Space shuttle Atlantis has some nicks and scratches, but NASA says they're nothing to worry about.

The damage was probably incurred during liftoff Monday, when some debris came off the shuttle's external fuel tank.

A 21-inch stretch of nicks was found spread over four or five thermal tiles as the shuttle crew looked over the hull with a camera attached to an external boom.

"It doesn't look very serious," Mission Control said. "Those tiles are pretty thick. The nicks look to be pretty small."

The scratches are on the underside of the hull, about where the right wing meets the fuselage.

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This repair mission is especially risky — a rescue shuttle is on standby for the first time ever — because of the debris-littered orbit of Hubble.

Unlike other space flights, the astronauts can't reach the international space station because it is in a different orbit than the telescope.

"Again, right now, everybody's feeling pretty good that it's not something particularly serious," Mission Control told the astronauts. "We just want to make sure we do the right thing and complete all the analysis."

The debris strike was detected in launch images as well as sensors embedded in the wings.

Damage to the shuttle during liftoff has been a worry for NASA since Columbia was doomed by a chunk of fuel-tank insulating foam that broke off during launch in 2003.

Columbia's left wing was punctured, along a vulnerable edge. The nicks on Atlantis are in a less sensitive location.

Flight director Tony Ceccacci told reporters "it's too early to tell" whether the astronauts will need to conduct a more detailed inspection of that area.

Any additional survey, to determine the depth of the nicks, would be done Friday right before the second of five spacewalks planned for Hubble.

Even before damage was discovered, NASA was preparing shuttle Endeavour to rush to the astronauts' rescue if needed. Nothing so far has been found that would require a rescue.

Atlantis will catch up with the 19-year-old Hubble on Wednesday.

The astronauts will capture the aging observatory and, the next day, begin the first of five grueling spacewalks to install new cameras and equipment and repair some broken science instruments.

Those two instruments were never meant to be handled by spacewalking astronauts; telescope managers consider this difficult and have cautioned everyone that it might not work.

Meanwhile, Atlantis' launch pad took more of a beating than usual during Monday's launch.

The heat-resistant material that covers the bricks beneath the pad was blasted off an approximate 25-square-foot area. Some nitrogen gas and pressurized air lines also were damaged.

The damage to the bricked flame trench — which deflect the flames at booster rocket ignition — was near a previously repaired spot but not an area severely battered last year.

Monday's damage was not as bad, said NASA spokesman Allard Beutel.

The Associated Press contributed to this report.