Astronauts Mark Kelly, right, STS-124 commander, and Scott Kelly are pictured in the check-out facility at Ellington Field near NASA's Johnson Space Center in Houston.
Astronaut twins Mark and Scott Kelly will help NASA study the effects of spaceflight on the human body.
NASA announced Friday that the twin brothers will participate in 10 different investigations.
Craig Kundrot, deputy chief scientist of NASA's Human Research Program, says in a news release that the brothers provide a unique opportunity to study two people with the same genetics who were in different environments.
Officials say Scott Kelly spent a year in space while Mark Kelly was on Earth.
NASA says it is hoping the studies can be the basis for future research initiatives.
Mark Kelly is the husband of former U.S. Rep Gabrielle Giffords, who has been recovering after being shot in the head in 2011 in her home district of Tucson, Arizona.
He and Giffords are working on a book about gun control.