633. The Moon is likely to become the industrial hub of the Solar System, supplying the rocket fuels fro its ships, easily obtainable from the lunar rocks in the from of liquid oxygen.
634. The reason lies in its gravity.
635. Because the Moon has only an eightieth of the Earth's mass,
636. 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!
637. This may sound fantastic, but it is easily calculated.
638. To escape from the Earth in a rocket, one must travel at seven miles per second.
639. The comparable speed from the Moon is only 1.5 miles per second.
640. Because the gravity on the Moon's surface is only a sixth of Earth's (remember how easily the Apollo astronauts bounded along),
由于月球表面的重力仅是地球表面的1/6 -- 还记得阿波罗飞船中的宇航员累松地跳跃 --
641. it takes much less energy to accelerate to that 1.5 miles per second than it does on Earth.
642. Moon-dwellers will be able to fly in space at only three per cent of the cost of similar journeys by their terrestrial cousins.
643. Arthur C. Clark once suggested a revolutionary idea passes through three phases:
644. 'It's impossible -- don't waste my time.'
645. 'It's possible, but not worth doing.'
646. 'I said it was a good idea all along.'
647. The idea of colonising Mars -- a world 160 times more distant time the Moon -- will move decisively from the second phase to the third, when a significant number of people are living permanently in space.
如果有相当数量的人永久性地住在太空，征服火星的计划 -- 一个比月球远160倍的星球 -- 就可以明确地从第2阶段进入第3阶段。
648. Mars has an extraordinary fascination for would-be voyagers.
649. America, Russia and Europe are filled with enthusiasts -- many of them serious and senior scientists -- who dream of sending people to it.
美国、俄罗斯和欧洲都有许多热心此项事业的人 -- 其中的不少是认真和资深的科学家，他们一直梦想着把人送上火星。
650. Their aim is understandable.
651. It is the one world in the Solar System that is most like the Earth.
652. It is a world of red sandy deserts (hence its name -- the Red Planet), cloudless skies, savage sandstorms, chasms wider than the Grand Canyon and at least one mountain more than twice as tall as Everest.
653. It seems ideal for settlement.