Nasa is marking an historic milestone on Wednesday (3 June): 50 years since astronaut Edward Higgins White became the first American to step into space.

That first spacewalk for the US happened on 3 June 1965, during the second manned spaceflight in Nasa's Project Gemini, which had astronauts James McDivitt and Ed White circle Earth as many as 66 times over the period of a four-day mission.

The pictures and video of White on that first US spacewalk, floating above Earth in a white spacesuit with tethers tumbling behind him, are still widely published today.

"It's just an amazing adventure out there in that one-person space suit," said Nasa astronaut Michael Foreman who was on hand at the Nasa's space centre in Houston to commemorate the historic occasion. "To look down between your feet, and see the earth passing 250 miles below you, it's just breathtaking."

A naval aviator by training, Foreman was selected by Nasa in June of 1998, to undergo the extensive, arduous training by Nasa which he says prepared him for the unknown.

"You're not 100% sure how you're going to feel until you experience that for the very first time," said Foreman. "Fortunately for me, I felt very comfortable out there, and it was just like muscle memory took over when I went out that hatch for the very first time, because I was just so used to doing the same thing here in the training we had in the pool."

Foreman, who has logged more than 637 hours in space, including 32 hours and 19 minutes in five spacewalks, says Nasa has come a long way since that first spacewalk by White, half a century ago.

"The suits have advanced. The tools that we use to work on the International Space Station have advanced. The procedures and techniques we use when we're doing spacewalks have certainly advanced," said Foreman.

"And we have a ways to go, I think, because we're looking forward to going to Mars in a couple more decades," said Foreman.

Foreman doesn't plan to go up again, saying it's time for his generation to step aside and let the next generation take over the mission to Mars.

The dangers of space exploration is not lost on astronauts like Foreman, since the smallest factor, like a minor tear in the space suit, could be life threatening. In-flight accidents have killed 18 astronauts, in four separate incidents. As to why he would risk his life to explore the unknown?

"We do it is because we believe in the exploration of space," said Foreman. "The tasks that we're going outside on these spacewalks to do, are important for those goals that we have to explore space and to learn things about living here on earth."

White is the second man to walk in space. Russian cosmonaut Alexey Arkhipovich Leonov is the first human to braved uncharted territory when he exited the capsule during the Voskhod 2 mission, on 18 March 1965, for the first ever spacewalk. It lasted 12 minutes.