HOUSTON – 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 airlock 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 Ms. Collins with a handshake.

The linkup marked the first time a shuttle has visited the space station since Endeavour docked on November 25, 2002. Just over two months later, the shuttle Columbia disintegrated on re-entry, grounding the shuttle fleet for two and a half years until Discovery’s liftoff Tuesday from Kennedy Space Center at Cape Canaveral, Fla.

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.

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 following the Columbia disaster, Discovery performed a “rendezvous pitch maneuver” during its final approach to the space station to expose the orbiter’s underside so Mr. Krikalev and Mr. Phillips could look for any damage to the heat shielding and photograph sensitive areas.

This unprecedented, 360-degree backflip began over Europe at 6:15 a.m. Eastern time yesterday when Ms. 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, Ms. Collins began her lazy loop, all of it captured in full color by television cameras on the station.

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