Finite element analysis of silica aerogel to be used in high-temperature insulation tiles for next generation space shuttle

For more than fifty years man has been venturing into space. For space missions heat became more important because the velocity needed to maintain orbit or the velocity needed to travel to the moon and back was much higher than that of previous low Earth orbit missions. This velocity during reentry causes the air molecules in the upper atmosphere break apart and create electrically charged plasma that surround the space craft. Temperatures from this electrically charged plasma can reach as high as 1260°C on the leading edge of the craft. The fuselage of the space vehicle and the people inside must be protected from this reentry heat, and thus the need for heat shielding. Originally heat shielding was accomplished by coating the leading surface of the reentry vehicle with a material design to burn off during reentry and dissipate energy. The burned material charred to the reentry vehicle to form a protective coating which blocked heat penetration beyond the outer surface. Later generations of space craft began using reusable heat shielding to avoid the loss of material during reentry and provide better heat shielding. The tiles used on the now retired space shuttle are a combination of a low density, high-purity silica 99.8% amorphous fiber insulation made rigid by a reaction cured glass. This heat shielding system proved to be very affective for protecting the space shuttle from the intense heat of reentry. The high-purity silica insulation provided a very low thermal conductivity, as low as 0.0485W/m°C at room temperature and raises to 0.126W/m°C at 1100°C. While the ceramic reaction cured glass provides the structural rigidity and the impact protection from debris while in orbit. Since this thermal protection system has been implemented, there have been advances in the field of thermal insulation, for instance silica aerogel. Invented in the 1930's aerogels are an exotic class of material with very remarkable and useful properties. Aerogels are some of the lightest weight and lowest density solid material known. Pure aerogels also have an extremely low coefficient of thermal conductivity with an index of refraction close to that of a vacuum or air making aerogels some of the best thermal insulators currently available today. The biggest disadvantage to silica aerogel is its fragility. In recent years a new manufacturing technique began introducing crosslinking molecules into the aerogel structure making it slightly denser but much stronger and more of a viable option for a variety of applications. Cross linked silica aerogels are strong enough to be coated, cut, machined, drilled and attached to surfaces, making it useful to serve as a thermal insulator in the harsh operating conditions experienced by a spacecraft in space and reentering the Earth's atmosphere. In comparison with the silica matrix, silica aerogel exhibits 0.25 W/m°C at 22°C increasing to 0.038 W/m at 527°C. By using finite element analysis, it was determined that the silica aerogel has a heat propagation of only 66% that of the existing tiles, netting 33% better insulating than the silica matrix at less than 30% the weight.