(CNN) Scott Kelly, the astronaut who spent a U.S. record 520 days in four flights in space, will retire April 1, NASA announced Friday.
Kelly, who just returned from a 340-day mission that included time on the International Space Station, will continue to be a part of the study of his nearly one-year assignment.
"This year-in-space mission was a profound challenge for all involved, and it gave me a unique perspective and a lot of time to reflect on what my next step should be on our continued journey to help further our capabilities in space and on Earth," Kelly said.
Kelly, 52, began his astronaut career in 1996. He was a shuttle pilot on STS-103 in 1999 and was the mission commander for STS-118 in 2007.
He spent 159 days on the space station from October 2010 to March 2011.
His recent trip took him 143,846,525 miles around Earth.
"My career with the Navy and NASA gave me an incredible chance to showcase public service to which I am dedicated, and what we can accomplish on the big challenges of our day," Kelly said.
He and his twin, Mark, are the only brothers ever to travel in space.
"Scott's contributions to NASA are too many to name," said Brian Kelly, director of flight operations at NASA's Johnson Space Center in Houston. "In his year aboard the space station, he took part in experiments that will have far-reaching effects, helping us pave the way to putting humans on Mars and benefiting life on Earth."
Last week Scott Kelly said he doubted he would ever fly again for NASA but that didn't mean he wouldn't think about going up again.
"I don't think I would ever say I'm absolutely 100% done because I think there's a lot of exciting possibilities out there, maybe in the commercial aspect, certainly," he told reporters. "They might need a guy like me someday."
And even if he doesn't fly, he said he still will be involved in some way.
"I'll never be done with space," he said.
In a blog post Friday, Kelly said he looks forward to supporting NASA's work as it travels farther into space.
Scott Kelly: "Going to Mars is doable"