A year in orbit: testing the limits of human biology

Space · Published 8 October 2026 Swipe more like this →

In short: How does a human body react to a full year of weightlessness? NASA and Roscosmos sent two astronauts into orbit to find out. Their mission serves as a critical blueprint for the future of human exploration, specifically the grueling journey to Mars.

On March 27, NASA astronaut Scott Kelly and Roscosmos cosmonaut Mikhail Kornienko launched on a mission to the International Space Station. While many space missions last weeks or months, this specific expedition was designed to last a full year. The primary objective was to conduct extensive biomedical research to understand how long-duration spaceflight affects human physiology and genetics. These findings are considered essential for formulating the requirements of future crewed missions to Mars. What makes this specific study unique is the use of a biological control group: Scott Kelly's identical twin brother, Mark Kelly. Because they share the same genetic makeup, doctors can monitor Scott's body while he is in orbit and compare the data against Mark, who remains on Earth.

This allows researchers to isolate the effects of space travel from genetic variables. Throughout the mission, doctors monitored Scott for any significant changes in his physical health, while Mark even joked about the importance of providing regular urine and stool samples for the study. The mission was documented extensively by Time Magazine, which expanded a simple print story into a 10-part documentary series. The series captured the personal toll of the mission, including interviews with Scott's family and his girlfriend, as well as the clinical side of the research. By the time the midway point was reached on September 15, the crew had already spent 125 days in space, providing a massive dataset on human endurance in microgravity.

The significance of this research lies in the transition from short-term orbital stays to deep-space travel. Every hour spent in space presents unique challenges to the human body, and a year-long stay provides a much more comprehensive look at cumulative degradation and adaptation. By studying the Kelly twins, scientists can better predict how astronauts might age, lose bone density, or experience muscle atrophy during the multi-month transit to the Red Planet. This data is the foundation for the next era of human spaceflight.

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