What happens to the human body after 340 days in orbit?

Space · Published 8 October 2026 Swipe more like this →

In short: To prepare for a journey to Mars, NASA needed to know how long-term spaceflight affects our biology. They sent Scott Kelly and Mikhail Kornienko into orbit for a record-breaking year. Their return marks a pivotal milestone in understanding the physiological and psychological toll of deep space.

To examine how extended voyages through space affect human physiology, NASA planned a vital twelve-month voyage as a precursor to Journey to Mars. While typical missions are much shorter, Kelly and Kornienko spent 340 days aboard the International Space Station (ISS). This duration allowed researchers to observe medical, physiological, and psychological performance challenges that cannot be fully captured in shorter stays.

The scientific rigor of the mission began a full year before launch. Researchers collected biological samples and performed assessments to establish baseline data for both astronauts. To increase the precision of these findings, NASA conducted parallel twin studies on Earth involving Scott Kelly's identical twin brother, former astronaut Mark Kelly. This provided scientists with a unique control group to compare against the physiological changes occurring in orbit.

The mission concluded on March 1, 2016, with a safe parachute landing in Kazakhstan. The data gathered during this year-long stay will be analyzed for at least one more year following their return. By monitoring these changes over such an extended period, NASA aims to develop the necessary countermeasures to keep humans healthy during the multi-year voyages required for interplanetary exploration.

Following the conclusion of the one-year crew's mission, command of the ISS was handed over to Tim Kopra as part of Expedition 47. This transition highlights the continuous nature of orbital research, where new crews immediately begin building on the data provided by long-duration pioneers.

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