American space legend John Glenn dead at 95

The US space agency NASA was among the first to pay tribute to the legendary astronaut who went on to serve in the Senate for more than two decades, calling him "a true American hero."

"Godspeed, John Glenn. Ad astra," NASA tweeted.

Glenn died at the James Cancer Hospital in Columbus, Ohio, according to Hank Wilson, a spokesman for the John Glenn College of Public Affairs. The cause of death was not immediately given.

"With John's passing, our nation has lost an icon and Michelle and I have lost a friend," President Barack Obama said in a statement.

"When John Glenn blasted off from Cape Canaveral atop an Atlas rocket in 1962, he lifted the hopes of a nation."

The onetime astronaut and veteran of two wars had been in declining health, undergoing heart-valve replacement surgery in 2014 and reportedly suffering a stroke, and was admitted to the cancer ward in Columbus more than a week ago.

"Though he soared deep into space and to the heights of Capitol Hill, his heart never strayed from his steadfast Ohio roots," said John Kasich, the governor of Glenn's midwestern home state, in one of the stream of tributes flooding in for the late legend.

"Aren't many Heroes left," tweeted the astrophysicist Neil deGrasse Tyson. "WWII & Korean War Fighter Pilot. Marine Colonel. NASA Astronaut. Senator. Married 73 yrs."

On February 20, 1962, Glenn became the first US astronaut to orbit the Earth, in a flight lasting just under five hours and circling the Earth three times, as part of NASA's Mercury project.

Thirty-six years later, on October 29, 1998, he made history again when he returned to space at the age of 77 -- becoming the oldest astronaut in space.

It was another shining moment in a career of trailblazing successes spanning decades.

Born July 18, 1921 in Cambridge, Ohio, Glenn joined the US Marine Corps in 1943, becoming a fighter pilot.

He served in the Pacific during World War II, and later in the Korean War, flying a total of 149 combat missions. According to his official biography, Glenn downed three fighter jets over the Yalu River in the final nine days of fighting in Korea.

In 1957 he made the first nonstop supersonic flight from Los Angeles to New York and became an astronaut two years later.

After his 23-year career in the US military and space program, which ended in 1965, Glenn entered the Senate as a Democrat. He made two unsuccessful tries for the presidential nomination, in 1984 and 1988.

While in the Senate Glenn was politically progressive, keeping a relatively low profile in Congress. He specialized in the fight against nuclear weapons proliferation and the disposal of nuclear waste.

He also flew his own aircraft, a Beechcraft Baron, between the capital and his home state of Ohio, boasting about his record time of one hour, 36 minutes from Washington to Dayton.

Glenn also kept fit, making his return to space possible.

He regularly passed NASA physicals and pressed the space agency to consider the possibility of sending an older person -- such as himself -- into space for research, particularly on the effects of weightlessness on the elderly.

In November 2011, then 90 years old, Glenn was awarded the Congressional Gold Medal, with three others, the first time the prize was awarded to astronauts.

"We came in peace for all mankind," he said after receiving the award, before repeating the words he spoke half a century earlier, addressing lawmakers upon returning from his orbital flight.

"As our knowledge of the universe in which we live increases, may God grant us the wisdom and guidance to use it wisely."

In 2012, Obama awarded Glenn the Presidential Medal of Freedom, the country's highest civilian honor.

"The last of America's first astronauts has left us, but propelled by their example we know that our future here on Earth compels us to keep reaching for the heavens," the president said in his tribute to the late legend.

"John always had the right stuff, inspiring generations of scientists, engineers and astronauts who will take us to Mars and beyond -- not just to visit, but to stay," said Obama.