Lesson 35
Space odyssey
太空探索
First listen and then answer the following question.
听录音,然后回答以下问题。
When will it be possible for us to think seriously about colonising Mars?
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. 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. Because the gravity on the Moon's surface is only a sixth of Earth's (remember how easily the Apollo astronauts bounded along), it takes much less energy to accelerate to that 1.5 miles per second than it does on Earth. Moon-dwellers will be able to fly in space at only three per cent of the cost of similar journeys by their terrestrial dwellers will be able to fly in space at only three per cent of the cost of similar journeys by their terrestrial cousins.
Arthur C. Clark once suggested a revolutionary idea passes through three phases:
1 'It's impossible -- don't waste my time.'