练习材料：
[Day 1790 2019-08-21]
Lesson 35-1 Space odyssey
The Moon is likely to become the industrial hub of the Solar System, supplying the
rocket fuels for its ships, easily obtainable from the lunar rocks in the form of liquid
oxygen. The reason lies in its gravity. Because the Moon has only an eightieth of the
Earth's mass, it requires 97 per cent less energy to travel the quarter of a million miles
from the Moon to Earth-orbit than the 200 mile-journey from Earth's surface into orbit!
This may sound fantastic, but it is easily calculated. To escape from the Earth in a
rocket, one must travel at seven miles per second. The comparable speed from the Moon
is only 1.5 miles per second.、
任务配置：L0+L1+L4
知识笔记：
odyssey n. 艰苦的跋涉; 漫长而充满风险的历程;
hub n. (某地或活动的) 中心，核心; 轮毂;
orbit n. (天体等运行的) 轨道; (人、组织等的) 影响范围，势力范围; v. 沿轨道运行; 围绕…运动;
练习感悟：
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