“Our universe is a big place, and we have many millions of miles yet to explore. My departure from NASA is my next step on that journey,” Kelly said in a Facebook post.
Kelly, who turned 52 in February, returned from his year-long mission earlier this month, earning himself the American record for most time spent in space. He orbited the earth 5,440 times — traveling an estimated 143,846,525 miles — and conducted three spacewalks during that trip.
He also became something of a celebrity along the way. From space, Kelly appeared on early-morning and late-night television and posted hundreds of photos to Twitter, amassing more than 1 million followers.
But his primary mission was to help further NASA’s understanding of the effects of extended time in space on the human body.
“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,” Brian Kelly, director of Flight Operations at NASA’s Lyndon B. Johnson Space Center in Houston, said in a statement. Scott Kelly previously visited space in 1999, 2007 and 2010.
He joined the U.S. Navy in 1987 and NASA in 1996. And while he plans to retire in just a few weeks, Kelly said his will continue to work with the space agency.
“I remain ever committed and dedicated to the service of human exploration and advancement whether in space or on Earth,” he said. “… I will provide periodic medical samples and support other testing in much the same way that my twin brother, former astronaut Mark Kelly, has made himself available for the Twins Study throughout this past mission.”
Kelly was born in New Jersey in 1964 and is a graduate of the State University of New York Maritime College and the University of Tennessee in Knoxville.