Astronauts embark on 1st spacewalk of mission

CAPE CANAVERAL -- A couple of astronauts have stepped out on a spacewalk at the international space station.

The first spacewalk of the mission got underway Tuesday evening, shortly after the space station got a new $5 million treadmill. The treadmill is named after TV comedian Stephen Colbert, who was out of the country Tuesday. But he said through his New York publicist that he was proud his treadmill would be used "to help trim down those famously fat astronauts."

Spacewalkers Nicole Stott and Danny Olivas will remove an old ammonia tank from the space station. A new, fully loaded tank will be installed during another spacewalk Thursday as part of the cooling system. In all, three spacewalks are planned during shuttle Discovery's visit.