Two spacewalking astronauts are performing several tasks outside the International Space Station (ISS) on Tuesday. An American and an Italian astronaut ventured outside the orbiting laboratory early Tuesday. It is the first spacewalk for Italy, a major contributor to the ISS. The other space-station crew members - one American and three Russians - assisted the spacewalkers from inside. The first task, which took longer than expected, was the installation of a new space-to-ground radio transmitter after the old one failed in December. The astronauts also collected science experiments for return to Earth later this year aboard a commercial SpaceX capsule. Other tasks to be performed include removing a failed camera and relocating radiator grapple bars. Some of the work was targeted as potential future breakdowns, making it easier to exchange bad parts when the time comes. The astronauts also have some cable work to perform in preparation for a new Russian laboratory due to arrive in December, and they were asked to take pictures of the Alpha Magnetic Spectrometer, a $2 billion cosmic-ray detector launched on the U.S. space agency\'s next-to-last shuttle mission in 2011. A second spacewalk, scheduled for next Tuesday, will conclude the tasks, National Aeronautics and Space Administration (NASA) officials said.