Final spacewalk underway before return to Earth

The fourth and final spacewalk of the shuttle Atlantis' mission to the International Space Station is underway.

The two astronauts plan to install a camera, a debris shield and a computer cable between the American and Russian sides of the space station during the six-hour operation.

The space shuttle Atlantis has been cleared for its return to Earth next week. Its mission had been extended because of a computer failure and a tear in the thermal shield.