NASA was assessing damage found Tuesday on the underside of the shuttle Atlantis, but downplayed any threat to the astronauts or their mission as the craft raced toward a risky high-orbit rendezvous with the Hubble telescope.
The US space shuttle Atlantis lifts off May 11, 2009 at Kennedy Space Center in Florida on the final shuttle mission to service NASA's Hubble Space Telescope. (AFP Photo)
During a marathon 10-hour survey of fragile heat shielding, the seven member Atlantis crew found a string of gouges stretching 53 centimeters (21 inches) across four heatshield tiles on the underside of the forward portion of the shuttle's right wing sustained during the craft's launch into orbit.
The US space agency characterized the damage, which will undergo at least two days of evaluation by imagery experts in Mission Control, as minor.
"The same amount of damage in another area might be more critical," LeRoy Cain, who chairs the NASA mission management team, told a news briefing. "The damage itself appears to be relatively shallow, and it's not a very large area."
Mission Control ruled out the need for a second and more focused inspection of the damage site on Friday, freeing up more time for Hubble's overhaul.
"The preliminary assessment is that it does not look too serious," shuttle communicator Dan Burbank told Atlantis Commander Scott Altman from Mission Control.
Atlantis lifted off with seven astronauts on Monday, initiating an 11-day day mission to give the 19-year-old Hubble Space Telescope an optical makeover, equipping the observatory to carry on operations for at least another five years.
The shuttle crew was on course to rendezvous with the 560-kilometer (350-mile) high galactic observatory on Wednesday shortly after noon.
In what will be a nail-biting operation, Altman will steer his ship close to Hubble, as astronaut Megan McArthur reaches out with the shuttle's robot arm to grab the 13.2-meter (44-foot) long telescope.
With the observatory in the arm's grasp, McArthur will mount the telescope upright atop a circular platform in the shuttle's cargo bay, establishing the work site for the overhaul.
The first of five grueling hours-long spacewalks by the astronauts to upgrade the observatory will then get under way Thursday.
During the mission, the spacewalkers aim to install a pair of new science instruments and make unprecedented repairs to the electronic circuitry within an older camera and spectrometer.
NASA experts believe the damage to the shuttle may have occurred about 103 seconds into the space craft's climb to orbit, the time at which a sensor in the right wing recorded an impact, Burbank said.
Neither the source nor the size and mass of the debris had been identified, but NASA said a camera positioned on the underside of Atlantis and aimed at the shuttle's external fuel tank may have recorded the source of the impact debris.
However, a power cable problem prevented the astronauts from retrieving and transmitting the electronic imagery to Mission Control following the launch, and they were to make another attempt to retrieve the photos later Tuesday.
NASA has characterized the mission as riskier than the dozen shuttle visits to the International Space Station (ISS) since the 2003 Columbia tragedy that claimed the lives of seven astronauts.
That disaster was blamed on an undetected breach of the protective heat shields caused by a launch day collision with a breakaway chunk of foam fuel tank insulation.
In the aftermath of the explosion, NASA made heat shield inspections a part of every mission and made plans to mount a rescue mission if the astronauts on future missions found damage that could not be repaired.
Circling Earth much higher than the space station, Hubble is exposed to an accumulation of space debris from a satellite collision earlier this year as well as the fragments left from previous spacecraft breakups.
While the space station offers weeks of refuge for the crew of a stricken shuttle, Hubble is not equipped to house astronauts.
To address that concern, NASA has readied another shuttle, the Endeavour, for an emergency rescue mission if need be.
"We have not seen anything in our early assessments that makes us think that in any way will be necessary," said Cain.