Astronauts take 2nd spacewalk to replace tank

CAPE CANAVERAL, Fla. (AP) - Astronauts are back outside the International Space Station, making their second spacewalk in three days to replace an old storage tank.

Rick Mastracchio and Clayton Anderson floated out early Sunday.

Mastracchio and Anderson will be dealing with ammonia tanks, part of the space station's cooling system. They will remove a nearly empty tank that's been up there for eight years. Then they will plug in the new one that was delivered by space shuttle Discovery last week.

It's the 40th anniversary of the launch of Apollo 13, which resulted in one of the world's most dramatic rescues ever. The accident occurred two days after liftoff when an oxygen tank ruptured, while the three-man crew was en route to the moon.