Endeavour Astronauts Inspect Shuttle Heat Shield Damage

This story was updated at 1:46 p.m. EDT (1736 GMT).

HOUSTON -- Astronauts aboard NASA's space shuttle Endeavour took a close look at a gouge on the underbelly of their orbiter Sunday while mission managers discussed whether to add a few extra days to their flight to the International Space Station (ISS).

"The primary thing that we're going to look for is how deep it is," John Shannon, chairman of Endeavour's STS-118 mission management team, said of the damage during a Saturday briefing here at NASA's Johnson Space Center.

A piece of foam insulation about the size of a grapefruit fell from a bracket on Endeavour's external tank and bounced off a metal strut to damage the belly-mounted tiles during the orbiter's Aug. 8 launch. Radar images caught a spray of debris and possible ice reminiscent of that seen during the debris hit that led to NASA's 2003 Columbia accident, but Shannon said the event was much less severe than that which afflicted Columbia.

The gouge, which is about 3 1/2 inches (about nine centimeters) and just over two inches (five centimeters) long, sits about four feet (1.2 meters) behind Endeavour's starboard landing gear door. The tiles in that area are just over an inch (2.5 centimeters) thick, but the precise depth of the damage site will be determined during today's inspection using a laser scanning tool at the end of a 50-foot (15-meter) extension to Endeavour's own robotic arm.

A closer look

During today's heat shield survey, STS-118 mission specialists Tracy Caldwell and Barbara Morgan - a former Idaho schoolteacher-turned-astronaut - used Endeavour's 50-foot (15-meter) robotic arm to grapple its inspection boom and scan five spots along the shuttle's hard-to-reach underside. Shuttle commander Scott Kelly aided in the activity, NASA said.

In addition to the damaged tile, Caldwell and Morgan were to inspect three other dings caused by the foam debris, as well as a piece of frayed fabric near Endeavour's main landing gear door during their three-hour survey.

The inspection began just before 12:00 p.m. EDT (1600 GMT) after Endeavour's robotic arm took its extension boom from the clutches of the space station's own robotic appendage. The shuttle's arm cannot grab the boom directly while Endeavour is docked at the ISS due to clearance issues with station hardware.

NASA called for the focused inspection on Friday after a photographic survey of Endeavour's heat shield performed by the space station's Expedition 15 crew before docking. The new images and data will help determine whether the damage tile will require a spacewalk repair, mission managers said.

Shannon added late Saturday, however, that the chance of sending an astronaut to repair the tile by coating it with either a protective paint, heat-resistant cover or filling it with a goo-like filler material is unlikely based on the current data.

NASA has kept a close watch on the integrity of shuttle heat shields since the tragic loss of the Columbia orbiter and its seven-astronaut crew in 2003. A 1.67-pound (0.75-kilogram) piece of foam damaged that orbiter's left wing-mounted heat shield at launch, leading to its destruction during reentry.

While shuttle astronauts inspect Endeavour's heat shield, the ISS crew continued a 28-hour repair job to replace corroded cables and an electronics box that led to a Russian computer crash in June. Expedition 15 commander Fyodor Yurchikhin and Oleg Kotov worked to mop up condensation behind panels containing the cables they were replacing.

Meanwhile, NASA engineers recovered a primary U.S. command computer aboard the ISS that shut down unexpectedly during a Saturday spacewalk, apparently due to a software glitch. The glitch had no impact on ISS or spacewalk operations, and the computer's two backups kicked in as planned, mission managers said.

"Last night we did power cycle it and reconfigured all of those computers so they were in a good state for today's operations," ISS flight director Heather Rarick said in a Sunday morning update.

Possible mission extension

While Endeavour's crew inspects the shuttle's heat shield, mission managers on Earth will discuss whether to extend the STS-118 spaceflight by three extra days based on the performance of a new Station-to-Shuttle Power Transfer System.

Endeavour astronauts successfully activated the new system after docking at the ISS on Friday, which allows the orbiter to draw on the station's solar power grid rather than its own fuel cell resources.

"It's a long extension cord with some power converts to convert the space station voltages to the voltage that the shuttle can use," Kelly said before flight.

The drop in fuel cell use led one of the three aboard Endeavour to grow colder than usual overnight, sounding an alarm that awoke the STS-118 crew. Fight controllers adjusted settings on acceptable fuel cell temperatures to avoid repeat alarms, NASA said.

Endeavour's construction mission to the ISS was initially slated to run 11 days and include three spacewalks to deliver a new starboard segment of the station, a spare parts platform and about 5,000 pounds (2,267 kilograms) of cargo for the orbital laboratory's crew. The three-day extension would mark a record 10-day stay at the ISS for a shuttle and allow the STS-118 crew to perform an extra, fourth spacewalk to support station construction, NASA has said.

Joel Montalbano, lead ISS flight director for Endeavour's flight, said the new system has been performing continuously since its Friday activation.

"That power transfer is doing fantastic," he added.

NASA is broadcasting Endeavour's STS-118 mission live on NASA TV. Click here for mission updates and SPACE.com's NASA TV feed.

• VIDEO: STS-118 Mission Profile: Station-to-Shuttle Power Transfer
• VIDEO: Teaching the Future: Teacher-Astronaut Barbara Morgan
• Complete Space Shuttle Mission Coverage