Space shuttle Discovery slipped into a parking spot at the International Space Station on Monday after a two-day voyage to deliver Japan's first orbital laboratory while managers on the ground assessed damage beneath the Discovery's launch pad.

NASA officials revealed on Monday that bricks and mortar came off a trench beneath the seaside launch pad at Cape Canaveral in Florida as Discovery blasted off on Saturday, but they said it could be repaired before the pad is needed next.

The concrete-fortified trench helps to deflect the intense heat of shuttle launches.

Apart from that problem, the mission - which is devoted to the installation of Japan's orbital laboratory - was smooth sailing. "It's one big happy spaceship now ... Just a flawless day," said lead shuttle flight director Matt Abbott.

Commander Mark Kelly lined up Discovery's docking port with a matching clasp on the space station's Harmony module, which serves as the vestibule for visiting space shuttles. The docking rings locked together at 2:03 p.m. EDT (7:03 p.m. British time), 210 miles (338 km) above the south Pacific.

"Discovery, arriving," announced station flight engineer Garrett Reisman, ringing a ship's bell in a tradition adopted from the U.S. Navy.

TOILET REPAIR

In addition to delivering Japan's $1 billion (509.4 million pounds) Kibo laboratory, a 37-foot-long (11-metre-long) module that will become the station's largest piece of real estate, Discovery ferried a new station crew member and critical equipment to repair the outpost's sole toilet.

Greg Chamitoff, a Canadian-born astronaut on his first spaceflight, will transfer to the station crew, replacing Reisman who will return with the shuttle.

Before berthing Discovery, Kelly coaxed his ship through a slow back-flip so Reisman and space station commander Sergei Volkov could snap pictures of Discovery's belly tiles. Engineers will study the images to make sure the shuttle reached orbit with its heat shield unscathed.

Damage inspections have been a routine part of shuttle missions since the 2003 Columbia disaster which was caused by damage to the shuttle's heat shield during launch.

More inspections are planned for later in the current mission. Because Kibo is so big, the shuttle had to fly without its laser-studded inspection boom, which is usually used to scour the ship's wings and nose cap for damage.

Instead, the Discovery astronauts used a camera on the end of the shuttle's 50-foot (15-metre) robot arm, but they couldn't reach the underside of the wings. An inspection boom was stashed outside the space station by the last shuttle crew for the Discovery astronauts to use and then return to Earth.

Retrieving the boom will be among the first jobs for spacewalking astronauts Michael Fossum and Ronald Garan, who are scheduled to make three outings starting on Tuesday to attach Kibo and tackle a variety of maintenance chores.

At Cape Canaveral, NASA managers said debris from the flame trench was strewn around the launch area. They described the incident as "unprecedented," but they said they were confident it could be repaired in time for October's shuttle mission to the Hubble Telescope.

"We'll fix it without any problems before October," deputy shuttle program manager LeRoy Cain told reporters at the Johnson Space Center in Houston.

NASA needs two launch pads at the ready for the Hubble mission as there is no escape craft at the telescope which could be used in the event that the visiting shuttle could not return. A second launch pad, for a backup shuttle, has to be ready.