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[求助]
求大神们拯救一下小弟吧
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In 1999 the Stardust Mission spacecraft was launched from the Kennedy Space Center, beginning a five year journey to rendezvous with the comet Wild2 to collect particles from the comet in a grid of aerogel blocks [1, 2]. The mission design was based on the fact that aerogel is capable of stopping hypervelocity particles while keeping the particles largely intact [3]. This capability is based on the extremely porous nature of aerogels. Their porosity is due to the fact that the material is composed of myriad nano-scale filaments bonded in random orientations. As hypervelocity particles travel through the aerogel network, they destroy the filaments that constitute the network. In doing so, they convert their kinetic energy to thermal and mechanical energy and eventually stop [4, 5]. Numerous impact tests in light gas gun facilities were used to establish this capability and to quantify the results [3, 6, 7]. For the Stardust Mission, two grids of aerogel blocks were assembled: one for capturing particles from the comet during the comet encounter and another for capturing interstellar grains during the cruise phase of the mission while traveling to the comet. The two grids were mounted back-to-back and each of the grids held 132 blocks of aerogel that had been specially developed and produced for this mission. During the cruise phase, the grids were deployed for extended periods of time such that the aerogel for capturing the interstellar grains was facing the direction of the interstellar stream. After each of the interstellar grain collection periods, the grids were stowed in the sample return capsule. As the comet encounter approached, the grids were redeployed and the spacecraft was oriented such that the aerogel for capturing the cometary particles was facing the incoming stream of cometary particles. |
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2楼2015-04-12 00:27:31