The space shuttle Discovery undocked from the International Space Station for the last time Monday morning and started its two-day journey back to the Kennedy Space Center.

The space shuttle Discovery undocked from the International Space Station for the last time Monday morning and started its two-day journey back to the Kennedy Space Center.

The shuttle fired its jets to separate from the ISS at 8:37am Eastern, NASA said. Discovery is scheduled to land at 11:58am on Wednesday; at this point, weather conditions are favorable.

Overall, the astronauts engaged in seven days, 23 hours, and 55 minutes worth of joint activities with the ISS crew. This is Discovery's 39th and final mission.

The crew received a special wake-up call at 3:23am this morning: the theme from "Star Trek" and a recorded message from actor William Shatner. "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," Shatner said.

NASA said the message was particularly poignant because Discovery was the first space shuttle to dock at the ISS in 1999, "marking just one time it did what no spacecraft had done before."

The undocking began at 7am while Discovery was 220 miles above the western Pacific, northeast of New Guinea. The shuttle then flew around the space station, allowing the crew to photograph it with the new Leonardo Permanent Multipurpose Module. It then fired its engines to start increasing the distance between the two vehicles.

This afternoon, the crew will conduct a final inspection of Discovery's heat shield using the orbiter boom sensor system and its suite of cameras. The imagery collected during the survey, which starts at 11:13am, will be sent to analysts back on Earth, who will study it to make sure Discovery's thermal protection system has not been damaged while in space.

In a farewell ceremony, Discovery Commander Steve Lindsey thanked the remaining station crew members. "We had a great time onboard with you," replied station Commander Scott Kelly. "We'll miss you, but most of all we'll miss Discovery. We wish her fair winds and following seas."

During their stay Discovery crew members delivered and helped install the Leonardo module, which included 6,500 pounds of cargo for the station, an Express Logistics Rack 4 for the station's exterior, and an additional 2,000 pounds of cargo on the middeck. Crew members also , during which they conducted a number of maintenance and installation tasks. They also (below).