"We wish them the best with their expedition and we hope we left them a better, more capable space station than when we arrived. Sayonara," shuttle commander Mark Kelly told the space station crew before leaving.
After the shuttle undocked, pilot Ken Ham backed Discovery away and guided it around the space station so the crew could take pictures. After that, the shuttle fired its engines and started its trip back to Earth.
Gregory Chamitoff, the station's newest crew member, rung the station's bell as the shuttle left, a tradition borrowed from the Navy. He traded places with astronaut Garrett Reisman, who lived aboard the orbiting outpost for three months. Chamitoff will stay on the station for six months.
Later, Discovery's astronauts pulled out a laser-tipped inspection boom and began surveying the ship's wings and nose cap for any damage. The inspection was to last several hours.
The laser survey normally is conducted the day after liftoff, but Discovery didn't have room for the inspection boom because of the giant science lab, called Kibo, that filled its payload bay. So they retrieved the boom from the space station after it was left by another shuttle in March.
The inspection, which will look for any damage from debris generated during the May 31 launch or from micrometeorites in orbit, is one of the safety measures put in place by NASA after the 2003 Columbia accident. Columbia was destroyed during re-entry as a result of a gashed wing.
Flight director Matt Abbott said photography and data collected so far on the shuttle's thermal protective shield indicate the ship is in good shape.
"We haven't seen anything that gives us any indication of concern at this point," Abbott said Tuesday.
Besides delivering and installing the new lab, Discovery also brought a pump that fixed the space station's malfunctioning toilet. The problem had forced the station's three-man crew to flush manually with extra water several times a day.
The 37-foot lab, about the size of a bus, is the biggest room at the space station. Kibo also has a storage closet and a 33-foot robotic arm. A final section — a "porch" for exterior experiments — and a second, smaller robotic arm will be delivered next year. More technology news | Houston blogs | Houston headlines on Twitter | RSS feeds