The Earth is the cradle of Humanity. But one doesn't always live in the cradle.

Consider a cask filled with a highly compressed gas. If we open one of its taps the gas will escape through it in a continuous flow, the elasticity of the gas pushing its particles into space will continuously push the cask itself. The result will a continuous change in the motion of the cask. Given a sufficient number of taps (say, six), we would be able to regulate the outflow of the gas as we liked and the cask (or sphere) would describe any curved line in accordance with any law of velocities.

All our knowledge - past, present, and future - is nothing compared to what we will never know.

For me, a rocket is only a means--only a method of reaching the depths of space--and not an end in itself... There's no doubt that it's very important to have rocket ships since they will help mankind to settle elsewhere in the universe. But what I'm working for is this resettling... The whole idea is to move away from the Earth to settlements in space.

The Earth is the cradle of Humanity. But one doesn't always live in the cradle.

A planet is the cradle of mind, but one cannot live in a cradle forever.

Man must at all costs overcome the Earth's gravity and have, in reserve, the space at least of the Solar System.