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Associated Press
This undated file photo provided by NASA shows astronauts Mark Kelly, right, and Scott Kelly in the check-out facility at Ellington Field near NASA's Johnson Space Center in Houston. Scott and his twin Mark are taking part in an unprecedented study of identical twins looking into the effects of prolonged weightlessness.

CAPE CANAVERAL, Fla. — Astronaut Scott Kelly is gearing up for a one-year space station stint next spring. And his twin brother will be offering more than his usual moral support.

Retired astronaut Mark Kelly will be joining in from Earth. He'll undergo medical testing before, during and after his brother's American-record-setting flight.

It's part of an unprecedented study of identical twins, courtesy of the Kellys and NASA. Researchers hope to better understand how prolonged weightlessness affects the body, by comparing the space twin with the ground twin.

The 50-year-old NASA astronaut has volunteered to spend an entire year aboard the International Space Station beginning next March. He'll work the whole time alongside Russian cosmonaut Mikhail Kornienko.

The Russians are the masters of long-duration spaceflight, with a 14 ½-month mission to their credit.