Scott Kelly: What It’s Like To Live In Space

You’ve likely heard of Scott and Mark Kelly, the American astronauts—and identical twins—who have collectively logged nearly 600 days in space. But did you know that their final mission, to compare the long-term effects of life in space (Scott) with that of a genetic twin on Earth (Mark), could provide information that’s vital to sending humans to Mars and beyond?

Begun in 2014, the “Twins Study” for NASA’s Human Research program is just starting to generate information (the first post-flight data was released this year). “Science progresses slowly,” notes Dr. John Charles, who heads the study for NASA. “It isn’t like what you see on TV.”

Still, it’s expected that the comparative analysis of the Kelly twins will provide a flood of findings about how prolonged exposure to zero gravity, radiation and cramped quarters affect the human body. Researchers hope those insights will help us prepare for space trips planned by government agencies like NASA, as well as private enterprises. Here’s the 411 so far:

Scott’s Post-Flight Checkup

A Bit Spacey

Having logged nearly 144 million miles over 520 days in space, Scott grew so accustomed to life in zero gravity, he felt uncoordinated back on terra firma. When he tried shooting hoops—a favorite hobby—at first Scott missed every shot.

Far-Out Views

Between space-walks, Scott posted hundreds of stunning images of Earth, which gained him more than 3 million followers on social media.

NASA astronaut Scott Kelly was the commander of Expedition 46 to the International Space Station, a 340-day mission from 2015 to 2016. Here he sits in the space station’s cupola, which had a 360-degree view of Earth.

Kelly posted this photo of a moonrise from the International Space Station on social media on July 17, 2015 with the caption: “Day 112. #Moonrise is upon us.”

Kelly, shown here on a spacewalk to get ready for the docking of a Russian supply cargo spacecraft.

Enjoying the fruits of labor, literally, in zero gravity on the International Space Station.

Kelly posted this photo taken from the International Space Station on social media on September 5, 2015 with the caption: “#goodnight #Earth! Make me proud and I'll try and do the same. #YearInSpace.”

Clear skies over the United States, photographed by Kelly, during an early morning flyover on September 17, 2015.

Returning home after an earlier mission in 2011. Kelly spent six months on the International Space Station with Russian cosmonauts.

Kelly stands in the Japanese Experiment Module, holding a sign with the hashtag #whyspacematters, part of a global photography competition.

That’s A Stretch

Scott grew nearly two inches taller while on the International Space Station. Without gravity’s pull, his spine expanded—temporarily. Back on Earth, his height—and presumably his ability to dunk a basketball—will return to normal.

Relatively Younger

Circling Earth at 17,500 m.p.h. for a year made Scott younger by five milliseconds—intriguing evidence of Einstein’s theory that the faster you move, the more time (for you) slows down.

Thin Skin

Scott’s skin burned when he first sat and walked on solid ground because his body was no longer used to the friction we Earthlings experience every day.

Mark’s Condition On the Ground

In Control

Having retired in 2011 after 54 days in space to his credit, Scott’s twin served as the study’s Earth-bound “control.” Mark supplied NASA with blood, urine, saliva and other samples to compare with his brother’s.


In 2007, Mark Kelly married then-U.S. Congresswoman Gabrielle Giffords. After the attempt on Giffords’ life, the two co-wrote a memoir: Gabby: A Story of Courage, Love and Resilience about the experience.

Still Older

Einstein or not, Mark remains the older twin by his original six minutes—plus Scott’s newfound five milliseconds.

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By Rosa Harris