The U.S. space shuttle Atlantis was hit by a piece of debris that nicked part of its heat shield that caused a 21-inch stretch of nicks, although Nasa said that the damage did not appear to be serious.

The scratches were found on the forward part of the shuttle's right wing close to where it connects to the fuselage, according to NASA spokeswoman Katherine Trinidad.

Atlantis and its seven-member crew blasted off from Florida on Monday on an 11-day mission to repair the Hubble Space Telescope.

NASA said the image looks minor but it will continue to investigate it, while also looking for any other damage on the space shuttle which is orbiting about 350 miles above the Earth.

Everybody is feeling pretty good that it's not something potentially serious, mission control astronaut Dan Burbank radioed to Atlantis commander Scott Altman.

The damage seems to be related to a debris impact that occurred about 104 seconds after the Atlantis lifted off the ground yesterday afternoon. The liftoff damaged about 25 square feet of the shuttle's launch pad flame trench, the U.S. space agency said.