Windows for manned spacecraft

The windows of the Cupola aboard ISS. The 12th European Conference on Spacecraft Structures, Materials and Environmental Testing, hosted at ESA’s technical centre at Noordwijk, the Netherlands, on 20–23 March 2012 included a discussion of designing and testing windows for manned space vehicles.
Richard Lamoure of space engineering firm Magna Parva recounted how early US astronauts had to insist on having windows in their space capsules. Nowadays they are regarded as essential for docking and manoeuvring, spacewalk support, scientific monitoring and crew morale.
“People just like to look outside, even if what is outside is certain death,” said Mr. Lamoure, whose company is working on an ESA contract to develop a window-verification methodology for future spacecraft.
Fundamentally, glass is brittle. Any initial crack could over time lead to larger fractures – and the larger the pane the more likely such flaws are likely to be present. So the study is developing a rigorous test system, including numerical modelling, bending tests where pressure is applied and acceptance tests where the candidate pane is scrutinised for cracks.