“罗老”号二级火箭的第一级由俄罗斯设计并建造，第二级由韩国负责。
The first stage of the two-stage Naro rocket was designed and built by Russia and the second by South Korea.
当达到182公里高度时，第二级火箭自动脱落，速度达到每秒68公里。
When reached 182 km, second stage rocket off automatically, reach a speed of 68 kilometers per second.
本文考虑二级火箭在实际允许区域内的最佳质量比问题，得到解的解析表达式。
On the optimum mass ratios of two-stage rocket in the practical permissible region, we get the results analytic expression.
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