The U.S. space agency is celebrating the 50th anniversary of the first trip of an American into Earth orbit.

John Glenn went around the planet three times in just under five hours on February 20, 1962, in a mission designed to see how man would react to the space environment.

Speaking at a NASA event last week, the 90-year-old Glenn said his experience aboard the spacecraft is hard to describe.

“You know, the things that remain very, very personal that you can't really convey are the feelings of things and the actual feel of this and that and something and just the view (of the Earth) that was different from what people had ever been able to see before and things like that.”

But he was not the first person to orbit the planet. Nearly a year before Glenn's flight, Soviet Air Force pilot Yuri Gagarin made a single pass around Earth.

Glenn, who also served four terms as the U.S. Senator from Ohio, returned to orbit aboard a shuttle mission in 1998, becoming at age 77 the oldest person to fly in space.

The former astronaut is scheduled to take part in a two-day forum beginning Monday to discuss the future of the U.S. space agency. He has criticized the decision to end the U.S. space shuttle program, which carried out its final flights last year.

American astronauts now rely on Russia to fly them into space while the United States helps fund the development of private sector spacecraft. President Obama's proposed budget for next year would double the amount of money allocated to the development program to $830 million.