Scott Kelly Biography: NASA Astronaut & One-Year Space Mission

Scott Kelly is a retired American NASA astronaut, engineer, naval aviator, and test pilot best known for spending 340 consecutive days aboard the International Space Station (ISS) during NASA's historic One-Year Mission.

A veteran of four spaceflights, Kelly flew aboard the Space Shuttle Discovery, commanded Space Shuttle Endeavour, served as commander of the International Space Station, and later spent nearly a year in orbit alongside Russian cosmonaut Mikhail Kornienko. By the end of his NASA career, Kelly had accumulated approximately 520 days in space, making him the American astronaut with the most cumulative time in space at the time of his retirement.

His year in orbit was particularly important because it was accompanied by the NASA Twins Study. While Scott Kelly lived aboard the ISS, his identical twin brother and fellow former astronaut Mark Kelly remained on Earth. Scientists compared the brothers before, during, and after the mission to investigate how long-duration spaceflight affects the human body.

The mission provided NASA with important information about human adaptation to space and helped prepare researchers for future missions that could take astronauts beyond low Earth orbit to destinations such as the Moon and Mars.

Scott Kelly Quick Facts

Category	Details
Full Name	Scott Joseph Kelly
Born	February 21, 1964
Birthplace	Orange, New Jersey, USA
Nationality	American
Profession	Retired NASA Astronaut, Engineer, Naval Aviator, Test Pilot
Military Branch	United States Navy
NASA Selection	1996
Astronaut Group	NASA Group 16
Spaceflights	4
First Spaceflight	STS-103
Second Spaceflight	STS-118
Third Spaceflight	Expedition 25/26
Fourth Spaceflight	One-Year Mission, Expeditions 43–46
Total Time in Space	About 520 days
Longest Mission	340 days
ISS Command	Expeditions 26, 45 and 46
Spacewalks	3 during his final mission
Identical Twin	Mark Kelly
NASA Retirement	2016
Major Research Program	NASA Twins Study

NASA records that Kelly completed four spaceflights and accumulated more than 520 days in space. He retired from NASA in 2016 after completing the historic yearlong mission.

Scott Kelly's Education and Early Career

Scott Kelly's path toward becoming an astronaut began with his interest in aviation and engineering.

He attended the State University of New York Maritime College, where he earned a Bachelor of Engineering degree in Electrical Engineering and Marine Engineering. He later completed a master's degree in aviation systems at the University of Tennessee, Knoxville.

His education gave him a strong technical foundation, but his professional career soon moved toward military aviation.

Kelly joined the United States Navy, where he trained as a naval aviator and eventually became a highly experienced fighter pilot and test pilot.

NASA's biography records that he accumulated more than 8,000 hours in more than 40 different aircraft and spacecraft and completed more than 250 aircraft carrier landings.

This extensive aviation background eventually became one of the reasons he was selected for NASA's astronaut corps.

Scott Kelly as a Navy Fighter Pilot

As a naval aviator, Kelly flew high-performance military aircraft and gained experience operating in demanding environments.

He later became a test pilot, a role requiring pilots to evaluate aircraft performance, systems, and handling characteristics under carefully controlled conditions.

Test pilots must combine flying ability with engineering knowledge because they often collect and analyze technical information while operating experimental or modified aircraft.

This combination of engineering, aviation, military discipline, and technical analysis made Kelly well suited to NASA's astronaut program.

He eventually retired from the U.S. Navy as a captain in June 2012, although by that time his career had already moved from naval aviation to spaceflight.

Scott Kelly Becomes a NASA Astronaut

In April 1996, NASA selected Scott Kelly as a member of its 16th astronaut class.

He reported to NASA's Johnson Space Center in Houston in August 1996 and began the extensive training required to become a Space Shuttle and International Space Station astronaut.

His training included spacecraft systems, spacewalking procedures, robotics, survival skills, flight operations, and other technical disciplines required for human spaceflight.

After completing his initial training, Kelly worked in NASA's Astronaut Office on spacecraft systems and operations.

He also later served as NASA's Director of Operations at Star City, Russia, supporting U.S. astronaut operations and training associated with the Russian space program.

This international experience would become especially relevant later in his career because his longest space mission was a joint U.S.-Russian effort.

Scott Kelly's First Spaceflight: STS-103

Scott Kelly's first journey into space took place in December 1999 aboard Space Shuttle Discovery.

The mission was STS-103, a servicing mission to the Hubble Space Telescope.

Kelly served as the shuttle's pilot.

The mission lasted approximately eight days and focused on repairing and upgrading the Hubble Space Telescope so that it could continue conducting scientific observations of the universe.

STS-103 included three spacewalks and completed 120 orbits of Earth, traveling approximately 3.2 million miles.

For Kelly, the mission marked the beginning of a spaceflight career that would eventually include four missions and more than 500 days in orbit.

Scott Kelly and Space Shuttle Endeavour

Kelly's second spaceflight came in August 2007 aboard Space Shuttle Endeavour.

The mission, STS-118, traveled to the International Space Station.

This time, Kelly served as the mission commander.

Endeavour delivered equipment and supplies to the ISS and installed an additional truss segment, a gyroscope, and an external spare-parts platform. The mission also involved four spacewalks conducted by three crew members.

STS-118 lasted approximately 12 days, 17 hours and 55 minutes and covered about 5.3 million miles.

The mission represented a major step in Kelly's career because it gave him experience commanding a complex human spaceflight mission.

Scott Kelly's First Long-Duration ISS Mission

Kelly returned to space in October 2010, this time beginning a long-duration mission aboard the International Space Station.

He launched aboard the Soyuz TMA-M spacecraft and became a member of Expedition 25.

Later, he became commander of Expedition 26.

Kelly spent approximately 159 days aboard the ISS during this mission.

The experience prepared him for his most ambitious mission yet: NASA's One-Year Mission.

Scott Kelly's Historic One-Year Mission

The most important chapter in Scott Kelly's space career began on March 27, 2015.

Kelly and Russian cosmonaut Mikhail Kornienko launched toward the International Space Station for a mission designed to last approximately one year.

They eventually spent 340 days aboard the ISS, returning to Earth on March 2, 2016.

The mission was significantly longer than the typical six-month ISS expedition.

Its primary purpose was to help scientists understand how the human body responds to the physical and psychological demands of extended spaceflight.

This was particularly important because future missions to Mars could require astronauts to spend years away from Earth.

Why Scott Kelly Spent a Year in Space

Living in space for a year is very different from spending a few days or weeks in orbit.

Long-duration spaceflight exposes astronauts to challenges such as:

• Microgravity

• Radiation

• Changes in muscles and bones

• Altered vision

• Psychological isolation

• Changes to the immune system

• Sleep and circadian-rhythm disruption

• Limited medical support

• Long periods away from Earth

NASA therefore used Kelly's mission to conduct a large collection of scientific investigations.

Kelly and Kornienko participated in 23 investigations across seven research disciplines, providing information about the effects of long-duration spaceflight on the human body and mind.

Scott Kelly and the NASA Twins Study

One of the most remarkable aspects of Kelly's yearlong mission was that he had an identical twin brother who was also a former astronaut.

While Scott Kelly spent 340 days in space, Mark Kelly remained on Earth.

This created an extraordinary scientific opportunity.

Because identical twins share virtually the same genetic background, scientists could compare the biological changes experienced by Scott during spaceflight with measurements from Mark on Earth.

The research became known as the NASA Twins Study.

Ten research teams collaborated on the project, examining physiological, molecular, behavioral, cognitive, genetic, and microbiological changes associated with long-duration spaceflight.

It was one of the most comprehensive investigations ever conducted into the effects of spaceflight on a single human being.

What Did the Twins Study Discover?

The NASA Twins Study found that the human body is remarkably resilient during and after long-duration spaceflight, although researchers observed numerous changes at the molecular, cellular, physiological, and cognitive levels.

Researchers observed changes involving areas such as:

• Gene expression

• Immune-system activity

• Gut microbiome

• Metabolism

• Cardiovascular function

• Cognitive performance

• Telomeres

• Inflammation

Importantly, NASA clarified that Scott Kelly's DNA itself did not fundamentally change. Some changes occurred in gene expression, which describes how genes respond to environmental conditions.

The findings helped scientists understand which changes occur during spaceflight and which tend to return toward normal after an astronaut comes back to Earth.

Scott Kelly's 340 Days in Orbit

Kelly's One-Year Mission lasted 340 days, making him the first American astronaut to spend approximately a year continuously in space.

During the mission, he and his crew conducted hundreds of experiments and scientific investigations.

NASA records that Kelly completed approximately 5,440 orbits of Earth during the yearlong mission.

From the ISS, he also photographed Earth extensively.

His photographs became famous for showing the planet's landscapes, oceans, deserts, cities, mountains, clouds, and atmospheric phenomena from orbit.

These images helped communicate the beauty and interconnectedness of Earth to millions of people.

Scott Kelly's Spacewalks

During his final mission, Kelly completed three spacewalks.

The activities included station maintenance and upgrades that helped prepare the ISS for future spacecraft and improve station systems.

One spacewalk involved routing cables to prepare for new docking ports for U.S. commercial crew spacecraft.

Another involved work on the station's ammonia cooling system and helped restore the station's solar-power-generating capability.

The third spacewalk involved work on the station's Mobile Transporter system.

These tasks demonstrate that long-duration astronauts are not simply passengers or laboratory researchers. They are also responsible for maintaining and upgrading the complex spacecraft in which they live.

Scott Kelly and International Cooperation

The One-Year Mission was a major example of international cooperation in space exploration.

Kelly worked closely with Russian cosmonaut Mikhail Kornienko, and the ISS crew represented multiple countries.

During the yearlong mission, 13 astronauts and cosmonauts from seven nations lived aboard the station at different points.

This international environment demonstrated how space exploration can bring together nations with different languages, cultures, and political systems around shared scientific and technological goals.

Scott Kelly's Spaceflight Record

When Kelly completed his One-Year Mission, he had accumulated approximately 520 days in space across four missions.

NASA noted that he broke the American record for cumulative time in space during the mission.

It is important to distinguish this historical record from the current record. Kelly's achievement was extraordinary, but other astronauts later surpassed his total time in space.

His more enduring contribution is the scientific value of his long-duration mission and the Twins Study.

Scott Kelly Retires From NASA

Scott Kelly retired from NASA effective April 1, 2016, shortly after returning from his yearlong mission.

His retirement marked the end of a NASA career spanning approximately two decades.

However, his involvement in scientific research did not end when he left the astronaut corps.

Kelly continued participating in research connected to the One-Year Mission and provided medical samples and other information required for the ongoing Twins Study.

Scott Kelly as an Author and Photographer

After his astronaut career, Kelly continued sharing his experiences through books and public appearances.

His memoir Endurance: A Year in Space, A Lifetime of Discovery describes his life, military career, astronaut training, and year aboard the ISS.

He also published Infinite Wonder: An Astronaut's Photographs from a Year in Space, showcasing photographs taken during his time aboard the ISS. His official website lists these books alongside other works, including a young readers' edition of Endurance.

His photography has become an important part of his public legacy because it gives people on Earth a visual perspective of the planet from orbit.

Scott Kelly and Earth Observation

One of the most visually memorable parts of Scott Kelly's career was his photography of Earth from the International Space Station.

From approximately 400 kilometers above the planet, familiar geographic features appear in completely different ways.

Mountain ranges, coastlines, deserts, rivers, agricultural patterns, cities, ice sheets, and clouds can reveal patterns that are difficult to appreciate from the ground.

Kelly's images therefore provide more than beautiful photographs. They offer a different way of thinking about Earth's geography.

From orbit, national borders are generally invisible. Instead, the planet appears as one interconnected system of land, water, atmosphere, and life.

Scott Kelly and the Future of Mars Exploration

The One-Year Mission was designed partly as preparation for future human exploration beyond low Earth orbit.

A crewed mission to Mars would be dramatically longer than a typical ISS expedition.

NASA's research from Kelly's mission therefore focused on understanding the challenges of long-duration human spaceflight.

The Twins Study specifically described Kelly's year in space as a stepping stone toward missions such as a three-year round trip to Mars.

Research from Kelly's mission continues to contribute to NASA's broader understanding of how humans can remain healthy during extended missions.

Scott Kelly's Connection to Geography

Scott Kelly's career has a particularly strong relationship with geography because much of his public legacy involves seeing Earth from space.

Before becoming an astronaut, Kelly's work was focused on aviation and spacecraft.

Once aboard the ISS, however, he gained an entirely different relationship with the planet.

During his year in space, he completed thousands of orbits and repeatedly watched Earth pass beneath him.

He observed:

• Continents

• Oceans

• Mountain ranges

• Deserts

• Rivers

• Cities

• Polar regions

• Storm systems

• Atmospheric phenomena

His photographs helped show how Earth's physical geography appears when viewed from orbit.

Kelly's career can therefore be represented as:

Earth → Aviation → Space Shuttle → International Space Station → Global Earth Observation → Future Mars Exploration

His story demonstrates that geography is not limited to maps on a classroom wall. From space, astronauts experience geography on a planetary scale.

Explore More Geography With GeoMapGame

Scott Kelly spent hundreds of days looking down at Earth from orbit, observing the planet's continents, oceans, landscapes, cities, and geographic patterns from a completely different perspective.

If you enjoy exploring countries, capitals, continents, landmarks, maps, and geographical facts, you can discover more geography challenges on GeoMapGame.

It is a fun way to test your geographical knowledge and explore the world from a new perspective.

Scott Kelly's Major Achievements

Four Spaceflights

Scott Kelly completed four space missions between 1999 and 2016, including Space Shuttle missions and long-duration ISS expeditions.

340-Day One-Year Mission

He spent 340 consecutive days aboard the ISS during NASA's One-Year Mission with Mikhail Kornienko.

About 520 Days in Space

By the end of his career, Kelly had accumulated approximately 520 days in space, setting an American cumulative spaceflight record at the time.

ISS Commander

Kelly commanded multiple International Space Station expeditions, including Expeditions 26, 45 and 46.

NASA Twins Study

His year in space enabled NASA's landmark Twins Study, comparing Scott's biological changes in orbit with those of his identical twin brother Mark on Earth.

Hubble Space Telescope Mission

His first spaceflight, STS-103, involved servicing and upgrading the Hubble Space Telescope.

Extensive Aviation Experience

Kelly accumulated more than 8,000 flight hours across more than 40 aircraft and spacecraft and completed more than 250 carrier landings.

Scott Kelly Career Timeline

Year	Milestone
1964	Born in Orange, New Jersey
1980s	Studied engineering and entered naval aviation
1996	Selected by NASA as an astronaut
1999	Flew first mission, STS-103, to service Hubble
2007	Commanded Space Shuttle Endeavour on STS-118
2010	Began long-duration ISS mission
2011	Commanded Expedition 26
2012	Retired from the U.S. Navy
2015	Began NASA's One-Year Mission aboard the ISS
2016	Returned after 340 days in space
2016	Retired from NASA
2019	NASA published major integrated findings from the Twins Study
After NASA	Continued writing, public speaking, photography and science outreach

Frequently Asked Questions About Scott Kelly

Who is Scott Kelly?

Scott Kelly is a retired NASA astronaut, engineer, former U.S. Navy captain, naval aviator, and test pilot who completed four spaceflights and spent approximately 520 days in space.

What is Scott Kelly famous for?

Scott Kelly is best known for spending 340 consecutive days aboard the International Space Station during NASA's One-Year Mission and participating in the landmark Twins Study with his identical twin brother, Mark Kelly.

How long did Scott Kelly stay in space?

Scott Kelly spent 340 consecutive days aboard the ISS during his One-Year Mission. Across all four spaceflights, he accumulated approximately 520 days in space.

How many times did Scott Kelly go to space?

Scott Kelly flew to space four times: STS-103 in 1999, STS-118 in 2007, an ISS expedition beginning in 2010, and the One-Year Mission beginning in 2015.

What was the NASA Twins Study?

The NASA Twins Study compared Scott Kelly, who spent nearly a year in space, with his identical twin brother Mark Kelly, who remained on Earth. Scientists used the unusual genetic similarity between the brothers to study how long-duration spaceflight affects the human body.

Is Scott Kelly still a NASA astronaut?

No. Scott Kelly retired from NASA in April 2016 after completing his One-Year Mission.

How many spacewalks did Scott Kelly complete?

Kelly completed three spacewalks during his 340-day One-Year Mission.

Who is Scott Kelly's twin brother?

Scott Kelly's identical twin brother is Mark Kelly, who is also a former NASA astronaut. Mark remained on Earth during Scott's 340-day mission and served as the comparison subject for the NASA Twins Study.

Did Scott Kelly help prepare NASA for Mars missions?

Yes. NASA designed the One-Year Mission and associated research to better understand the effects of long-duration spaceflight and to help prepare for future missions beyond low Earth orbit, including potential human missions to Mars.

Conclusion

Scott Kelly's biography is a story of aviation, engineering, space exploration, scientific research, and endurance.

His career began with engineering and naval aviation before taking him into NASA's astronaut corps. Across four spaceflights, he flew to the Hubble Space Telescope, commanded a Space Shuttle mission, led International Space Station expeditions, and ultimately spent 340 consecutive days in orbit.

His final mission became particularly significant because it transformed his own body into an important subject of scientific research. By comparing Scott with his identical twin brother Mark, NASA scientists gained a rare opportunity to study the effects of long-duration spaceflight on a human being.

Scott Kelly's story is therefore about more than a record number of days in space. His mission helped answer fundamental questions about how humans adapt to living away from Earth and provided knowledge that could support future exploration of the Moon, Mars, and beyond.

From flying Navy aircraft to commanding spacecraft and watching Earth from orbit, Scott Kelly's career represents one of the most important chapters in the history of long-duration human spaceflight.

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Meta Title: Scott Kelly Biography: NASA Astronaut & One-Year Space Mission

Meta Description: Explore Scott Kelly's biography, including his Navy career, four spaceflights, 340-day ISS mission, NASA Twins Study, spacewalks and contribution to future Mars exploration.

Image Alt Text:Scott Kelly Biography: NASA Astronaut, Navy Pilot & One-Year Space Mission Pioneer

Scott Kelly is a retired American NASA astronaut, engineer, naval aviator, and test pilot best known for spending 340 consecutive days aboard the International Space Station (ISS) during NASA's historic One-Year Mission.

A veteran of four spaceflights, Kelly flew aboard the Space Shuttle Discovery, commanded Space Shuttle Endeavour, served as commander of the International Space Station, and later spent nearly a year in orbit alongside Russian cosmonaut Mikhail Kornienko. By the end of his NASA career, Kelly had accumulated approximately 520 days in space, making him the American astronaut with the most cumulative time in space at the time of his retirement.

His year in orbit was particularly important because it was accompanied by the NASA Twins Study. While Scott Kelly lived aboard the ISS, his identical twin brother and fellow former astronaut Mark Kelly remained on Earth. Scientists compared the brothers before, during, and after the mission to investigate how long-duration spaceflight affects the human body.

The mission provided NASA with important information about human adaptation to space and helped prepare researchers for future missions that could take astronauts beyond low Earth orbit to destinations such as the Moon and Mars.

Scott Kelly Quick Facts

Category	Details
Full Name	Scott Joseph Kelly
Born	February 21, 1964
Birthplace	Orange, New Jersey, USA
Nationality	American
Profession	Retired NASA Astronaut, Engineer, Naval Aviator, Test Pilot
Military Branch	United States Navy
NASA Selection	1996
Astronaut Group	NASA Group 16
Spaceflights	4
First Spaceflight	STS-103
Second Spaceflight	STS-118
Third Spaceflight	Expedition 25/26
Fourth Spaceflight	One-Year Mission, Expeditions 43–46
Total Time in Space	About 520 days
Longest Mission	340 days
ISS Command	Expeditions 26, 45 and 46
Spacewalks	3 during his final mission
Identical Twin	Mark Kelly
NASA Retirement	2016
Major Research Program	NASA Twins Study

NASA records that Kelly completed four spaceflights and accumulated more than 520 days in space. He retired from NASA in 2016 after completing the historic yearlong mission.

Scott Kelly's Education and Early Career

Scott Kelly's path toward becoming an astronaut began with his interest in aviation and engineering.

He attended the State University of New York Maritime College, where he earned a Bachelor of Engineering degree in Electrical Engineering and Marine Engineering. He later completed a master's degree in aviation systems at the University of Tennessee, Knoxville.

His education gave him a strong technical foundation, but his professional career soon moved toward military aviation.

Kelly joined the United States Navy, where he trained as a naval aviator and eventually became a highly experienced fighter pilot and test pilot.

NASA's biography records that he accumulated more than 8,000 hours in more than 40 different aircraft and spacecraft and completed more than 250 aircraft carrier landings.

This extensive aviation background eventually became one of the reasons he was selected for NASA's astronaut corps.

Scott Kelly as a Navy Fighter Pilot

As a naval aviator, Kelly flew high-performance military aircraft and gained experience operating in demanding environments.

He later became a test pilot, a role requiring pilots to evaluate aircraft performance, systems, and handling characteristics under carefully controlled conditions.

Test pilots must combine flying ability with engineering knowledge because they often collect and analyze technical information while operating experimental or modified aircraft.

This combination of engineering, aviation, military discipline, and technical analysis made Kelly well suited to NASA's astronaut program.

He eventually retired from the U.S. Navy as a captain in June 2012, although by that time his career had already moved from naval aviation to spaceflight.

Scott Kelly Becomes a NASA Astronaut

In April 1996, NASA selected Scott Kelly as a member of its 16th astronaut class.

He reported to NASA's Johnson Space Center in Houston in August 1996 and began the extensive training required to become a Space Shuttle and International Space Station astronaut.

His training included spacecraft systems, spacewalking procedures, robotics, survival skills, flight operations, and other technical disciplines required for human spaceflight.

After completing his initial training, Kelly worked in NASA's Astronaut Office on spacecraft systems and operations.

He also later served as NASA's Director of Operations at Star City, Russia, supporting U.S. astronaut operations and training associated with the Russian space program.

This international experience would become especially relevant later in his career because his longest space mission was a joint U.S.-Russian effort.

Scott Kelly's First Spaceflight: STS-103

Scott Kelly's first journey into space took place in December 1999 aboard Space Shuttle Discovery.

The mission was STS-103, a servicing mission to the Hubble Space Telescope.

Kelly served as the shuttle's pilot.

The mission lasted approximately eight days and focused on repairing and upgrading the Hubble Space Telescope so that it could continue conducting scientific observations of the universe.

STS-103 included three spacewalks and completed 120 orbits of Earth, traveling approximately 3.2 million miles.

For Kelly, the mission marked the beginning of a spaceflight career that would eventually include four missions and more than 500 days in orbit.

Scott Kelly and Space Shuttle Endeavour

Kelly's second spaceflight came in August 2007 aboard Space Shuttle Endeavour.

The mission, STS-118, traveled to the International Space Station.

This time, Kelly served as the mission commander.

Endeavour delivered equipment and supplies to the ISS and installed an additional truss segment, a gyroscope, and an external spare-parts platform. The mission also involved four spacewalks conducted by three crew members.

STS-118 lasted approximately 12 days, 17 hours and 55 minutes and covered about 5.3 million miles.

The mission represented a major step in Kelly's career because it gave him experience commanding a complex human spaceflight mission.

Scott Kelly's First Long-Duration ISS Mission

Kelly returned to space in October 2010, this time beginning a long-duration mission aboard the International Space Station.

He launched aboard the Soyuz TMA-M spacecraft and became a member of Expedition 25.

Later, he became commander of Expedition 26.

Kelly spent approximately 159 days aboard the ISS during this mission.

The experience prepared him for his most ambitious mission yet: NASA's One-Year Mission.

Scott Kelly's Historic One-Year Mission

The most important chapter in Scott Kelly's space career began on March 27, 2015.

Kelly and Russian cosmonaut Mikhail Kornienko launched toward the International Space Station for a mission designed to last approximately one year.

They eventually spent 340 days aboard the ISS, returning to Earth on March 2, 2016.

The mission was significantly longer than the typical six-month ISS expedition.

Its primary purpose was to help scientists understand how the human body responds to the physical and psychological demands of extended spaceflight.

This was particularly important because future missions to Mars could require astronauts to spend years away from Earth.

Why Scott Kelly Spent a Year in Space

Living in space for a year is very different from spending a few days or weeks in orbit.

Long-duration spaceflight exposes astronauts to challenges such as:

• Microgravity

• Radiation

• Changes in muscles and bones

• Altered vision

• Psychological isolation

• Changes to the immune system

• Sleep and circadian-rhythm disruption

• Limited medical support

• Long periods away from Earth

NASA therefore used Kelly's mission to conduct a large collection of scientific investigations.

Kelly and Kornienko participated in 23 investigations across seven research disciplines, providing information about the effects of long-duration spaceflight on the human body and mind.

Scott Kelly and the NASA Twins Study

One of the most remarkable aspects of Kelly's yearlong mission was that he had an identical twin brother who was also a former astronaut.

While Scott Kelly spent 340 days in space, Mark Kelly remained on Earth.

This created an extraordinary scientific opportunity.

Because identical twins share virtually the same genetic background, scientists could compare the biological changes experienced by Scott during spaceflight with measurements from Mark on Earth.

The research became known as the NASA Twins Study.

Ten research teams collaborated on the project, examining physiological, molecular, behavioral, cognitive, genetic, and microbiological changes associated with long-duration spaceflight.

It was one of the most comprehensive investigations ever conducted into the effects of spaceflight on a single human being.

What Did the Twins Study Discover?

The NASA Twins Study found that the human body is remarkably resilient during and after long-duration spaceflight, although researchers observed numerous changes at the molecular, cellular, physiological, and cognitive levels.

Researchers observed changes involving areas such as:

• Gene expression

• Immune-system activity

• Gut microbiome

• Metabolism

• Cardiovascular function

• Cognitive performance

• Telomeres

• Inflammation

Importantly, NASA clarified that Scott Kelly's DNA itself did not fundamentally change. Some changes occurred in gene expression, which describes how genes respond to environmental conditions.

The findings helped scientists understand which changes occur during spaceflight and which tend to return toward normal after an astronaut comes back to Earth.

Scott Kelly's 340 Days in Orbit

Kelly's One-Year Mission lasted 340 days, making him the first American astronaut to spend approximately a year continuously in space.

During the mission, he and his crew conducted hundreds of experiments and scientific investigations.

NASA records that Kelly completed approximately 5,440 orbits of Earth during the yearlong mission.

From the ISS, he also photographed Earth extensively.

His photographs became famous for showing the planet's landscapes, oceans, deserts, cities, mountains, clouds, and atmospheric phenomena from orbit.

These images helped communicate the beauty and interconnectedness of Earth to millions of people.

Scott Kelly's Spacewalks

During his final mission, Kelly completed three spacewalks.

The activities included station maintenance and upgrades that helped prepare the ISS for future spacecraft and improve station systems.

One spacewalk involved routing cables to prepare for new docking ports for U.S. commercial crew spacecraft.

Another involved work on the station's ammonia cooling system and helped restore the station's solar-power-generating capability.

The third spacewalk involved work on the station's Mobile Transporter system.

These tasks demonstrate that long-duration astronauts are not simply passengers or laboratory researchers. They are also responsible for maintaining and upgrading the complex spacecraft in which they live.

Scott Kelly and International Cooperation

The One-Year Mission was a major example of international cooperation in space exploration.

Kelly worked closely with Russian cosmonaut Mikhail Kornienko, and the ISS crew represented multiple countries.

During the yearlong mission, 13 astronauts and cosmonauts from seven nations lived aboard the station at different points.

This international environment demonstrated how space exploration can bring together nations with different languages, cultures, and political systems around shared scientific and technological goals.

Scott Kelly's Spaceflight Record

When Kelly completed his One-Year Mission, he had accumulated approximately 520 days in space across four missions.

NASA noted that he broke the American record for cumulative time in space during the mission.

It is important to distinguish this historical record from the current record. Kelly's achievement was extraordinary, but other astronauts later surpassed his total time in space.

His more enduring contribution is the scientific value of his long-duration mission and the Twins Study.

Scott Kelly Retires From NASA

Scott Kelly retired from NASA effective April 1, 2016, shortly after returning from his yearlong mission.

His retirement marked the end of a NASA career spanning approximately two decades.

However, his involvement in scientific research did not end when he left the astronaut corps.

Kelly continued participating in research connected to the One-Year Mission and provided medical samples and other information required for the ongoing Twins Study.

Scott Kelly as an Author and Photographer

After his astronaut career, Kelly continued sharing his experiences through books and public appearances.

His memoir Endurance: A Year in Space, A Lifetime of Discovery describes his life, military career, astronaut training, and year aboard the ISS.

He also published Infinite Wonder: An Astronaut's Photographs from a Year in Space, showcasing photographs taken during his time aboard the ISS. His official website lists these books alongside other works, including a young readers' edition of Endurance.

His photography has become an important part of his public legacy because it gives people on Earth a visual perspective of the planet from orbit.

Scott Kelly and Earth Observation

One of the most visually memorable parts of Scott Kelly's career was his photography of Earth from the International Space Station.

From approximately 400 kilometers above the planet, familiar geographic features appear in completely different ways.

Mountain ranges, coastlines, deserts, rivers, agricultural patterns, cities, ice sheets, and clouds can reveal patterns that are difficult to appreciate from the ground.

Kelly's images therefore provide more than beautiful photographs. They offer a different way of thinking about Earth's geography.

From orbit, national borders are generally invisible. Instead, the planet appears as one interconnected system of land, water, atmosphere, and life.

Scott Kelly and the Future of Mars Exploration

The One-Year Mission was designed partly as preparation for future human exploration beyond low Earth orbit.

A crewed mission to Mars would be dramatically longer than a typical ISS expedition.

NASA's research from Kelly's mission therefore focused on understanding the challenges of long-duration human spaceflight.

The Twins Study specifically described Kelly's year in space as a stepping stone toward missions such as a three-year round trip to Mars.

Research from Kelly's mission continues to contribute to NASA's broader understanding of how humans can remain healthy during extended missions.

Scott Kelly's Connection to Geography

Scott Kelly's career has a particularly strong relationship with geography because much of his public legacy involves seeing Earth from space.

Before becoming an astronaut, Kelly's work was focused on aviation and spacecraft.

Once aboard the ISS, however, he gained an entirely different relationship with the planet.

During his year in space, he completed thousands of orbits and repeatedly watched Earth pass beneath him.

He observed:

• Continents

• Oceans

• Mountain ranges

• Deserts

• Rivers

• Cities

• Polar regions

• Storm systems

• Atmospheric phenomena

His photographs helped show how Earth's physical geography appears when viewed from orbit.

Kelly's career can therefore be represented as:

Earth → Aviation → Space Shuttle → International Space Station → Global Earth Observation → Future Mars Exploration

His story demonstrates that geography is not limited to maps on a classroom wall. From space, astronauts experience geography on a planetary scale.

Explore More Geography With GeoMapGame

Scott Kelly spent hundreds of days looking down at Earth from orbit, observing the planet's continents, oceans, landscapes, cities, and geographic patterns from a completely different perspective.

If you enjoy exploring countries, capitals, continents, landmarks, maps, and geographical facts, you can discover more geography challenges on GeoMapGame.

It is a fun way to test your geographical knowledge and explore the world from a new perspective.

Scott Kelly's Major Achievements

Four Spaceflights

Scott Kelly completed four space missions between 1999 and 2016, including Space Shuttle missions and long-duration ISS expeditions.

340-Day One-Year Mission

He spent 340 consecutive days aboard the ISS during NASA's One-Year Mission with Mikhail Kornienko.

About 520 Days in Space

By the end of his career, Kelly had accumulated approximately 520 days in space, setting an American cumulative spaceflight record at the time.

ISS Commander

Kelly commanded multiple International Space Station expeditions, including Expeditions 26, 45 and 46.

NASA Twins Study

His year in space enabled NASA's landmark Twins Study, comparing Scott's biological changes in orbit with those of his identical twin brother Mark on Earth.

Hubble Space Telescope Mission

His first spaceflight, STS-103, involved servicing and upgrading the Hubble Space Telescope.

Extensive Aviation Experience

Kelly accumulated more than 8,000 flight hours across more than 40 aircraft and spacecraft and completed more than 250 carrier landings.

Scott Kelly Career Timeline

Year	Milestone
1964	Born in Orange, New Jersey
1980s	Studied engineering and entered naval aviation
1996	Selected by NASA as an astronaut
1999	Flew first mission, STS-103, to service Hubble
2007	Commanded Space Shuttle Endeavour on STS-118
2010	Began long-duration ISS mission
2011	Commanded Expedition 26
2012	Retired from the U.S. Navy
2015	Began NASA's One-Year Mission aboard the ISS
2016	Returned after 340 days in space
2016	Retired from NASA
2019	NASA published major integrated findings from the Twins Study
After NASA	Continued writing, public speaking, photography and science outreach

Frequently Asked Questions About Scott Kelly

Who is Scott Kelly?

Scott Kelly is a retired NASA astronaut, engineer, former U.S. Navy captain, naval aviator, and test pilot who completed four spaceflights and spent approximately 520 days in space.

What is Scott Kelly famous for?

Scott Kelly is best known for spending 340 consecutive days aboard the International Space Station during NASA's One-Year Mission and participating in the landmark Twins Study with his identical twin brother, Mark Kelly.

How long did Scott Kelly stay in space?

Scott Kelly spent 340 consecutive days aboard the ISS during his One-Year Mission. Across all four spaceflights, he accumulated approximately 520 days in space.

How many times did Scott Kelly go to space?

Scott Kelly flew to space four times: STS-103 in 1999, STS-118 in 2007, an ISS expedition beginning in 2010, and the One-Year Mission beginning in 2015.

What was the NASA Twins Study?

The NASA Twins Study compared Scott Kelly, who spent nearly a year in space, with his identical twin brother Mark Kelly, who remained on Earth. Scientists used the unusual genetic similarity between the brothers to study how long-duration spaceflight affects the human body.

Is Scott Kelly still a NASA astronaut?

No. Scott Kelly retired from NASA in April 2016 after completing his One-Year Mission.

How many spacewalks did Scott Kelly complete?

Kelly completed three spacewalks during his 340-day One-Year Mission.

Who is Scott Kelly's twin brother?

Scott Kelly's identical twin brother is Mark Kelly, who is also a former NASA astronaut. Mark remained on Earth during Scott's 340-day mission and served as the comparison subject for the NASA Twins Study.

Did Scott Kelly help prepare NASA for Mars missions?

Yes. NASA designed the One-Year Mission and associated research to better understand the effects of long-duration spaceflight and to help prepare for future missions beyond low Earth orbit, including potential human missions to Mars.

Conclusion

Scott Kelly's biography is a story of aviation, engineering, space exploration, scientific research, and endurance.

His career began with engineering and naval aviation before taking him into NASA's astronaut corps. Across four spaceflights, he flew to the Hubble Space Telescope, commanded a Space Shuttle mission, led International Space Station expeditions, and ultimately spent 340 consecutive days in orbit.

His final mission became particularly significant because it transformed his own body into an important subject of scientific research. By comparing Scott with his identical twin brother Mark, NASA scientists gained a rare opportunity to study the effects of long-duration spaceflight on a human being.

Scott Kelly's story is therefore about more than a record number of days in space. His mission helped answer fundamental questions about how humans adapt to living away from Earth and provided knowledge that could support future exploration of the Moon, Mars, and beyond.

From flying Navy aircraft to commanding spacecraft and watching Earth from orbit, Scott Kelly's career represents one of the most important chapters in the history of long-duration human spaceflight.