NASA: Astronaut Scott Kelly to retire after year-in-space mission

Astronaut Scott Kelly, recently back on land after a stint on the International Space Station, is retiring, NASA announced Friday.

Kelly's retirement takes effect April 1, NASA said. Kelly, who now holds the record for the most consecutive days spent in space by an American, returned to Earth March 1 by way of Kazakhstan and arrived in Houston two days later.

NASA's Scott Kelly is back in the U.S., after a year in space

"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 in a statement. "I am humbled and excited by new opportunities for me to support and share the amazing work NASA is doing to help us travel farther into the solar system and work with the next generation of science and technology leaders.”

During his year aboard the International Space Station, Kelly took part in a study on twins, involving his own twin brother, former astronaut Mark Kelly. The purpose of the study is to figure out the effects of space on the human body.

In a posting to Facebook on Friday, Kelly announced his retirement and said his relationship with science and the great beyond was not ending.

"Following my retirement, I will continue to participate in the ongoing research related to NASA’s one-year mission for as long as is necessary," Kelly wrote. "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."

Awe-inspiring photos from Scott Kelly's year in space

During his career, Kelly ventured into space four times. The first trip took place in 1999, when he went on the shuttle Discovery trip to NASA's Hubble Telescope.

NASA administrator Charles Bolden hailed Kelly and his astronaut career.

"When the first Americans set foot on Mars, they will be following in the footsteps of one of the finest astronauts in the history of the space program, my friend, Commander Scott Kelly," Bolden said in a statement. "After spending an American record 520 days in space – including his Year in Space – I can think of no one more deserving of some well-deserved rest and time on the same planet as his family and friends."

In his Facebook post, Kelly said he's traveled 146,846,525 miles around the globe in the International Space Station mission and that he was grateful for his time and experiences with NASA.

"I look forward to continuing my 30 years of public service in a new role," Kelly wrote. "To continue toward any journey, we must always challenge ourselves to take the next step."