Two US astronauts left the International Space Station for a spacewalk to prepare the last piece of Japan's Kibo laboratory for installation on the orbital complex.
Lead spacewalker David Wolf and astronaut Timothy Kopra slipped out of the station's airlock to begin the first of five spacewalks planned during shuttle Endeavour's stay at the station.
The shuttle arrived yesterday for an 11-day mission.
The ISS and the Endeavour will be visible as a brilliant star-like object in the skies over Ireland at approximately 11.21pm tonight.
Chairman of Astronomy Ireland David Moore said there are a record 13 astronauts on board the ISS-Shuttle complex, which will be visible over Ireland every night until 23 July.
The main goal of the spacewalk is to prepare a Japanese-built platform to be attached to the front of the station's $2.4 billion (€1.69bn) Kibo laboratory.
The platform is designed to hold experiments that need to be exposed to the open environment of space.
The spacewalkers also have some station maintenance chores on their to-do list, including working on an equipment cart and preparing a docking port for Japan's new cargo ship, which is scheduled to make its debut flight later this year.
NASA also completed its initial analysis of Endeavour's heat shield on Saturday, and determined that no additional inspections would be needed by the shuttle crew.
