CAPE CANAVERAL, Fla.—With a sunny sky as the perfect backdrop, astronauts climbed aboard space shuttle Discovery on Saturday for a late afternoon launch to the international space station.

Everything seemed to be going NASA’s way, including the weather.

Commander Mark Kelly and his six crewmates waved and smiled broadly as they headed out to their fueled spaceship at the launch pad. “Good to be aboard,” he told launch controllers.

Loaded aboard Discovery was Japan’s precious lab, a $1 billion addition for the space station that will be the biggest room by far. It’s named Kibo, Japanese for hope.

Also tucked away in the space shuttle: a new pump for the space station’s finicky toilet. For more than a week, the three occupants have had to manually flush the toilet with extra water several times a day, a time-consuming job.

NASA and Russian space officials are hoping that the pump—which was rushed to Kennedy Space Center from Moscow just three days ago—gets the toilet back in normal working order.

Nearly 400 Japanese journalists, space program officials and other guests jammed NASA’s launch site, their excitement growing with every passing minute of the countdown.

Their enthusiasm was catchy.

“This is a real milestone,” NASA Administrator Michael Griffin said.

The Japanese lab is 37 feet long and more than 32,000 pounds, and fills Discovery’s entire payload bay. The first part of the lab flew up in March, and the third and final section will be launched next year.

The entire lab, with all its pieces, cost more than $2 billion.

A large political contingent was also on hand led by Rep. Gabrielle Giffords, D-Ariz., who’s newly married to Kelly, Discovery’s commander. They invited numerous bigwigs from Arizona and Washington.

Giffords acknowledged being nervous, far more so than the day she was elected to Congress in 2006.

“It’s a risky job. I’m pleased that the vehicle’s in good shape, the weather is beautiful. They’ve had no problems,” she told The Associated Press. “But you don’t really relax” until the shuttle is back from its two-week mission.

Kelly’s brother, Scott, didn’t need an invitation to the launch—he’s also a space shuttle commander. They’re identical twins.

Scott Kelly said it was more nerve-racking to watch his brother launch than to be strapped in himself. Their parents and 91-year-old grandmother are always anxious on launch day, he said.

“I know my grandmother, she would rather I work at Wal-Mart,” Scott Kelly said, chuckling, as the countdown entered the final hours.

Three spacewalks are planned during Discovery’s 14-day flight, to install Kibo, replace an empty nitrogen-gas tank and try out various cleaning methods on a clogged solar-wing rotating joint.

One of Discovery’s astronauts, Gregory Chamitoff, will move into the space station for a six-month stay. He’ll replace Garrett Reisman, who will return to Earth aboard the shuttle.