Originating Technology/NASA Contribution
Launching the space shuttle involves an interesting paradox: While the temperatures inside the shuttle’s main engines climb higher than 6,000 °F— hot enough to boil iron—for fuel, the engines use liquid hydrogen, the second coldest liquid on Earth after liquid helium.
Maintained below 20 K (-423 °F), the liquid hydrogen is contained in the shuttle’s rust-colored external tank. The external tank also contains liquid oxygen (kept below a somewhat less chilly 90 K or -297 °F) that combines with the hydrogen to create an explosive mixture that—along with the shuttle’s two, powdered aluminum-fueled solid rocket boosters—allows the shuttle to escape Earth’s gravity.
The cryogenic temperatures of the main engines’ liquid fuel can cause ice, frost, or liquefied air to build up on the external tank and other parts of the numerous launch fueling systems, posing a possible debris risk when the ice breaks off during launch and causing difficulties in the transfer and control of these cryogenic liquid propellants. Keeping the fuel at the necessary ultra-cold temperatures while minimizing ice buildup and other safety hazards, as well as reducing the operational maintenance costs, has required NASA to explore innovative ways for providing superior thermal insulation systems. To address the challenge, the Agency turned to an insulating technology so effective that, even though it is mostly air, a thin sheet can prevent a blowtorch from igniting a match.
Aerogels were invented in 1931 and demonstrate properties that make them the most extraordinary insulating materials known; a 1-inch-thick piece of aerogel provides the same insulation as layering 15 panes of glass with air pockets in between. Derived from silica, aluminum oxide, or carbon gels using a supercritical drying process—resulting in a composition of almost 99-percent air—aerogels are the world’s lightest solid (among 15 other titles they hold in the Guinness World Records), can float indefinitely on water if treated to be hydrophobic, and can withstand extremely hot temperatures (from 1,100 °F to 3,000 °F depending on the type of aerogel) down to cryogenic levels, making this “frozen smoke” ideal for use in space. Because of its low weight and ability to withstand temperature extremes, an aerogel was even used as the space-based catcher’s mitt to trap comet particles and space dust for NASA’s Stardust mission, launched in 1999.
All of this remarkable technology’s characteristics were ideal for NASA’s purposes except one: The aerogels were extremely brittle. Through a long-term partnership between Kennedy Space Center and Aspen Aerogels Inc., of Northborough, Massachusetts, researchers developed a flexible, durable form of aerogel that NASA has since used as cryogenic insulation for space shuttle launch systems. Through Aspen Aerogels, the technology has made oil pipeline insulation, extreme weather clothing, and infrared shielding for combat helicopters.
Aspen Aerogels, which developed the “R&D 100” award-winning flexible aerogels under Small Business Innovation Research (SBIR) contracts with Kennedy, approached Acoustiblok Inc., of Tampa, Florida, to perform acoustical testing on its Spaceloft flexible aerogel to explore the potential for enhancing the aerogel’s sound-muffling capabilities. Acoustiblok is an industry leader in acoustical insulation (one-eighth of an inch of Acoustiblok, the company’s proprietary acoustical insulation, reduces more sound than 12 inches of concrete when added to a stud wall) and has previously conducted research with NASA on floor resonance—reducing sound from one floor of a building to the next. Impressed by the aerogel’s qualities, Acoustiblok considered aerogel products for enhancing energy efficiency that could take advantage of the company’s expertise in providing sound insulation for buildings and other applications.