Crew members aboard space shuttle Discovery on Thursday combed the outside of the vehicle with a laser-tipped tool in a final inspection before they head back to Earth.

Astronauts conducted the routine procedure using Discovery's robotic arm attached to a 50-foot inspection boom.

"That's a perfect view," Mission control radioed the astronauts as the boom passed over Discovery's right wing.

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They were looking for damage from micrometeorites that may have hit the shuttle as it was docked to the international space station for eight days. The results will be compared with those taken during an inspection on the mission's second day.

The procedure was put in place after the 2003 Columbia disaster killed seven astronauts. A piece of foam from Columbia's external tank damaged the shuttle's wing during launch, allowing fiery gases to penetrate the orbiter during its descent back to Earth.

Discovery and its seven-person crew are due back on Earth on Saturday after its mission to deliver and install power-generating solar wings at the space station. Discovery undocked from the space shuttle on Wednesday.

Among the crew heading back was astronaut Sandra Magnus, who had lived four months at the space station. She spent two sessions on the shuttle's exercise machine Thursday in order to prepare her body for the effects of gravity.

"Sandy is on her way home," space station commander Mike Fincke radioed Mission Control. "We certainly enjoyed working with her."

As Discovery left the space station's neighborhood 220 miles above earth, another space vehicle was headed its way.

A Soyuz capsule carrying Russian cosmonaut Gennady Padalka, U.S. astronaut Michael Barratt and U.S billionaire space tourist Charles Simonyi blasted off for the space station Thursday from the Baikonur cosmodrome facility in Kazakhstan.

Padalka and Barratt are replacing Fincke and Russian flight engineer Yury Lonchakov as long-term residents at the orbiting outpost.

Simonyi's second trip to the station as a space tourist will last until April 7, when he'll return to Earth with Fincke and Lonchakov aboard the Soyuz.

Fincke watched the launch live on television from the space station and called it "picture-perfect."