Two astronauts are on the first spacewalk for the crew of the shuttle Discovery.
Scott Parazynski and Douglas Wheelock got started about 30 minutes ahead of schedule today to help install a new live-in compartment at the international space station.
They'll help astronauts inside the station operate a robotic arm that will transfer the compartment from the shuttle to the orbiting space lab.
The compartment is about the size of a school bus and weighs nearly 16 tons. It will be used as a docking port for laboratories that will arrive on the next three shuttle flights.
Parazynski and Wheelock are also to remove a broken antenna from the station and pack it on the Discovery so it can go back to Earth.
Parazynski is slated to participate in four of the five spacewalks. This is Wheelock's first trip to space.