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In his tweet, Kanai said the crew had their bodies measured after reaching space and initial measurements put him at over 3.5 inches taller than on Earth, making the astronaut fearful because the Soyuz spacecraft he needs to use to come home has a height limit of 6-foot-4.

\"PHOTO:
NASA
PHOTO: NASA and its international partners completed assembly of the International Space Station in the fall of 2011.
>

However, Kanai re-measured himself and, in a follow-up tweet, said he came in at a much more normal 0.79 inches. (Astronauts grow anywhere from .79 inches to 1.97 inches in space on average.)

In a later tweet, Kanai clarified the initial measurement was an error and apologized for sending out \"fake news\" after some news reports said he'd grown more than 3 inches.

Clayton Anderson, a former NASA astronaut, told ABC News that getting taller in space is normal. During his last trip in April 2010, he said he grew 2 inches.

“On Earth, gravity pulls on you, and so your spine is compressed,” Anderson said. “When you go into space, gravity is lessened and so your body begins to stretch.”

Seats in the space capsule are molded for a custom fit, so any growth in size can make for a tough squeeze.

Italian astronaut Paolo Nespoli, who grew two inches on his 138-day stay on the International Space Station in 2017, told ABC News it was a very uncomfortable ride home from the space station.

But taking measurements in space is far from scientific. As Anderson explained it, one must lie as stiff as a board and someone else holds the person by their feet so they don’t float away. Then a third person measures the first person's height. He said what likely happened is Kanai’s height was measured incorrectly the first time.

\"PHOTO:
John Raoux/AP Photo, FILE
PHOTO: Astronaut Clayton Anderson, a mission specialist on space shuttle Discovery, leaves the Operations and Checkout building on his way to board the shuttle on launch pad 39A at the Kennedy Space Center in Cape Canaveral, Fla., April 5, 2010
>

When asked if Kanai should be concerned about making it back to Earth, Anderson said he is not worried because once you return to Earth your spine shrinks back to normal.

“[Kanai] won’t be dunking in the NBA anytime soon,” he said, “but he’ll come back just fine.”

ABC News' Gina Sunseri contributed to this report.

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