Looking sharp

 作者:仇嘈     |      日期:2019-03-08 07:02:03
By Charles Seife in Washington DC AS IT returns to Earth, the space shuttle flies with all the grace of a winged brick. But the spaceplanes of tomorrow should be a pilot’s dream, now that NASA’s advisers are urging the agency to step up its research into a new class of heat-tolerant materials. The materials should also bring dramatic reductions in fuel costs. The shuttle isn’t terribly aerodynamic because its nose and wing tips must be thick—so that a shock wave forms in front of the craft, protecting it from some of the friction of re-entry. Any thinner, and the shuttle would get dangerously hot. But a team at NASA’s Ames Research Center in Moffett Field, California, has created a new class of ceramics based on the metals hafnium and zirconium that can withstand repeated exposures to 2400 °C (see “Breaking the heat barrier”, New Scientist, 30 August 1997, p 28). The shuttle’s protective tiles begin to burn at 1400 °C. The new materials should allow the leading edges of future spaceplanes’ wings and noses to be built with radii of just a few millimetres. “You can make space vehicles look like supersonic aircraft,” says Dan Rasky, a member of the Ames team. This will bring real improvements in handling and efficiency: spacecraft could fly like planes on both ascent and descent, instead of blasting up like rockets and falling down like inefficient gliders. This would greatly reduce fuel costs. Spacecraft designers are thrilled. “I can’t say good enough things about it,” says Preston Carter of the Lawrence Livermore National Laboratory in California. He has incorporated the materials into his designs for the Hypersoar, a spaceplane planned to skip across the top of the atmosphere at ten times the speed of sound. NASA’s Advisory Council shares Carter’s enthusiasm,