Expedition 46 Commander Scott Kelly of NASA rest in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan on Wednesday, March 2, 2016 (Kazakh time). Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. Photo Credit: (NASA/Bill Ingalls)
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Scott Kelly's year in space
01:30 - Source: CNN

Story highlights

His retirement will take effect April 1

Scott Kelly went to space four times, spending a total of 520 days

He will continue to work with NASA, which is studying the effects of his last voyage

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”

CNN’s John Newsome contributed to this report.