This story was updated at 12:46 p.m. EDT.
HOUSTON - The International Space Station (ISS) is back at full strength once more after NASA's Discovery shuttle astronauts delivered a third crewmember to the orbital laboratory Thursday.
Discovery's STS-121 seven-astronaut crew, with shuttle veteran Steven Lindsey in command, docked at the ISS right on time at 10:52 a.m. EDT (1452 GMT) as the two spacecraft passed over the Southern Pacific Ocean. Riding aboard the orbiter was German astronaut Thomas Reiter, who will return the ISS back to its three-person capacity for the first time since the 2003 Columbia accident.
"It's great to see you out the window," ISS Expedition 13 flight engineer Jeffrey Williams told the oncoming Discovery astronauts.
Williams has lived aboard the ISS since April 1 with Expedition 13 commander Pavel Vinogradov. The two astronauts are in the middle of a six-month mission aboard the space station.
"Good to see you Jeff, we're proceeding along normally here, you guys look great," Discovery's STS-121 commander Steven Lindsey called to the ISS.
Hatch opening between the two spacecraft occurred 12:30 p.m. EDT (1630 GMT), with a jubilant and warm welcome of hugs and smiles awaiting the STS-121 shuttle crew.
Lindsey flew Discovery through an orbital back flip while stationed about 600 feet (182 meters) below the ISS just before docking. The maneuver allowed the Expedition 13 crew to take a series of high-resolution photographs of the orbiter's tile-covered belly heat shield.
Analysts will sift through the images to seek out any signs of tile damage that could prevent the orbiter from returning to Earth. So far, shuttle officials have said the orbiter's heat shield is in fine shape, but that today's back flip photographs will allow for a more informed decision.
In particular, mission managers hope to learn how a series of about 5,000 gapfillers - which are wedged between some shuttle tiles - performed during Discovery's launch. The gapfillers were replaced after the orbiter's last flight using a new process to fix them in place.
An older gapfiller, installed in 1982, is sticking out from under Discovery's port wing just behind its leading edge, but is likely not a concern, said John Shannon, NASA's deputy shuttle program manager, Wednesday.
Today's orbital arrival caps a two-day spaceflight for the STS-121 crew that began with a July 4th launch from NASA's Kennedy Space Center in Cape Canaveral, Florida. In addition to Lindsey and Reiter, Discovery launched toward the ISS with shuttle pilot Mark Kelly and mission specialists Michael Fossum, Lisa Nowak, Stephanie Wilson, and Piers Sellers.
According to a NASA cargo manifest, Discovery is hauling more than 3.6 tons of supplies, equipment, food and spare parts to the ISS, some of which is tucked inside the orbiter's Italian-built Leonardo module, while more is stowed in the spacecraft's middeck and payload bay platforms.
NASA's STS-121 mission is the second orbiter test flight since the Columbia tragedy that destroyed one space shuttle and claimed the lives of seven astronauts. The space agency's first post-Columbia flight - STS-114, also aboard Discovery - launched to the ISS in July 2005.
While the STS-121 mission will perform many of the test objectives left unfinished from that first spaceflight, it will more importantly return the ISS back to its three-person capacity.
"Fundamentally, we're building the space station as a permanent toehold off of Earth for our expansion into space," NASA chief Michael Griffin said before Discovery's launch. "Putting three people back aboard is a big step forward in the health of the program."
Back to full strength
An experienced long-duration astronaut from his days on the Russian Mir orbital complex, Reiter is Germany's first spaceflyer to the station and the first European Space Agency (ESA) participant in an ISS expedition. His position on Expedition 13 is part of an arrangement between Russia's Federal Space Agency and ESA officials.
But Reiter's ISS arrival did not automatically make him part of the station crew.
First, he must bring in the seat liner for his slot aboard the Russian-built Soyuz spacecraft that ferried the Expedition 13 crew to the ISS in April. The seat also serves as an escape craft in the event of an emergency. Reiter is scheduled to move his Soyuz seat liner into position later today.
Busy week ahead
With the arrival of Discovery at the ISS, a busy week - or about eight days - begins for the two spacecraft crews.
Later today, shuttle astronauts will use Discovery's 50-foot (15-meter) to hand off the orbiter's sensor-laden inspection boom to the space station's robotic appendage. The boom hand-off will clear Discovery's arm to install the Leonardo cargo module at the ISS on Friday, beginning the long process of transferring supplies between the two spacecraft.
The STS-121 mission's first spacewalk will begin on July 8, with at least one more planned for July 10. A third spacewalk could be added to the mission later depending on Discovery's available fuel cell propellant.
But despite that busy schedule, the Expedition 13 astronauts do hope to be good hosts and spend some quality time with their shuttle counterparts.
"I think we'll get an opportunity, like we do when we're on the ground when we're enjoying times with our friends," Williams said before Discovery launched. "In this case, it means floating around the dinner table and sharing our experiences. I think those will be the most special times that we have with the shuttle crew here."
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