The view from the International Space Station is about to get a lot better, as the largest window ever built for use in space has been completed.

The construction of the window was originally funded by NASA and Boeing. However, when NASA's budgets were tightened in 1998, the project ran out of money. The European Space Agency (ESA) agreed to complete the construction as part of a "barter agreement" with NASA.

The circular window, measuring 80 cm across, sits in the centre of an observation dome called Cupola, flanked by six, smaller, trapezoid viewpanes. Each pane consist of four layers of silica, fused together to produce a 10cm-thick, transparent panel, the BBC reports.

The external pane needs to withstand the kind of battering any object in orbit can expect: tiny objects at orbital speed are more energetic than a bullet fired from a rifle. The inner layer need only withstand the constant battering it will get from tumbling astronauts - small fry, in comparison. The two central layers in the silica sandwich deal with the significant pressure differences between the pressurised space station and the vacuum of space.

The window gives astronauts living on the ISS a better view of what they are doing when operating the station's external robotic arm. The dome has a diameter of about 2 metres and is about 1.5 metres tall, providing a 'shirtsleeves' work environment for two people.

As a side benefit, the unparalleled view of the Earth will provide long-stay astronauts with a psychological boost, according to Doriana Buffa, Cupola project manager at Alenia Spazio, the company responsible for the final construction.

Maurizio Tucci, the company's CEO, said the knowledge gained from the project will be invaluable in expeditions calling for long stays in space, such as getting humans to back to the Moon, and even to Mars.

The next step is transportation to the Kennedy Space centre for full approval in November this year. If approved, the window will be fitted to Node-3 of the ISS as part of the January 2009 mission. ®

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