After receiving a wake-up message from Star Trek's William Shatner on Monday morning, the crew of NASA's space shuttle Discovery undocked from the International Space Station and began its final voyage back to Earth.

Discovery, which will be retired after returning from its 39th mission, fired its jets to separate from the space station for the final time, setting it on a course for its return to the Kennedy Space Center in Florida. Flying into space for more than 26 years, the shuttle's last mission included delivering supplies, spare parts, experiments and a humanoid robot to the international orbiter.

The day got off to an engaging start when Shatner, who played Captain James T. Kirk on the original Star Trek television series and several movies, recorded a message on the wake-up call to the members of the Discovery crew on their eighth day docked to the space station.

As the familiar theme music from Star Trek played, Shatner replaced the usual introduction for the TV series with a voice-over, saying, "Space, the final frontier. These have been the voyages of the Space Shuttle Discovery. 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."

Discovery first launched into space in August 1984. It was the shuttle that returned the US to space flight after the shuttle Challenger and Columbia accidents. It also was the shuttle that carried the Hubble Space Telescope into orbit and has since gone aloft twice so astronauts could make repairs to the telescope.

During its last mission, astronauts made two spacewalks and removed the Leonardo Permanent Multipurpose Module from the space shuttle and permanently attached it to the outside of the space station. The module is a pressurised container used on shuttle missions to haul cargo to the space station and refuse back to Earth.

However, with the shuttle fleet close to retiring, this time the module became a permanent fixture on the space station, giving astronauts living there more storage room.

And as the module was attached to the space station, the humanoid robot, named Robonaut 2, officially reached its permanent home aboard the space station. The robot had travelled into space inside the module.