Aerogels in Aerospace

Catherine Chan
27 November 2012

Above: Though it has a ghostly appearance like an hologram, this aerogel is very solid. It feels like hard styrofoam to the touch (NASA)

Did you know? A silica-based aerogel is about 1,000 times less dense than glass (also made of silica), because almost the entire volume of the aerogel is empty space (it more than 95% air)!What is made almost entirely of holes yet is strong enough to support something many times its own weight? An aerogel! This article looks at how the unique thermal and mechanical properties of aerogels make them key materials for aerospace construction.

Aerogels were first developed by Samuel Kistler in the early 1930s. They were used for insulating and for repelling water, but the high cost of manufacturing limited their commercial potential. The first use of aerogels in space exploration was in 1996, when they were used in the Mars rover Sojourner, which was delivered to the Red Planet by the Pathfinder spacecraft. Since then, NASA has used aerogels in several other missions.

Aerogels are solid but porous materials like foams or sponges, only much lighter. They are made by replacing the liquid in a gel with air, creating a porous material with a very low density. Gels are semi-solid mixtures that contain a solid phase dispersed in a liquid medium, like fruit jellies. Aerogels are among the lightest materials ever created because of their high porosity.

Did you know? A nanometre is a billionth of a meter. That's about a million times smaller than the average freckle. Aerogels are excellent thermal insulators both because they have extremely small (nanometre-sized) pores that almost completely block air flow and because they are poor heat conductors (due to the presence of silica and air). They were used as insulation on Sojourner and, later, to regulate the temperature of electronics aboard the Mars rovers Spirit and Opportunity.

A flower is on a piece of aerogel which is suspended over a Bunsen burner. Aerogel has excellent insulating properties, and the flower is protected from the flame (NASA)

When NASA built its Stardust spacecraft to collect dust samples from a comet, aerogels were used because their porous structure could be used to capture particles. More importantly, the use of aerogels meant that particles could be collected without being damaged in the process. Otherwise, particles would have heated up or even vaporized during the high-impact collision with the spacecraft.

Did you know? Aerogels currently have commercial applications on Earth too, like refrigeration and clothing. Mountain climbers have used insoles made with aerogels to prevent heat loss or gain.Aside from being excellent insulators, aerogels also have unique mechanical properties that scientists are now beginning to explore. Traditional aerogels made from silica break and crumble easily. But the next generation of aerogels being developed by NASA are thin, flexible, and up to 500 times stronger than traditional silica-based aerogels. Inch-for-inch, they provide up to 12 times more insulation than fibreglass. NASA scientists unveiled these new aerogels at a recent conference.

Scientists are still working on the chemical stability of the new aerogels, but they see strong potential for future aerospace applications like insulation for vehicles used in planetary entry, descent, and landing. Previous Mars rovers were protected by hard aeroshell heat shields, but future space exploration vehicles will likely be more complex and heavier, requiring larger aerodynamic decelerators. The new, more flexible aerogels could be made into inflatable insulation that is packed away at the start of a mission and later deployed into light-weight heat shields or decelerators.

Learn More!

Aerogels Insulate Against Extreme Temperatures (NASA) Polymer Aerogels Provide Insulation For Earth And Space (Chemical & Engineering News) Aerogel--From Aerospace to Apparel (NASA Spinoff) New space-age insulating material for homes, clothing and other everyday uses (American Chemical Society) The Pioneer: Samuel Kistler (Microstructured Materials Group, Lawrence Berkeley National Laboratory) Size of the Nanoscale (United States National Nanotechnology Initiative) Aerogels: Thinner, Lighter, Stronger (NASA)

Other References

Brady, J. E., and J.R. Holum. 1996. Chemistry: The study of matter and its changes, p. 559. J. Wiley, New York, NY. Jones, S.M. and J. Sakamoto. 2011. Applications of Aerogels in Space Exploration, p. 721-746. In M.A. Aegerter, N. Leventis, and M.M. Koebel (ed.), Aerogels Handbook. Meador, M.A. et al. 2012. Mechanically Strong, Flexible Polyimide Aerogels Cross-Linked with Aromatic Triamine. ACS Applied Materials and Interfaces. 4: 536-544. Nappi, E. 1998. Aerogel and its applications to rich detectors. ICFA Instrumentation Bulletin. 17. [Online.]

Catherine Chan

An aspiring science writer with a master's in materials science engineering from the University of Toronto.

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