Astronaut Scott Kelly's identical twin pulled a fast one on NASA right before his brother blasted off on a one-year space station mission.

NASA Administrator Charles Bolden told Kelly on Monday that he almost had a heart attack when his brother showed up launch morning without his usual mustache late last week.

"He fooled all of us," Bolden said. Mark Kelly's mustache was "the only way I can tell you two apart."

Mark, a former space shuttle commander, was still clean shaven as of Monday afternoon, as he chatted with Bolden about the unprecedented medical experiments planned on the twins over the coming year. Doctors want to see how the space twin's body compares with his genetic double on the ground.

Scott Kelly arrived at the International Space Station on Friday night following a launch from Kazakhstan. He will remain on board until next March, as will Russian cosmonaut Mikhail Kornienko.

It will be NASA's longest spaceflight ever.

"It's like coming to my old home," said Kelly, who spent five months at the space station in 2010-2011.

The White House, meanwhile, sent congratulations Monday.

President Barack Obama's science adviser, John Holdren, wished Kelly, Kornienko and the rest of the crew the best of luck and noted that the yearlong mission is an important milestone on the path to sending humans to Mars in the mid-2030s.

"You guys are all heroes up there, and we're depending on you," Holdren said in a phone hookup.

Mark Kelly, meanwhile, paid tribute to the brothers' father, who stayed behind in Houston for last week's launch. Richard Kelly, a retired and widowed police officer, is the only parent to endure a child's rocket launch so many times — eight between the two.

"He's been a trouper," Mark said.