US astronauts awoke to actor William Shatner\'s voice and theme music to the movie Star Trek on their final day at the International Space Station before starting their journey back to Earth.

The space shuttle Discovery(C) departs the International Space Station (ISS) seen in this NASA TV image.

"Space, the final frontier. These have been the voyages of the Space Shuttle Discovery," said Shatner in a specially recorded introduction to the "Theme from Star Trek," played as wake-up music at 2:23 am (0723 GMT).

"Her 30 year mission: To seek out new science. To build new outposts. To bring nations together on the final frontier. To boldly go, and do, what no spacecraft has done before," said Shatner, who played Captain Kirk in the popular television and movie series.

The music was chosen by public vote in a NASA contest to pick theme music for the astronauts\' wake-up call.

Discovery, NASA\'s oldest and most traveled shuttle and the first of the three-member fleet set for retirement when the US program ends later this year, separated from the ISS after spending eight days and 16 hours there on its last mission.

"At 8:37 am EST (1337 GMT), space shuttle Discovery fired its jets to separate from the International Space Station for the final time," NASA said.

Discovery and its six-member crew of American astronauts are on course to land at Kennedy Space Center in Florida at 11:58 am (1658 GMT) Wednesday after a 13-day trip.

NASA said an inspection of Discovery\'s heat shield will begin at 11:13 am (1613 GMT), and a press conference was set for 1:30 pm (1830 GMT).

Discovery\'s six US astronauts helped the six crew members already on board the International Space Station install a new permanent module that offers extra space for storage and experiments, and delivered the first humanoid robot.

The space shuttle Endeavour is to lift off on April 19 followed by Atlantis on June 28, marking the official end of the US space shuttle program after 30 years.