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 / Updated  / Source: TODAY
By Scott Stump

Identical twin astronauts Scott and Mark Kelly reunited Wednesday on TODAY and proved that brotherly ribbing doesn't stop when one of them is in space.

Scott and Mark, 50, are participating in a unique NASA study of the impact of long-term space missions on the human body. But on Wednesday, they were just like any two brothers on Earth as Mark spoke with Scott about the fact that he will be three extra milliseconds older than Scott, who is a month into a planned year mission aboard the International Space Station, once he returns from space.

"Well, I'm already six months older, so I'm going to gain another three milliseconds,'' Mark told Savannah Guthrie. "Einstein figured that out, the general theory of relativity, so yeah, we'll see what happens with those three milliseconds."

"First, I need to correct my brother,'' Scott responded from the ISS. "He said he was six months older. He's really only six minutes older. I know sometimes he thinks he's more like six months, and he's really only six minutes."

After requesting that Scott spin upside down to show that he was in space, Mark kept up the brotherly badgering, saying that Scott should change a U.S. Air Force sign in the background to one of the U.S. Navy, where Mark was a captain before becoming an astronaut.

More from Scott Kelly:

  • On the space station's new espresso machine: "There are little things that make life here more normal like the espresso machine, which we just got running,'' Scott said. "Which, by the way, is a science experiment. We only have 15 espresso capsules so we're kind of rationing those, but it worked great, tasted great."
  • Kelly has been regularly tweeting beautiful images of Earth from the space station. Check out some of his best on Instagram.

Follow writer Scott Stump on Twitter and Google+.