Engineering of windows for the International Space Station

100% of the ISS windows are manufactured from glass. As a structural material, glass is a poor choice for use in pressure vessels when failure will result in the loss of life. Structural use of glass has several difficulties. First, glass is a brittle material and fails without indication of imminent overload. Additionally, minor flaws in the surface of glass can have significant impacts on the structural integrity (ultimate strength) of material. Finally, glass is susceptible static fatigue. This material property causes the loss of ultimate strength in the material over time when the glass is under load. The windows on the ISS are exposed to a hostile environment that includes bombardment from tiny micrometeoroids that damage the material surface. Additionally, since the material is employed as part of the pressure shell, it will be constantly loaded with one atmosphere of pressure for the 15 year life. With each of the unique material problems associated with glass, how does NASA ensure the structural integrity of the ISS windows? This paper describes how NASA technically mitigates the risks associated with engineering using this difficult material.