John Glenn was the first American to orbit Earth, circling our planet three times in the space capsule he named Friendship 7, on 20 February 1962. The early US space programme was not primarily a scientific endeavour, but a military effort to beat the Soviets to the Moon. We early US astronauts who flew in the Mercury, Gemini and Apollo missions were pilots — military men — but we became celebrities. Glenn carried the international media attention with such dignity that he became the iconic All-American Boy. Committed to public service, he later served four terms in the US Senate. He died on 8 December 2016.

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Born in Cambridge, Ohio, on 18 July 1921, John Herschel Glenn Jr studied engineering at Muskingum College in New Concord, Ohio. After the United States entered the Second World War, he elected not to complete his senior year. Instead, Glenn, already a licensed aviator, left college to become a fighter pilot, earning a commission in the Marine Corps. By the end of his Second World War and Korean War service, he had flown 149 combat missions — he shot down three Soviet-built fighters, and twice landed with more than 250 holes in his own aeroplane.

Captivated by space flight, Glenn volunteered to serve in simulators to test the disorientation and extreme G forces astronauts would encounter. In 1958, when the newly formed NASA recruited its first class of astronauts, Glenn barely met the criteria — he was near the upper age limit, and he lacked a bachelor's degree in science. Nevertheless, he earned a position as one of the Mercury Seven. Like most fighter pilots, he did not doubt his capabilities, did not shrink from taking chances and would not give up.

Glenn's Friendship 7 flight was anything but a solo effort. He relied on some 40,000 collaborators worldwide — from private contractors making components to personnel at remote-tracking stations and sailors aboard ships ready to recover him at splashdown. It was an immense physical, technical, military and scientific achievement. But Glenn alone carried the mission's risk: it was he, a 40-year-old married father of two, who put his life on the line.

For NASA and the United States, Glenn's achievement was dramatic. Millions of people around the world followed the mission live, well aware that things could go wrong. Because Soviet space missions were shrouded in secrecy, with their results revealed only after successful conclusions, Glenn's mission signalled the achievements of free enterprise. Today, it continues to signal the importance of public funding for science, engineering and exploration.

But his mission's real achievement has been philosophical: one of understanding the majesty of our planet. Glenn realized this even before his launch, and fought for special permission to carry a camera that he had bought. On his very first orbit John saw Earth as a magnificent place, and although he was a disciplined test pilot with a rigid flight plan, he elected to deviate and photograph Earth, exclaiming for all the world to hear, “Oh that view is tremendous ... Beautiful sight.”

Likewise, when I first saw our blue planet coming up from the rugged lunar horizon, I deviated from the Apollo 8 flight plan, grabbed a camera and shot a photograph with a 270-mm lens I had to fight to get aboard, capturing the image now known as 'Earthrise'. Our shared elation at what we saw served not as just another battle in the cold war, but as a beginning for a more global awareness of a borderless planet, finite and shared.

Colonel Glenn left NASA in 1964 — President John F. Kennedy had found him too valuable to risk his life again. He worked in private industry before running for the US Senate as a Democratic candidate, only to face narrow defeat. Never one to give up, Glenn ran again and carried all of Ohio's 88 counties in 1974. He served in the Senate until he resigned in 1999, championing science and science education, along with nuclear non-proliferation.

In the 1970s, when I was a member of the US Atomic Energy Commission, I testified several times before Senator Glenn's subcommittee on non-proliferation. Having viewed our beautiful planet from space, we were both motivated to devise practical ways to lessen the chances of spoiling it with mushroom clouds.

Senator Glenn also encouraged study of our ageing population. In 1998 he was selected, at the age of 77, to fly aboard the space shuttle Discovery on a 9-day mission during which biometric measurements would lend insight into how an ageing human body responded to space flight.

Glenn's personal life was itself notable. In 1943, Glenn married Anna 'Annie' Margaret Castor, with whom he had grown up — they had literally played in the same crib together. Glenn remained devoted to his wife to the end. His life, from the moment he became a Mercury astronaut, was lived significantly in the public eye. Glenn's space flight marked the emergence of a new kind of celebrity, but he laboured to limit its intrusion into his private life, shielding his family from the spotlight.

Glenn's iconic flight, and the broader Mercury, Gemini and Apollo programmes with their eventual lunar landings, did accomplish their cold-war missions. Of more lasting significance, they saw lunar explorers who went to study the Moon discover Earth instead, something that led us both to become lifelong supporters of environmental and science education.

Godspeed, John Glenn.