相比之下，火箭的化学能功率是推进力的一半乘以排气速度。

By comparison, the chemical power generated by a rocket equals one half the thrust times the exhaust velocity.

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但其排气速度却异常惊人，大约为化学燃料火箭的十倍—这使得离子推进器的效率非常高。

The exhaust velocity, though, is enormous—more than ten times that of a chemical rocket—and this makes ion propulsion extremely efficient.

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从理论上证明：对这两类发动机的两相喷管流动特性可以通过一个共同的组合参数——当量排气速度来进行分析；

Theoretically, it is proved that for both these engines, the properties of two-phase flow in nozzle can be analysed with a common combined parameter which is equivalent to exhaust velocity.

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