Mission Twinpossible

The Kelly twins—one in orbit and one on Earth—may help NASA unlock the secrets of long-term space travel.

February 28, 2015

Mark, left, and Scott Kelly are identical twins.

When Scott Kelly calls home from the International Space Station (ISS) sometime this year, whoever answers the phone might simply hang up on him. The call will be welcome, but the connection can be bad. That can happen when you’re placing your call from 229 miles above the Earth. “When someone answers, I have to say, ‘It’s the space station! Don’t hang up!’” says Scott.

But his brother, Mark, knows the crackle of an extraterrestrial signal in his ear. Mark is a former astronaut who has been to space four times. Mark is also known for being married to former congresswoman Gabrielle Giffords, who was hurt in an assassination attempt in 2011.

Mark and Scott, 50, are identical twins. They have the same genetic makeup. Though they have served a combined seven missions, the brothers have never gone to space together.

A Year in Space

In March, Scott Kelly will leave his home in Houston, Texas, to spend one year aboard the ISS.

In March, Scott Kelly will leave his home in Houston, Texas, to spend one year aboard the ISS.

In March, Scott will leave his family in Houston, Texas, for a one-year stay aboard the ISS. It will set a single-mission record for a U.S. astronaut. Scott will share his marathon mission with Russian cosmonaut Mikhail Kornienko. A rotating cast of 13 other crew members will join them for shorter visits

The U.S. has long dreamed of sending astronauts to Mars. The biggest problem with reaching this goal is, simply, the human body. We are designed for Earth. In space, bones get brittle, eyeballs lose their shape, hearts beat less efficiently, and balance goes awry. “There’s quite a bit of data [on human health] for six months in orbit,” says space-station program manager Mike Suffredini. “Do things change at one year?”

NASA needs subjects to test the long-term effects of space. In a perfect experiment, every subject would have a control subject on Earth with the exact same genes. This would help scientists separate the changes that come from being in space from those that are a result of growing the same year older  on Earth. In the Kelly brothers—and only the Kelly brothers—NASA has that two-person sample group.

Star Twins

Scott’s days on the ISS will be packed with science experiments, exercise, and monitoring and fixing the station’s systems. The station is stocked with movies and books, and the crew can surf the Internet.

On this flight, Scott and Kornienko will be very closely monitored with medical and psychological tests. Mark will undergo similar study on the ground. Scientists hope that comparing the data will shed light on the impact of spending a long time in space.

Scott’s upcoming mission may be equal parts science experiment, endurance test, and human drama. To the Kelly brothers, it is just the latest mile in a journey they’ve shared for half a century.

TIME in Space

Scott Kelly is scheduled to soar into space later this month, and TIME For Kids will give you front-row seats to the entire mission.

Want to know what it’s like to pack  for a year away from Earth? Curious about the inner workings of a space suit? Interested in what it takes to train for a yearlong space mission?

Jonathan Woods, an editor at TIME, will be in close contact with Scott during his year in orbit. He will share the astronaut’s story as it unfolds. Follow along at, where we will share videos, photos, and blog posts throughout the historic mission.

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