Two astronauts are taking a few small steps on the first spacewalk of a mission at the International Space Station today.

Stephen Bowen and Alvin Drew floated outside the spacestation this morning. Bowen, who has done many spacewalks, was a last minute addition to this mission of the shuttle Discovery. He is replacing an astronaut who hurt himself in a bicycle crash last month.

Drew, on the other hand, is taking his first steps on the station today. He becomes the world’s 200th spacewalker.

During today’s walk, Drew and Bowen will install an extension cable and move a broken ammonia pump into storage. The two will also expose a canister to the contents of space that will later be on display in Japan. This mission of Discovery will be the last for the shuttle.