U.S. Discovery space shuttle astronauts...

NASA said on its website the two spacewalkers were due to replace an Ammonia Tank Assembly on the station"s starboard truss, a job they would continue during the third spacewalk on Tuesday.

The ammonia is used for the cooling system at the International Space Station (ISS).

On April 7, Shuttle Discovery successfully docked with the ISS manually after a malfunction on board the shuttle. Discovery blasted off on schedule at 6:21 a.m. local time (14:21 GMT) on Monday from the Kennedy Space Center in Florida on one of NASA"s final stockpiling missions to the ISS.

This is Discovery"s 33rd mission to the ISS, and the 131st mission of the Space Shuttle program.

The current mission will last 13 days and astronauts will perform three space walks, each of which is planned to last around six and a half hours.

MOSCOW, April 11 (RIA Novosti)