NASA sent a 77-year-old payload specialist back into space in 1998, 36 years after he became the first American to orbit Earth - not just to make history again, but to study how an older human body responds to microgravity, becoming the oldest person ever to fly in space

Thirty-six years after John Glenn became the first American to orbit the Earth and an instant hero of the Space Race, NASA sent him back into space. But this time, Glenn was no longer the young Mercury astronaut who had climbed into the tiny Friendship 7 capsule in 1962. He was 77 years old.

On October 29, 1998, Glenn climbed aboard the space shuttle Discovery as a payload specialist for mission STS-95, beginning a journey that would make him, at the time, the oldest person ever to travel into space. Yet his extraordinary return was not simply about breaking an age record. NASA had another reason for sending the pioneering astronaut back into orbit: his age offered scientists an unusual opportunity to investigate the connections between spaceflight and the human aging process.

For Glenn, it was a remarkable return to the environment that had transformed him into one of America's most recognizable figures.

From historic orbit to an unlikely return

On February 20, 1962, Glenn flew aboard Friendship 7 and became the first American to orbit the Earth. The mission demonstrated that the United States was a serious competitor in the Space Race against the Soviet Union and turned Glenn into an instant national hero.

After leaving NASA in 1964 and retiring from the Marine Corps, Glenn entered public life. He later served four terms as a US senator from Ohio, where the challenges facing an aging population became one of the areas connected to his work.

Then, in 1998, NASA gave the space pioneer an opportunity few could have imagined. Glenn would return to orbit.

His second journey into space came aboard Discovery's STS-95 mission, launched from Launch Pad 39B at Kennedy Space Center on October 29, 1998. The mission would last 9 days, 19 hours, 54 minutes and 2 seconds, travelling about 3.6 million miles and completing 134 revolutions around Earth before landing back at Kennedy Space Center on November 7.

Glenn, the Payload Specialist was not alone aboard Discovery. He flew as one of seven crew members on STS-95, alongside commander Steven Lindsey, pilot Stephen Robinson, mission specialists Pedro Duque, Scott Parazynski and Stephen Frick, and payload specialist Chiaki Mukai.

Why NASA sent a 77-year-old astronaut into space

Glenn's age was not merely a historical curiosity. One of the major scientific interests behind his flight involved the similarities between some changes experienced by the human body during spaceflight and the natural changes associated with aging.

NASA scientists recognize parallels between the effects of microgravity and aspects of the aging process. During the mission, Glenn participated in investigations examining how his body responded to the unusual environment of space. The research focused on areas including balance and perception, immune-system response, bone and muscle density, metabolism, blood flow and sleep.

Glenn was not the only crew member involved in medical research. NASA also conducted tests involving Mission Specialist Pedro Duque as part of its efforts to understand how the absence of gravity affects the human body.

The mission therefore gave scientists an unusual chance to study an older astronaut in microgravity while exploring questions connected to both space medicine and aging on Earth.

More than 80 experiments in nine days

STS-95 was far more than John Glenn's personal return to orbit. A slate of more than 80 experiments filled the nearly nine-day mission. The crew conducted medical and materials research while also carrying out several other major scientific operations.

Discovery deployed the Petite Amateur Naval Satellite, or PANSAT, to test technologies for capturing and transmitting weak or interference-filled radio signals.

The crew also released the Spartan free-flying satellite, which studied the Sun and the solar wind. The research aimed to help scientists better understand phenomena capable of causing widespread disruptions to communications and power supplies on Earth.

The mission also carried the Hubble Space Telescope Orbital Systems Test, providing an on-orbit testing environment for hardware intended for the telescope's third servicing mission. But amid all those experiments, Glenn remained the mission's most symbolic passenger.

The man who came back

The contrast between Glenn's two spaceflights was extraordinary. In 1962, he had entered orbit as one of NASA's original Mercury astronauts, helping establish America's place in human space exploration.

In 1998, he returned 36 years, eight months and nine days later, not to repeat his earlier achievement, but to contribute to scientific research at an age when most people would never imagine beginning such a physically demanding journey.

His flight aboard Discovery made him the oldest human to venture into space at the time, while turning his own body into part of NASA's investigation into aging and spaceflight.

Glenn's story had therefore come full circle. The man whose 1962 flight showed that America could compete in the Space Race returned decades later to help NASA ask a different questionm, not simply how far humans could travel, but how the human body changes when it leaves Earth.

John Glenn died on December 8, 2016, at the age of 95. But his final journey into space remains one of NASA's most unusual chapters: a 77-year-old pioneer returning to orbit 36 years after making history, becoming the oldest person to fly in space and helping scientists explore what spaceflight might reveal about the process of growing old.