The space shuttle Discovery touched down in Florida to successfully end a 15-day mission that is seen as among the most challenging in shuttle history.

"Discovery's rolling out on runway 33, capping off a 6.25-million-mile mission," a NASA announcer said Wednesday.

The flight was Discovery's 34th mission and the 23rd shuttle flight to the International Space Station, the announcer said.

"It's good to be back in Florida," responded one unidentified astronaut.

Discovery passed over British Columbia, Montana, Wyoming, the Great Plains, the Deep South and finally into Florida before touching down at the Kennedy Space Center.

The route allowed the astronauts more rest and helped them avoid a riskier night landing.

The last such coast-to-coast re-entry ended in tragedy on Feb. 1, 2003, when the Columbia shuttle burned up during re-entry, killing all seven astronauts aboard.

Discovery and its seven astronauts blasted off on Oct. 23 to the station, hooking up with the three astronauts there in a mission that was considered to be the most complicated so far in the nine years of orbital assembly of the ISS.

The crew delivered and installed a seven-metre-long pressurized compartment to the station. The new module will serve to effectively double the size of laboratory space on the station.

The Italian-built, multi-port module named Harmony will function as the docking port for European and Japanese laboratories that are scheduled for launch in December.
 
The crew also had to move a massive solar power tower -- about half the length of a football field -- to the far left end of the ISS.

They also had to conduct the unscheduled repair of a solar panel tear, which threatened to hamper power production and future construction work on the orbital outpost if not fixed.

Without repairs, the wing's tear could have worsened and caused structural damage to the ISS. If the wing became unstable, NASA would be forced to cut it loose and risk losing a vital power source for future laboratories.

Experts are calling the repair job one of the most difficult and dangerous ever attempted in orbit. U.S. astronaut Scott Parazynski accomplished it in a single spacewalk.

The historic repair effort will now allow NASA to continue with plans to launch the shuttle Atlantis in December.

With files from The Associated Press