Obama checks up on astronauts — and their robot

The 12 orbiting astronauts on the International Space Station were hailed by the chief on Thursday — and also got a humorous scolding for keeping their android crewmate locked up in its packing for so long.

Over an Earth-to-space audio link, President Barack Obama praised the combined crews of the shuttle Discovery and the space station for their work during Discovery's final spaceflight, which he called a "critical and iconic mission."

"You are setting such a great example with your dedication, your courage, your commitment to exploration," Obama told the astronauts. "These are traits that built America, and you guys personify them."

On its final space trip before retirement, Discovery brought up a walk-in storage closet called Leonardo that was stuffed with supplies and equipment, including a humanoid robot named Robonaut 2 or R2.

Obama referred to R2 during his phone call: "Are you guys making him do chores up there? Washing the dishes or something?"

Discovery commander Steven Lindsey told the president that the robot wasn't on the job quite yet. "He's still in packing foam, so we hope to get him out shortly," Lindsey said.

"That's a shame, man," Obama joked. "C'mon, guys, unpack the guy."

Lindsey played along with the joke, saying that "every once in a while we hear some scratching sounds from inside."

R2 is due to stay in its packing case until well after Discovery's departure. Eventually, the two-armed torso will be tested on simple tasks inside the space station.

Obama also had some words of encouragement for NASA astronaut Scott Kelly, the space station's current commander. Scott Kelly's twin brother, Mark, is also an astronaut who is scheduled to head the next shuttle mission. Mark Kelly's wife is U.S. Rep. Gabrielle Giffords, who is recovering from wounds suffered during a gunman's attack in January.

The president said he heard from Mark Kelly that Giffords was making "incredible progress," and he told Scott that she was "always in our thoughts and prayers."

"Yes, sir, thank you. She's really a true inspiration to all of us," the station commander said.

Mission extended to 13 days
With the major objectives of their joint mission behind them, the station and shuttle crews had most of the day off — and found out that they're getting an extra day to savor their time in outer space.

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On Thursday, NASA managers added a 13th day to Discovery's mission, which already had been stretched earlier in the week to 12. When notified about "the extra extra day," Lindsey called it great news. "We're excited," he said.

Lindsey referred to the extension during his chat with the president, noting that by his reckoning, Discovery will have spent 365 days in space over more than 26 years of service. "She won't be forgotten for a long, long time, we hope," Lindsey said.

Other crew members reviewed Discovery's mission and its history in a series of TV interviews earlier in the day.

Discovery astronaut Alvin Drew said that when he floated out on his first spacewalk this week, "I had to keep reminding myself that I had a job to do and not just take in this gorgeous scenery around me."

"You are part of the scene. You've gone through the looking glass," he said.

Reflections on final voyage
Astronaut Nicole Stott said she and her crewmates have talked a lot about Discovery's final voyage. NASA's oldest shuttle will be retired once it returns to Earth next week and be sent to a museum.

Endeavour will make its farewell flight in April, and Atlantis will close out NASA's 30-year shuttle program this summer.

Stott noted that the word "bittersweet" is used quite a bit to describe this last flight of Discovery, which she called "a really, really high-performing spacecraft."

"I tend to think more 'bittersad,'" she told an interviewer.

She added: "It's just a part of history that I hope we hold on to and appreciate and that we celebrate when we get home and are walking away from her on the runway for the last time."

Discovery will remain at the space station until Monday, two days longer than originally planned. The extra time will be used to unload supplies and experiments from the Leonardo storage unit.

Landing is now scheduled for Wednesday.

More about Discovery's mission:

• Space shots galore for shuttle fans
• Robot butler catches a ride on Discovery
• Where will the shuttles go? We'll know April 12

This report includes information from The Associated Press and msnbc.com.