[00:01.55]Lesson 35
[00:03.49]Space odyssey
[00:12.30]When will it be possible for us to think seriously about colonising Mars?
[00:19.69]The Moon is likely to become the industrial hub of the Solar System supplying the rocket fuels for its ships,
[00:27.91]easily obtainable from the lunar rocks in the form of liquid oxygen.
[00:33.59]The reason lies in its gravity.
[00:36.49]Because the Moon has only an eightieth of the Earth's mass,
[00:40.86]it requires 97% less energy
[00:44.05]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!
[00:53.22]This may sound fantastic, but it is easily calculated.
[00:58.20]To escape from the Earth in a rocket, one must travel at seven miles per second.
[01:04.38]The comparable speed from the Moon is only 1.5 miles per second.
[01:10.68]Because the gravity on the Moon's surface is only a sixth of Earth's (remember how easily the Apollo astronauts bounded along),
[01:19.48]it takes much less energy to accelerate to that 1.5mps than it does on Earth.
[01:27.36]Moon dwellers will be able to fly in space at only three percent of the cost of similar journeys by their terrestrial cousins.
[01:36.69]Arthur C.Clark once suggested a revolutionary idea passes through three phases:
[01:43.13]1.  'It's impossible--don't waste my time.'
[01:47.69]2.  'It's possible, but not worth doing.'
[01:53.00]3.  'I said it was a good idea all along.'
[01:58.78]The idea of colonising Mars--a world 160 times more distant than the Moon--will move decisively from the second phase to the third,
[02:09.19]when a significant number of people are living permanently in space.
[02:14.41]Mars has an extraordinary fascination for would-be voyagers.
[02:19.02]America, Russia and Europe are filled with enthusiasts--many of them serious and senior scientists who dream of sending people to it.
[02:30.55]Their aim is understandable.
[02:33.94]It is the one world in the Solar System that is most like the Earth.
[02:38.93]It is a world of red sandy deserts (hence its name--the Red Planet),
[02:45.03]cloudless skies, savage sandstorms, chasms wider than the Grand Canyon and at least one mountain more than twice as tall as Everest.
[02:56.38]It seems ideal for settlement.