NASA engineers worked overnight on Friday to assess images of space shuttle Discovery's heat shield after two days of intensive inspections and growing optimism the problems leading to the fatal 2003 Columbia accident are over.

This still image from NASA video shows a view of the US space shuttle Discovery from the International Space Station as it moves in for docking with the station's docking ring (lower right). The International Space Station was an orbiting full house after the shuttle Discovery's seven astronauts joined the two ISS occupants on a pivotal mission for space exploration. [AFP]

The shuttle reached the International Space Station on Thursday to bring the resident crew up to its full, three-member staff for the first time since the accident and to deliver more than 5,000 pounds (2,268 kg) of new equipment and supplies.

"Overall, we have a really clean vehicle," deputy space shuttle program manager John Shannon said during a briefing on Thursday evening. "We're really happy."

Preliminary results of the in-flight inspections, which were conducted by the shuttle astronauts using a sensor-studded boom and by the station crew, which photographed Discovery's heat-resistant belly tiles before docking, showed no damage from debris impacts during the shuttle's ride to orbit on Tuesday.

On the last shuttle flight a year ago, the fuel tank used on Discovery shed large pieces of insulating foam, although none struck the spacecraft.

The flight before that ended with the breakup of shuttle Columbia and the deaths of seven astronauts on February 1, 2003. Columbia was hit by debris falling from the tank during launch and broke apart as it attempted to fly through the atmosphere for landing.

NASA has said any more serious problems with the shuttle likely would spell the end of the program and seriously affect plans for the half-built $100 billion space station. The remaining modules, structural trusses and solar power arrays can only be carried and installed by the shuttles and must be done before the fleet is retired in 2010.

While managers scrutinize pictures of Discovery for anything potentially hazardous, the shuttle and space station crews planned on Friday to unload an Italian-built moving van stuffed with gear for the outpost.

In addition to food, clothing and other supplies, the module holds a freezer for experiment samples, a European Space Agency incubator to grow plants in space and a new oxygen generator so the station's crew size can eventually be doubled to six.

Later in the day, the shuttle crew was scheduled to reattach the 50-foot (15-meter) sensor boom to the spaceship's robot arm and take pictures and laser images of two strips of cloth poking out from surrounding tiles on Discovery's belly.

Shannon said the crew would also likely check an area beneath the shuttle's nose that may have a piece of loose fabric.

"We're struggling a bit to find areas to go look at," Shannon said. "It's somewhat of a surprise, but a pleasant surprise."