Manufacturing & Prototyping

Stresses caused by differential gas pressures are reduced.

A technique for reducing in-flight loss of closed-cell foam insulation has been devised. In the original application, foam is used for thermal insulation on the external tank of the space shuttle. As the space shuttle ascends, aerodynamic effects cause an increase in surface temperature of the foam. This heating increases the internal cell gas pressure and reduces cell wall strength. The difference between the increasing pressure of the gases trapped in the foam cells and the decreasing pressure of the ambient air contribute to stresses that can break off pieces of foam during flight. Perforating the foam with small holes makes it possible for some trapped gases to escape, reducing the stresses sufficiently to keep the foam intact during ascent. This technique reduced in-flight foam loss by more than 95 percent. The vent holes could offer similar benefits in other applications where materials are subjected to thermal and pressure gradients.