After delivering the final US components to the International Space Station (ISS), NASA’s space shuttle Discovery has started its final trip back to Earth.

Discovery, which flew more than any other space shuttle in the fleet in its 27-year career, is scheduled to land at the Kennedy Space Center, Florida, at 11:57 a. m. EST on Wednesday. The backup landing opportunity for the spacecraft is available at 1:34 p. m.

Discovery and its six-member crew have delivered a storage room, a humanoid robot and other essentials to the ISS, which has been under construction since 1998, at an altitude of 220 miles from Earth.

NASA is going to retire its entire felt of space shuttles. Discovery’s current mission is its 39th and final mission.

Speaking on Discovery’s final mission, Johnson Space Center director Michael Coats said, "You're sad to see an orbiter on its last mission that's about to go into a museum. But it also makes you feel proud of the team and what they've accomplished in the last 30 years.”

NASA will send two more space shuttles to the ISS before putting an end to its 30-year-old shuttle program. Space shuttle Endeavour is scheduled to blast off on 19th of April, while shuttle Atlantis is slated to launch on 28th of June.

Following the retirement of NASA’s own space shuttle fleet, the US will depend on Russian space shuttle to deliver astronauts and equipment to the ISS.