By Irene Klotz
Cape Canaveral, Florida
More than 450 men and women from 34 countries have followed the world's first artificial satellite into orbit.
Astronauts say that a trip to space can completely change your outlook
They share the unique experience of living without gravity for a period of time and seeing Earth from the vantage point of space - a sight that inevitably provokes awe, humility and in many cases a heightened awareness that the planet needs to be cared for.
"The common thing that stands out is that astronauts are very dedicated," said Nasa astronaut Andy Thomas, who has made four spaceflights, including a long-duration mission on the Russian space station Mir.
"They are very focused people and they're very motivated, driven to pursue this career path," he said.
On the go
Most of the time, being an astronaut is a lot like any other engineering job. "You're in an office and attending meetings," Dr Thomas said.
Flights are few and far between, but once an astronaut is assigned to a crew, training begins in earnest. Still, little can prepare an astronaut for the pace of life on the shuttle.
"It's just go, go, go the whole time," he explains. "Normally you're supposed to have two hours after you get up to take care of everything, but usually you start work within an hour or so because there is just so much to be done.
"Because you're in orbit and you don't have a daily sunrise and sunset cycle, you tend not to be aware of time."
"I've found many times on shuttle flights that you'd be working and working and someone will say, 'aren't you going to eat dinner?' and you say, 'well I will when we get to it,' and they say, "well dinner was two hours ago'. You've missed it just because you've got so much to do.
"You come back and you think, 'My God, what was that?' because you're just exhausted and wiped out," Dr Thomas said.
He prefers the longer-duration flights typically assigned to space station crewmembers who live for six months in orbit.
"You really get to savour the serenity of the experience and all the little nuances that go with being in zero gravity," Dr Thomas said.
Despite being away from family and friends, Andy Thomas said he never felt a sense of isolation in orbit.
"You are able to look out the window and see the Earth below you and see familiar sights on a very frequent basis. It gives you a warm, fuzzy feeling," he explained.
"I think it would be different for people going on interplanetary journeys; I think they would feel a great sense of isolation."
No matter how long the mission lasts, when astronauts return to Earth it is difficult to recreate the psychological mindset of being in space.
"It's hard to go and capture the essence of what it's like up there," said Michael Lopez-Alegria, another four-time flier who served as commander of the International Space Station between September 2006 and April 2007.
"It's such a different place, it's such a parallel existence," Mr Lopez-Alegria said. "It's hard to go back and forth. I wish I could have bottled that [experience in space] and open it up and take a whiff every once in a while. The whole long experience is just one big smile for me."
Newly returned space station crewmember Sunita Williams said she came back to Earth more tolerant and with a greater consciousness about humanity's place in the Solar System.
Sunita Williams said that returning to Earth was difficult
"You have a different perspective in space," Ms Williams explained. "In today's time when we're so Earth-centric, or human-centric, we think all about us being here on the surface of the planet. What that means to us [astronauts] is that we can look at the Earth from this vast viewpoint."
Being on the space station was hard work, she added, but then you would float by a window and peek out at the planet. Remembering that is difficult after returning to Earth.
"I have things I have to do. I have a Blackberry. I have a cell phone. I have to make all these business calls and that kind of stuff and you forget that we are a planet and it's moving and it's changing and we have to take care of it," Ms Williams said.
The astronaut's priorities have changed too since her return, leaving her with little patience for television and other activities that "would just have time go away".
Ms Williams finds herself with a greater appreciation for looking at plants, walking in a forest or along a beach and "just thinking about interactions on the planet".
"I know that sounds goofy," she said, "but it's true."
"I wish everybody could go up to space just for an hour or an orbit, just to look at the planet and see all the great things about it," she added. "That would reap a lot of benefits in just having people act nicer to each other."