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A rocket must withstand the strong forces during launch and be as light as possible. For the main frame most rockets use aerospace grade aluminum or titanium since both metals are very strong but light weight. Future rocket designs are even looking into using carbon composite structures. Aluminum, however, melts at the high reentry temperatures. So, if a rocket needs to come back to Earth (like the Space Shuttle), heat shield tiles are made up of silica fibers since they are great insulators. These fibers are then coated by glass to increase their effectiveness.