Scott Kelly just spent a year in space - but his mission wasn't the longest ever

Scott Kelly holds the record for the longest consecutive time an American has spent in space at 340 days.

His Year in Space mission ends when he returns to Earth March 1, 2016.

But Kelly's trip is only the fourth-longest in history.

In short, Russian (and Soviet Union) cosmonauts totally kick our butts when it comes to long-duration spaceflight per person.

Check out how Kelly stacks up:

Russian cosmonaut Valeri Polyakov holds the all-time record at 437.7 days, which he completed almost two decades ago.

History reveals why cosmonauts have all the glory.

While NASA was busy sending astronauts to the moon, the USSR launched the world's first space station, Salyut 1, in 1971. They launched seven iterations of Salyut before putting the Mir station into orbit in 1986.

Cosmonaut Sergei Krikalev was in space so long that his country was the USSR when he left and Russia when he came back.

He went to space in May 1991; the Soviet Union dissolved in December, and Krikalev came back to Earth in March 1992.

The US launched Skylab, its first space station, in 1973. It remained in orbit until 1979.

And in 2000, the International Space Station (ISS) became the world's orbital outpost.

Since then, 221 people from 18 different countries have spent time in space aboard the ISS. And together they've performed almost 200 spacewalks, and conducted countless science experiments.

NASA's ultimate goal is to use the lessons learned from ISS missions like Scott Kelly's Year in Space to send astronauts to Mars - and soon. That journey will take about 2.5 years round-trip, so understanding spaceflight's effects on the human body will be even more important.

Humans have been in space since USSR cosmonaut Yuri Gagarin first orbited the Earth in 1961. And that was just the beginning.

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