Scott Kelly
Scott Kelly inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the space stationNASA/Reuters

Astronaut Scott Kelly returned to Earth on Wednesday 2 March. His landing signified the end of a mission lasting 340 days – the longest amount of time any American has spent in space without at least one trip home.

His mission began on 27 March 2015, when he journeyed into space along with his Russian partner, Mikhail Kornienko.

In total, Kelly has now spent 520 days in space - including previous missions. That makes him the US astronaut who has spent the most time away from Earth.

Kelly's mission was to explore how the body is affected by being in space. That includes weightlessness, radiation and isolation.

For example, one of the research projects Kelly took part in was to examine the effect of fluids moving through the body in space. Whilst weightless, these fluids tend to move into the upper body, and that can cause a build up of pressure inside the head causing vision problems

To correct this, the scientists tested the use of Russian chibis devices - a suit which looks like a mechanical pair of trousers. This device pulls the fluids towards the legs of the astronaut, mimicking gravity on Earth.

Kelly took part in nearly 400 experiments whilst on board the International Space Station - all of which helped Nasa explore how life would survive living on Mars.

He also ventured out of the ISS on three separate space walks. These were to carry out ISS maintenance, fixing the mobile transporter system on board, and also reconfiguring an ammonia cooling system.

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Scott Kelly and Terry Virts work on a Carbon Dioxide Removal Assembly (CDRA) inside the Japanese Experiment ModuleNASA/Reuters
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Scott Kelly enjoys his first drink from the new ISSpresso machine. The espresso device allows crews to make tea, coffee, broth, or other hot beverages they might enjoyNASA/Reuters
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Scott Kelly is shown with flight engineer Sergey VolkovNASA/Reuters
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Scott Kelly watches a bunch of fresh carrots float in front of him during snack timeNASA/Reuters
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Scott Kelly while watching his twin brother Mark Kelly's appearance on JeopardyNASA/Reuters
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Scott Kelly corrals the supply of fresh fruit that arrived on the Kounotori 5 H-II Transfer Vehicle. Visiting cargo ships often carry a small cache of fresh food for crew members aboard the International Space StationNASA/Reuters
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Scott Kelly as he prepares a scientific experimentNASA/Reuters
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Scott Kelly has his morning coffee and TV news from the Houston areaNASA/Reuters
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Scott Kelly during a spacewalk in which Kelly and Flight Engineer Tim Kopra successfully moved the International Space Station's mobile transporter rail car ahead of a docking of a Russian cargo supply spacecraftNASA/Reuters
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The International Space Station Expedition 45 crew gathers inside the Destiny laboratory to celebrate the 15th anniversary of continuous human presence aboard the International Space StationNASA/Reuters

Kelly returned home in the Soyuz TMA-18M spacecraft, also carrying Russian cosmonauts Sergei Volkov and Mikhail Korniyenko. They landed near the town of Zhezkazgam, Kazakhstan, at 04.26 am GMT.

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The Soyuz TMA-18M spacecraft carrying International Space Station (ISS) crew members U.S. astronaut Scott Kelly, Russian cosmonauts Sergei Volkov and Mikhail Korniyenko descends shortly before landing near the town of Dzhezkazgan (Zhezkazgan), KazakhstanNASA/Reuters
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Ground personnel help U.S. astronaut Scott Kelly to get out of a Soyuz capsule shortly after landingNASA/Reuters
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Ground personnel carry U.S. astronaut Scott Kelly shortly after landingNASA/Reuters
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U.S. astronaut Scott Kelly is assisted by ground personnel shortly after landingNASA/Reuters
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U.S. astronaut Scott Kelly (R) and Russian cosmonauts Sergei Volkov (C) and Mikhail Korniyenko, surrounded by ground personnel, rest shortly after landingNASA/Reuters