HOUSTON -- A chunk of foam insulation, not ice, damaged the protective belly-mounted tiles of NASA's space shuttle Endeavour during its launch earlier this week, mission managers said late Saturday.
Video recorded by cameras on Endeavour's twin solid rocket boosters during its Aug. 8 launch caught a grapefruit-sized piece of fuel tank foam as it gouged a 3-inch square (19 square centimeter) gash into heat-resistant tiles on the orbiter's undercarriage, said John Shannon, chair of NASA's shuttle mission management team.
"We feel like we have the culprit," Shannon said in a mission briefing here at NASA's Johnson Space Center. "I think we have conclusively shown where the piece of foam came from."
The foam piece fell from a lower bracket attaching a 17-inch (43-centimeter) liquid oxygen feed line to Endeavour's fuel tank about 58 seconds after liftoff, then bounced off a metal strut to bite into two of the black ceramic tiles near the shuttle's rear right landing gear door. In addition to the gouge, the foam debris caused a series of other scuffs aft of the initial impact, Shannon said.
"It was bad luck because we got a bad bounce off this [external tank] strut," he added.
Because the debris appears to be primarily made up of foam, and not denser ice as originally thought, mission managers are more confident that the damage inflicted is not be severe enough to require a spacewalk repair. But Shannon said Endeavour's astronaut crew will conduct an in-depth inspection of the tile damage Sunday to be sure.
"If we even have half the tile left, then we're not going to have any issues with this at all," Shannon said.
Initial computer modeling, based on the assumption that the foam hit gouged deep enough to reach close to Endeavour's aluminum skin, found that the orbiter could return to Earth as is in the event of an emergency, Shannon said. The damage site is also under a metal support strut, which would soak up excess heat if the underlying tile were compromised, he added.
NASA has kept a watchful eye on fuel tank foam debris and shuttle heat shield integrity since 2003, when an errant chunk of insulation breached the left wing of the space shuttle Columbia during launch. The resulting damage allowed superheated atmospheric gases into Columbia's left wing during reentry, leading to the loss of the orbiter and its seven-astronaut crew.
Since then, the space agency has redesigned shuttle fuel tanks to lower the amount of foam shed during launch and instituted mandatory in-orbit heat shield inspections for orbiter crews.
NASA has seen foam fall from the brackets along external tank liquid oxygen feed lines in the past, including on four of the last six shuttle missions since the agency returned its orbiter fleet to flight in 2005, Shannon said. The STS-26 flight in 1988, the first to fly after the 1986 Challenger accident, returned safely with similar damage as that seen on Endeavour, he added.
The space agency found that ice can form on the flexible liquid oxygen feed line as it is filled with the super-cold oxidizer, which is used along with liquid hydrogen to fuel a space shuttle's main engines during launch. The ice can later expand to pop out nearby foam insulation, causing debris.
"It's a little bit of a concern to us because this seems to be something that has happened frequently," Shannon said, adding that future tanks will rely on foam-less, titanium brackets beginning with the flight just before the September 2008 launch to service the Hubble Space Telescope.
In the meantime, the likelihood that a spacewalk repair will be required for Endeavour appears to be dwindling based on the new data, Shannon said.
"I would say that that is much more doubtful than it was yesterday," he added.
Commanded by veteran shuttle flyer Scott Kelly, Endeavour's STS-118 mission is delivering fresh cargo, spare parts and a new structural piece to the ISS. The mission also marks the first flight of teacher-turned-astronaut Barbara Morgan, who was selected as NASA's backup Teacher in Space in 1985 and will help perform Sunday's focused heat shield inspection.
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: Endeavour's STS-118 Mission Profile
- VIDEO: Teaching the Future: Teacher-Astronaut Barbara Morgan
- Complete Space Shuttle Mission Coverage