Man must at all costs overcome the Earth's gravity and have, in reserve, the space at least of the Solar System.
– Konstantin Tsiolkovsky
Mankind will not forever remain on Earth, but in the pursuit of light and space will first timidly emerge from the bounds of the atmosphere, and then advance until he has conquered the whole of circumsolar space.
– Konstantin Tsiolkovsky
The Earth is the cradle of humanity, but mankind cannot stay in the cradle forever.