This story was updated at 9:15 a.m. ET.
CAPE CANAVERAL, Fla. ? Space shuttle Discovery landed safely in Florida on Tuesday morning to wrap up a 15-day delivery mission to the International Space Station (ISS), one of NASA's few remaining shuttle flights before the orbiter fleet retires later this year.
Shuttle commander Alan Poindexter guided Discovery to a 9:08 a.m. EDT (1308 GMT) touchdown at the Shuttle Landing Facility at NASA?s Kennedy Space Center, following a flight path that took the shuttle over much of North America before avoiding rain showers falling over most of central Florida. Twin sonic booms broke through the morning sky to announce the shuttle's homecoming after a 6 million-mile trip.
"Welcome home!" Mission Control radioed Poindexter and his crew. "Congratulations to you and your crew on an outstanding mission."
Riding home with Poindexter were STS-131 pilot James Dutton and mission specialists Dorothy "Dottie" Metcalf-Lindenburger, Stephanie Wilson, Rick Mastracchio, Clayton Anderson and Japanese astronaut Naoko Yamazaki. With just three flights remaining scheduled for NASA?s 30-year space shuttle program, the astronauts on Discovery's mission were the last seven-member crew to fly.
"It was a great mission," Poindexter told Mission Control. "The International Space Station is stocked up again."
Returning to Earth inside Discovery?s payload bay was the Leonardo Multi-Purpose Logistics Module (MPLM), a cargo module that launched on the shuttle on April 5 with nearly 8 tons of supplies for the station, including a new crew sleeping quarters, ammonia coolant tank and four experiment racks. Leonardo landed 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. It?s next mission, STS-133 targeted to launch on Discovery in September, the last planned for the shuttle program, will see its permanent installation on the ISS as a closet and storage space for the crew.
Discovery landed a day late due to rain, though its return to Earth was not affected at all by the vast ash cloud from Iceland's Eyjafjallaj?kull volcano.
The shuttle's re-entry over North America offered a special treat to skywatchers on Earth, who may have had a chance to spot the bright meteor-like streak of Discovery's plasma trail as it flew from the northwest coast of the Canada and United States to the southeast for its Florida 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 since the tragic loss of the shuttle Columbia, which broke apart over Texas during re-entry.
Malfunctions and sticky bolts
Discovery?s STS-131 mission left the space station 98 percent complete after 10 days docked together, but was not without its share of minor snags.
?I must say, I'm very proud of the teams on how well they handled and responded to all the adversities we've been faced with,? said lead space shuttle flight director Richard Jones.
Just after Discovery's launch, the astronauts and flight controllers discovered that the shuttle's Ku-Band communications antenna, used to provide radar data during the shuttle?s approach and separation from the station as well as transmit high bandwidth data ? such as live video ? during the mission, had failed.
Although the crew was trained to compensate for the loss of the system, it resulted in a mission extension to allow time for their standard final inspection of the orbiter?s heat shield to be conducted before Discovery undocked from the station.
The mission almost gained yet 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 a 1,800-pound 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.
At first considered a more pressing a problem that threatened to shut down half of the station?s systems, Mission Control ultimately decided 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,? said Poindexter from orbit on Sunday.
By contrast, the work inside the station to move and install equipment delivered by the shuttle proceeded smoothly. Led by the mission?s ?loadmaster? ? or cargo chief ? Yamazaki, 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.
Firsts and lasts
Discovery's STS-131 spaceflight was the 33rd shuttle mission to the International Space Station. It also marked Discovery?s 38th and next-to-last spaceflight.
The astronauts set several records during their time aboard the orbiting laboratory.
Together with station crew member Tracy Caldwell, STS-131 mission specialists Stephanie Wilson, Dorothy Metcalf-Lindenburger and Naoko Yamazaki represented the most women in space at the same time.
Similarly, Yamazaki and fellow Japan Aerospace Exploration Agency (JAXA) astronaut Soichi Noguchi, a station flight engineer, set the record for the most Japanese in space at one time.
Discovery also became the last orbiter expected to be in space over the anniversary of the first shuttle flight, STS-1.
With just three shuttle missions remaining, the next launch is scheduled for Atlantis in May.
By coincidence, Atlantis is due to roll out to its seaside launch pad at the Kennedy Space Center tonight. That launch pad trek ? the last planned one for Atlantis ? was also delayed a day because of bad weather.
- Images ? Shuttle Discovery's Mission in Pictures
- Morning Star: The Pre-dawn Launch of Shuttle Discovery
- Iceland Volcano's Ash Cloud No Threat to Space Shuttle Landing
SPACE.com is providing complete coverage of Discovery's STS-131 mission to the International Space Station with Managing Editor Tariq Malik and Staff Writer Clara Moskowitz based in New York. Click here for shuttle mission updates and a link to NASA TV.