Periodic orbits

His fantasies are no longer science-fiction and the astronauts of our day travel round the world in 86 minutes, not 80 days. We are now going to describe what might happen on an imaginary journey by space-ship, yet this imaginary journey will become possible in fewer decades than the time it took to contract Jules Verne's crazy notion of a journey round the world in 80 days to a lightning journey of 86 minutes. But let us not think in terms of such short periods of time! Let us assume that our space-ship will leave the earth for an unknown distant sun in 150 years' time. The space-ship would be as big as a present-day ocean liner and would therefore have a launching weight of about 100,000 tons with a fuel load of 99,800 tons, i.e. an effective pay load of less than 200 tons. Impossible? Already we could assemble a space-ship piece by piece while in orbit round a planet. Yet even this assembly work will become unnecessary in less than two decades, because it will be possible to prepare the giant space-ship for launching on the moon ...»