Houston ? The shuttle Discovery backed away from the international space station and started a two-day journey home after its crew bade farewell to the residents of the orbiting outpost and left behind U.S. astronaut Suni Williams for a six-month stay.

Discovery is scheduled to return to Earth on Friday after a 13-day flight.

Under the control of pilot William Oefelein, the shuttle pulled about 450 feet back from the space lab before its jets were fired. Discovery will stay about 46 miles from the station for an inspection of its heat shield today, allowing the astronauts to return to the space lab in case damage is found.

During eight days at the space station, Discovery’s astronauts made four spacewalks, during which they rewired the station’s power system, installed a 2-ton addition and coaxed a stubborn solar panel to fold up accordion-style into its box.

The fourth spacewalk extended the mission by one day and put astronaut Robert Curbeam, above, in the history books, with a record four spacewalks in a single shuttle mission.