used to make repairs to the heat shield of the space shuttle Discovery, which is docked to the station.
Piers Sellers and Mike Fossum are scheduled to begin their planned 6 1/2 -hour excursion outside the spacecraft, which is docked to the International Space Station, about 9:15 a.m.
In addition to performing maintenance on the station, the astronauts will conduct a test by alternately standing in foot restraints at the end of a boom held by shuttle Discovery's robotic arm.
The boom and the arm are each 50 feet long. The test will determine whether the joined sections flex and sway too much to support an astronaut doing repair work.
Sellers likened the exercise to standing on the end of a long telephone pole 200 miles above the Earth.
"At night, you'll feel either that you are standing on a diving board or standing on top of a telephone pole or hanging down from something suspended from the ceiling," Sellers said in an interview before Tuesday's shuttle launch. "It's potentially disorienting, there's no question."
"We've thought about that and tried to train for that. We probably won't always know which way is up. We're going to focus on the only structure we have, which is the end of the pole."
Sellers and Fossum might get a chance to use the procedure in earnest if NASA decides to pull out a gap filler sticking up an inch from between heat-resistant tiles on the shuttle's belly.
After a follow-up inspection of six spots on Discovery's heat shield yesterday, engineers are further analyzing three areas before declaring the shuttle safe to come home. Two are small nicks in the thermal panels that cover the leading edges of Discovery's wings. Another is the gap filler near Discovery's tail, beside a door where the shuttle connects to its external fuel tank.
Engineers are expected to decide this weekend whether a similar fix is required on this flight.
"The one [analysis] we'll take some time on is the gap filler," said Steve Poulos, manager of NASA's orbiter project office. "The reason we'll take time on it is the height of the protrusion."
If the gap filler is removed, it will probably be done during a third spacewalk planned for Wednesday. The spacewalk was added when mission managers decided yesterday to add a day to Discovery's flight. The added spacewalk will focus on testing materials that could be used in orbit to repair the shuttle's heat shield.
The shuttle's new scheduled landing time at the Kennedy Space Center in Florida is 9:07 a.m. July 17.
In orbit yesterday, astronauts attached a cylindrical cargo module named Leonardo to a port on the station. The shuttle and station crews will spend the next six days unloading about 5,100 pounds of supplies and science equipment from the Italian-built container.
"It's really quite a challenge because you're in zero-G [weightlessness]," Discovery commander Steve Lindsey said. "You've got to go very, very slow. If you go fast, you tend to run into things."
Michael Cabbage writes for the Los Angeles Times.