Twin brothers who used to be rivals and are now astronauts will head into space next year to make history.

Brothers Mark and Scott Kelly are finally putting their competition aside to work together during a space mission. They will be the first identical twins NASA has sent out on a mission together.

"I am not kidding you that we would fight every single day. We would fight -- fist fight until we were 15 years old. And our parents weren't home, so they would last eight hours," Mark Kelly said.

The two men have shared similar interests their entire lives. Both became naval officers out of college, traveled to space individually, and have worked together at NASA for more than 14 years.

"There are still people in the astronaut office who can't tell us apart," Scott Kelly said. "To be honest with you, it will be fun to be in space together. I feel l fortunate to have the privilege of flying in space and representing our country."

The Kelly twins will serve different roles on their historic mission. Scott will be the commander of the space station and Mark will serve as the commander of the final shuttle flight next year.