Astronauts attach ammonia coolant to space station

Two spacewalking astronauts have completed their mission to attach a canister of ammonia coolant to the International Space Station.

Daniel Barry and Patrick Forrester also hung up trays holding 750 science samples.

It is the first experiment mounted to the outside of space station Alpha, which marked its 1,000th day in orbit on Thursday.

The astronauts hitched a ride to the space station on space shuttle Discovery's robot arm.

The two shuttle astronauts clung to the ammonia container, measuring 1.2 metres by 2.4 metres, as shuttle commander Scott Horowitz. hoisted it from Discovery's cargo bay.

Because the arm could not reach all the way, Barry and Forrester had to line up the ammonia container themselves.

It was slow, methodical work made more difficult by the fact that they had to move the device further than planned.

The ammonia will serve as spare coolant for the space station's electronics in case of a leak in the primary system. It should have been delivered last spring, but needed repairs.

Barry and Forrester also attached two briefcase-like boxes to the space station and opened them to expose small samples of coatings, polymers, switches, mirrors, seeds, spores and bacteria. The trays resembled a painter's palette.

NASA wants to see how the materials fare in the harsh environment of space so engineers can build stronger satellites and devise better radiation shielding for astronauts and cosmonauts bound one day for Mars.