At present, the launch of satellite, space shuttle and airship is based on the power which is produced by rocket.It is expensive and not safe.Moreover, it cannot produce thrust powerful enough.
英
美
释义
目前人造卫星、宇宙飞船,航天飞机等均靠火箭为推力,送人造天体经过地球大气层而进入太空中去,这样费用贵,不安全,又难能产生大推力,送大天体上太空。
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