液态燃料火箭不断得到改进，它用在飞行器上，也被用来研究高层大气和把地球卫星送入轨道。
The liquid fuel rocket, which is continually being improved, is used in aircraft as well as for research in the upper air and for putting earth satellites into orbits.
然而我的理解是，“混合动力”火箭引擎同时使用固体燃料和液态或气态推进剂。
However, from what I gather, "hybrid" rocket engines use both solid and liquid or gas propellants.
固体燃料火箭发动机的构造更简单、分量更轻，而且相对更安全。 在固体燃料火箭发动机里，燃料和氧化剂被预先混合成稳定的液态推进剂，然后被塞满火箭发动机的燃料箱里。
Solid-fuel rockets, in which the fuel and oxidiser are pre-mixed into a stable, solid propellant and then packed inside the case of the rocket, are simpler, lighter and relatively safer.
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