CAPE CANAVERAL, Fla. — Space Shuttle Discovery landed safely in Florida on the morning of April 20 to wrap up a 15-day delivery mission to the international space station and one of NASA’s few remaining shuttle flights before the orbiter fleet is set to retire later this year.

Shuttle commander Alan Poindexter guided Discovery to a 9:08 a.m. touchdown at the Shuttle Landing Facility at NASA’s Kennedy Space Center here following a flight path that took the shuttle over much of North America before avoiding rain showers falling over most of central Florida.

Returning to Earth inside Discovery’s payload bay was the Leonardo Multi-Purpose Logistics Module (MPLM), a cargo vessel that carried nearly 8 tons of supplies for the station, including a new crew sleeping quarters, ammonia coolant tank and four experiment racks. Leonardo returned packed with almost 3 tons of science results and trash.

This was the final round trip for Leonardo to the station after six previous flights. Its next mission, aboard Discovery in a flight scheduled for September, is the last planned for the shuttle program. During that mission, Leonardo will be installed at the station as a closet and storage space for the crew.

Discovery landed a day late due to rain. Its re-entry over North America offered a special treat to skywatchers who may have had a chance to spot the bright meteor-like streak of its plasma trail as it flew from the northwest coast of Canada to the southeastern United States for landing. The last time a shuttle made such an approach was in 2007.

NASA typically tries to have space shuttles re-enter from the southwest — an approach that is mostly over the southern Pacific Ocean, parts of Central America and the Gulf of Mexico — to avoid flying over populated areas.

Discovery’s STS-131 mission left the space station 98 percent complete but was not without its share of minor snags.

Just after Discovery’s launch, the astronauts and flight controllers discovered that the shuttle’s Ku-band communications antenna had failed. The antenna is used to provide radar data during the shuttle’s approach to and separation from the station as well as to transmit high bandwidth data — such as live video — during the mission.

Although the crew was trained to compensate for the loss of the system, it resulted in a mission extension to allow time for the standard final inspection of the orbiter’s heat shield before Discovery undocked from the |station.

The mission almost gained another extra day as mission managers debated having the shuttle astronauts make an unplanned spacewalk after they had already completed the mission’s three planned outings to replace an 810-kilogram ammonia coolant tank.

Though their work was hampered several times by sticky bolts preventing the removal and installation of the tank assemblies, it was a stuck valve on a nitrogen tank that fed into the replacement ammonia assembly that gave flight controllers reason for concern.

Flight controllers ultimately decided that the problem did not pose a hazard and ruled out the extra spacewalk, opting instead to continue troubleshooting from the ground.

“We expect to always hit some unexpected difficulties, like we did on our flight with the ammonia tank bolts, but the crew is really well-trained and we have outstanding engineering and operational support on the ground,” Poindexter said from orbit April 18.

By contrast, the work inside the station to move and install equipment delivered by the shuttle proceeded smoothly. The crew installed a refrigerator-size rack designed to augment the U.S. Destiny laboratory’s science-quality window with multiple man-tended and remotely controlled camera mounts, as well as a novel device designed to create water for the station’s crew using waste hydrogen and carbon dioxide gases.

STS-131 was the 33rd shuttle mission to the space station and marked Discovery’s 38th and next-to-last flight.