NASA ordered Endeavour's crew to take an unusual close-up look at a damaged tile in the space shuttle's delicate heat shield early Saturday morning.
Using the shuttle's robotic arm, astronauts will scrutinize the gouge on the shuttle's underbelly with a high resolution camera and a laser attached to a boom.
"There's nothing alarming here and we're not really concerned," said LeRoy Cain, chairman of the shuttle mission management team that decided Friday to order what's called a "focused inspection."
Cain said the two-hour maneuver is being done out of an abundance of caution and won't cause any disruption to the crew or its 16-day mission to the International Space Station.The damaged tile was spotted in photos snapped by the station crew just before the shuttle linked up Wednesday. Initially, the photos showed seven sites with dings or gouges, but six of them were further analyzed and turned out not to be a problem.
The one site that remains a concern is the size of a deck of cards, just below the rear landing gear.
The location and size gives engineers a bit of confidence that the damage is not the type that caused the disintegration of the space shuttle Columbia in 2003. They also note that similar damage on Endeavour in 2007 -- coincidentally commanded by Scott Kelly, brother of current commander Mark Kelly -- turned out not to be a problem.
Cain told reporters that it's so unlikely that the gouge will be problematic that NASA hasn't even considered making contingency plans for fixing the tile in flight. NASA can repair damaged tiles using a souped-up version of a caulking gun during a spacewalk.
The delicate tiles are part of an intricate heat protection system that keeps the shuttle, especially its bottom and edges, from burning up during its fiery re-entry into Earth's atmosphere. In 2003, damage to the edges and tiles allowed too much heat in, destroying Columbia and killing seven astronauts.
Since then, shuttles have been checked in flight for any ice or foam debris damage from liftoff, to make sure the shuttle is safe to fly home. This is only the fifth time an extra inspection has been needed in 21 flights.
For Saturday's inspection, the camera will take just three close-up photos from 7 feet away and the laser will get two sets of data. Officials expect that will be enough information to plug into computer models to assure them that the damage isn't anything to be worried about.
This is Endeavour's last flight and the second last of the 30-year space shuttle program. NASA is shutting down the program to focus on eventual missions to a nearby asteroid or other places further out than Earth's orbit. Shuttle Atlantis is tentatively set to make the last flight on July 8 with a load of supplies and equipment for the station.
Friday turned out to be a day of small concerns for NASA, after an early morning routine spacewalk had to be cut a tad short because of a sensor problem on an astronaut's spacesuit.
Nearly five hours into the 6 1/2-hour spacewalk, mission controllers noticed that Gregory Chamitoff's carbon dioxide sensor wasn't working. NASA needs to know if levels of carbon dioxide -- expelled when you breathe -- get too high.
It's likely that moisture caused the infrared sensor to fail, said lead spacewalk officer Allison Bolinger.
The levels were probably not too high, but controllers told Chamitoff and spacewalking partner Drew Feustel not to finish installing an antenna on the space station because it would take too much time.
In the end, the spacewalk was 11 minutes shorter than planned. Feustel and Chamitoff installed a light fixture and swapped out some experiments parked outside the space station.
This was the first spacewalk for Chamitoff. He called it "a dream come true for me."
Endeavour's astronauts will make four spacewalks while docked at the space station.
NASA approved a first-of-its-kind maneuver on Monday for a photo op when a Russian Soyuz capsule undocks from the space station with three astronauts aboard. The capsule will back away to about 600 feet and stop. Then the station will slowly rotate so the Soyuz can get rare photos of the shuttle docked to the station from different angles and from another spaceship.
Delivered by Endeavour and added to the space station on Thursday was a $2 billion physics experiment that looks for antimatter and dark matter. Saturday, the two crews will get an unprecedented VIP call -- Pope Benedict XVI will make the first papal call to space.