After returning to Earth from spending almost a year in space, NASA astronaut Scott Kelly announced that he will be finally retiring. The veteran astronaut landed on Earth last week with fellow Russian cosmonaut Mikhail Kornienko after spending 340 days at the International Space Station in lower Earth orbit.

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Kelly is scheduled to leave the space agency beginning April 1 where he is the first American astronaut to hold the record number of cumulative days in space. The 52 year old Kelly joined NASA in 1996 where he believes that this successful mission of his will be crucial for future manned missions to Mars. The retired astronaut is still expected to work during an ongoing research about his space mission, that will take a series of yearlong tests.

His first ever space mission was in 1991 during the a Space Shuttle mission where the Discovery shuttle arrived at NASA's Hubble Space Telescope in lower Earth orbit. Kelly's missions include this servicing mission along with three other missions. Before this almost one year mission, Kelly spent 159 days on the orbiting space laboratory. 

Kelly, who is also a former navy pilot, is the first one to break this record set by a former astronaut, Michael Lopez-Alegria, who spent 215 days at the space station in 2007. Kelly reveals that the hardest challenge of being up in the ISS for 340 days straight was being away from family and friends.

Kelly reflects upon his last space mission where he was a member of the one year crew, saying that this year long mission was a profound challenge indeed and for all those who are involved. It also gave a unique perspective and a lot of time for reflection on which next step to take to the continuing journey of humans and developing capabilities for space travel and on Earth.

During his stay, Kelly also captured numerous stunning images of space and Earth's view from space. He also released videos of him playing table tennis with water on his official Twitter account. 

The main focus of Kelly's space mission is for mission scientists to study the effects of space's harsh environment on the human body where the veteran astronaut allowed himself to be observed and studied, to further understand the effects of microgravity and long term space flights on the body and mind. He reported having underwent significant physical changes where he even added two inches to his height.

In the meantime, back on Earth, Kelly's twin brother, Mark Kelly, who is also a former NASA astronaut, is also working on the same tests and studies on his body to compare with Scott Kelly's exposure to space and radiation on NASA's Twins Study.