The space shuttle Discovery docked smoothly with the international space station on Thursday, ending a two-day pursuit in space with a flawless linkup 222 miles above the South Pacific.

Mission commander Eileen Collins, wearing glasses as she watched instrument displays on the final approach, mated the 100-ton shuttle to the 200-ton space station precisely on schedule at 7:18 a.m. Eastern time with just a slight shudder.

After pressurizing the air lock connecting the two spacecraft and checking for leaks, space station commander Sergei Krikalev and flight engineer John Phillips opened the connecting hatch at 8:50 a.m. to welcome Collins with a handshake. Then a ship's bell rang over the station intercom:

"Discovery arriving," Phillips said.

The linkup marked the first time a shuttle has visited the space station since Endeavour docked on Nov. 25, 2002. Just over two months later, the shuttle Columbia disintegrated on reentry, grounding the shuttle fleet for 21/2 years until Discovery's liftoff Tuesday from Kennedy Space Center at Cape Canaveral.

NASA officials had expected Discovery's eight-day visit to be the opening sortie in an intense four-year schedule of shuttle missions designed to finish construction of the $5 billion space station by 2010, the first step in President Bush's initiative to send humans back to the moon and eventually to Mars.

But that timetable was thrown into disarray and the very future of the shuttle program was cast into doubt when NASA grounded the fleet Wednesday because large chunks of foam insulation had broken free of Discovery's external fuel tank during launch -- the same problem that fatally damaged Columbia.

With a lengthy stand-down possible and perhaps likely, Discovery's mission, rather than the first of many flights after the post-Columbia hiatus, could turn out to be the only flight in a considerably longer time.

As part of the new safety modifications after the Columbia disaster, Discovery performed a "rendezvous pitch maneuver" during its final approach to the space station to expose the orbiter's underside so Krikalev and Phillips could look for any damage to the heat shielding and photograph sensitive areas.

This unprecedented 360-degree back flip began over Europe at 6:15 a.m. Eastern time Thursday when Collins, driving by hand, brought Discovery to a position 600 feet directly below the station.

Then, with pilot James Kelly's status reports being relayed to the station by Mission Control at Johnson Space Center, Collins began her lazy loop, all of it captured in full color by television cameras on the station.

As the underside came into view, Kelly instructed Krikalev and Phillips to begin filming, then ordered "stop photos" 100 seconds later when the lighting conditions became unsuitable.

The orbiter's belly looked somewhat marked up, and perhaps scorched in spots, but it was impossible to evaluate the damage by watching the television image.

Collins took five minutes to finish the back flip, then moved ahead to begin the final approach, closing the station at a rate of a 10th of a foot per second.

"You're inside 250 feet," Mission Control said at 6:47 a.m.

"We'll knock when we get there," Kelly replied.