"Our focus is completing this mission, doing it successfully. We understand this is a human interest story, but you know our primary focus is doing the job and getting home safely."

The February mission marks the end of NASA's Space Shuttle program.

Endeavor Commander Mark Kelly [bottom center] with crewmates, will make the 36th and perhaps final mission to the International Space Station.

While some critics warn that its shutdown could pose access and supply problems for the International Space Station, Endeavor commander Mark Kelly says it's time for the Space Agency to retire the shuttle and chart new directions.

"The shuttle was designed to build a space station and after STS-134, the International Space station will be complete. It has really done its job," he says. "And in order for us to build a new class of rockets and a new spacecraft and to do other things, we are going to have to retire the space shuttle."

Scott and Mark Kelly say their work in space has been a privilege and both feel it's been an honor to serve their country through the space program. They say their numerous trips to earth orbit have given them a new perspective on the planet.

Scott says, when he looks down on earth from space, political borders disappear. "It makes an impression on you that we are all part of planet earth."

Mark agrees. "The atmosphere is a little sliver that is pretty thin and fragile. You think about what we all need to do to protect it."