NASA engineers, meanwhile, tried to determine whether an apparently chipped thermal tile on the belly of the shuttle poses any danger to the spacecraft and its crew of seven.
Discovery lifted off on Tuesday on the first shuttle flight since the Columbia tragedy two-and-a-half years ago. The movable boom operated by the astronauts via remote control from inside was added to the shuttle after Columbia was destroyed by damage to its thermal shield at liftoff.
The inspection was planned all along, before NASA discovered that an object believed to be a one-and-a-half-inch piece of thermal tile appeared to break off from a vulnerable spot near the nose landing-gear doors on the underside of Discovery during liftoff.
Also, a large object perhaps a piece of foam insulation seemed to fly off from the big external fuel tank but did not hit the shuttle.
Officials stressed it was too early to say whether there was any danger to the shuttle or its crew.
NASA planned to stick to its original work schedule and inspect only the nose and wings yesterday, examining the dozens of reinforced carbon panels that withstand the heat during re-entry into Earth's atmosphere.
Also today, Discovery will execute a slow backflip as it approaches its destination in orbit the International Space Station so that the station's crew members can photograph the shuttle from various angles.
That manoeuvre, too, was planned well before any damage was detected.
Neither the astronauts nor mission control had any immediate comment on the results of the inspection.
The shuttle chased after the station yesterday, drawing closer with every orbit of the Earth.
When the astronauts awoke, the shuttle trailed the station by 5,500 miles.
The highly sensitive inspection, which took around seven hours, employed a brand-new 50-foot extension of the shuttle's 50-foot robotic arm.
The astronauts had to be careful not to bang the equipment against the shuttle's fragile thermal shield.
Flight director Paul Hill has said the inspections are some of the most hazardous of the new procedures put in place since the Columbia tragedy.
"If we make contact with the orbiter while we're doing this, I'm looking for another job," Hill said in the months leading up to the 12-day mission.
Meanwhile, astronauts Stephen Robinson and Soichi Noguchi tested tools and equipment they will use during three spacewalks.
During the spacewalks, the pair will try out new repair techniques for the shuttle's tiles and delicate carbon panels; replace a gyroscope, which helps steer the space station; and install a storage platform on the station.