Two astronauts glided on the outer surface of the International Space Station in the early hours on Friday so as to commence the complicated job of replacing a big, old ammonia container on the orbiting laboratory's hull.

Discovery shuttle astronauts, Rick Mastracchio and Clayton Anderson had to make use of a meddle piece to drag the new ammonia container off its link in Discovery's payload inlet after it got jammed. But subsequently, its move to a momentary storage spot on the station went on efficiently.

The spacewalkers had to spend 6 1/2 hours functioning on the outer surface of the station to separate an unfilled ammonia container on the station and set up its replacement for fitting a new tank, later on a spacewalk. It was the primary of three spacewalks that had been planned for their operation.

The 1,700-pound ammonia containers are huge boxy pieces, which are filled with toxic coolant for the space station's thermal power system.

The old container, which the spacewalkers replaced, was vacant and would be brought back to Earth on Discovery for its renovation and refilling procedure.