Space & Innovation

Astronaut Scott Kelly to Retire in April

Kelly is retiring after spending nearly a year in space and setting a record for the most cumulative days in space of any American.

Astronaut Scott Kelly will retire from NASA next month, after spending nearly a year in space and setting a record for the most cumulative days in space of any American, the US space agency said.

Kelly, a former Navy pilot who joined NASA in 1996, will leave the agency April 1.

"This year-in-space mission was a profound challenge for all involved, and it gave me a unique perspective and a lot of time to reflect on what my next step should be on our continued journey to help further our capabilities in space and on Earth," Kelly said in a statement.

Scott Kelly Reflects On His Incredible Year In Space

"I am humbled and excited by new opportunities for me to support and share the amazing work NASA is doing to help us travel farther into the solar system and work with the next generation of science and technology leaders."

He gave no further details on his plans post-retirement.

However, Kelly - who is allowing his body to be studied to further research on the effects of long-term spaceflight - will "continue to participate in the ongoing research related to his one-year mission," NASA said.

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"He will provide periodic medical samples and support other testing in much the same way that his twin brother, former astronaut Mark Kelly, made himself available for NASA's Twins Study during his brother's mission."

Kelly is a four-time veteran of spaceflight. His first trip was aboard the space shuttle Discovery in 1999, during a mission to repair NASA's Hubble Space Telescope. His other three missions were to the International Space Station.

His latest mission lasted 340 days, and gave him a US record of 520 cumulative days in space.

Kelly said he hoped the legacy of his near-year mission would be to help pave the way toward a deep space mission to Mars someday.

For now, the risks of long-term spaceflight remain unclear, amid concerns such as high radiation, food supply and the psychological challenges of spending months or years away from Earth.

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"When the first Americans set foot on Mars, they will be following in the footsteps of one of the finest astronauts in the history of the space program, my friend, Commander Scott Kelly," said NASA Administrator Charles Bolden.

"I can think of no one more deserving of some well-deserved rest and time on the same planet as his family and friends."

Expedition 46 Commander Scott Kelly of NASA rest in a chair outside of the Soyuz TMA-18M spacecraft just minutes after he and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos landed in a remote area near the town of Zhezkazgan, Kazakhstan.

Scott Kelly is a NASA astronaut working for a year in space on the International Space Station. Does he have the stuff of "The Martian,"

the highly anticipated Matt Damon movie to be released on Oct. 2

, chronicling the life of a stranded astronaut on the surface of Mars? While Kelly certainly isn't on his own in space, much of the work he is doing would be useful for a trip to Mars. Here are some of the things the astronaut is working on that Mark Watney (Damon's character in "The Martian") would appreciate.

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The sun goes through an 11-year cycle of activity, and we are just past the peak of one of those cycles. The solar peak is a time when the sun unleashes more flares and coronal mass ejections (charged particles). When these particles hit the Earth's magnetic field, they can produce spectacular auroras.

But they also can give astronauts a higher dose of radiation.

The space station monitors radiation levels for astronauts close to Earth; in fact, one of the reasons Kelly was selected for this mission was he did not exceed the lifetime radiation levels allowed for astronauts. Radiation is expected to jump for those travelling outside of Earth's magnetic influence. Mars doesn't have much magnetic field to speak of, and the Curiosity mission is monitoring radiation levels on the surface to get more information for future human missions.

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Working in space is a harsh business. You're busy all the time, you're stuck in a small environment with several people, and your family and friends are far away. NASA keeps close tabs on its astronauts' psychological health through measures such as doctor calls with astronauts, and

having the astronauts keep journals

during their missions. This will especially be important for Mars, as astronauts will need to be even more self-sufficient due to the time delay in communications between planets. NASA has

an ongoing comm delays study

for astronauts doing simple tasks; these tasks and their effects on astronauts will be studied as the station work continues.

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Microgravity is hard on your body. NASA has its astronauts exercise for a couple of hours a day, which seems to help counteract bone loss for missions of six months. But what about a year, or longer? That's part of what Kelly's mission is supposed to answer. Bones aren't the only things to worry about, either. Muscles shrink, eye pressure increases, your sense of balance changes. Even your immune system may be affected, something that

NASA is also looking at

in detail. So while we think of astronauts as boldly doing spacewalks and experiments on station, understand that they are also part of the experiment. Their very health is being watched for the benefit of future space missions.

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While Watney develops a certain affection for potatoes, Kelly recently posted a picture of himself looking pretty pleased next to a floating pile of fruit. It turns out that little comforts do go a long way for astronaut morale, and any nutritionist would tell you that a varied diet of healthy foods is good for you -- not just the freeze-dried stuff the Apollo astronauts survived on during their missions. NASA has an experiment in place to see how well

astronauts are meeting nutritional requirements for their work on station

, and also for their long-term health.

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Astronauts are very tied to shipments from Earth right now in terms of eating ... but that is changing in a small way.

Thanks to an experiment called Veggie

, astronauts got to taste some food grown aboard the space station this summer. Lettuce, of course, does not an entire meal make. But as the movie Contact (1997) reminds us, it's through "small moves" that we learn about science. The hope is eventually this experiment will translate into a better way of harvesting crops beyond Earth. For Mars, we're even wondering how viable the soil could be to support plants.

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"#ILookLikeAnEngineer on @space_station. Also a scientist, medical officer, farmer & at times a plumber," Kelly wrote with this image in August. What's more, he has to do all those things in a small space. Since every pound hoisted to space costs money, astronauts are accustomed to working in claustrophobic quarters. But NASA, concerned about its astronauts' efficiency and happiness, also has an

experiment that is supposed to look at how best to construct a living space for astronauts

. That way, the habitats designed for Mars will be suitable for long-term living.

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During a recent Twitter chat, Kelly was asked if he wanted to go to Mars. He said yes, as long as he could return. Getting to Mars and back will take hundreds of days of transportation, let alone the time on the surface. The gravity on Mars is less than 40% what we experience here on Earth. And unless spacecraft design changes substantially, the astronauts will be in microgravity on the way there and back. NASA has an experiment to see

how well (or badly) astronauts work on the surface shortly after landing

, an experiment that Kelly is participating in. This will be important not only for returning to Earth, but seeing how well a crew can get adapted to Mars after being in microgravity for the transit.

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