Space travel will be cheap

Freeman Dyson : physicist, mathematician
Space travel will be cheap. "No law of physics or biology forbids cheap travel and settlement all over the solar system and beyond. But it is impossible to predict how long this will take. Predictions of the dates of future achievements are notoriously fallible. My guess is that the era of cheap unmanned missions will be the next fifty years, and the era of cheap manned missions will start sometime late in the twenty-first century.
Any affordable program of manned exploration must be centered in biology, and its time frame tied to the time frame of biotechnology; a hundred years, roughly the time it will take us to learn to grow warm-blooded plants, is probably reasonable".

Dyson, FJ, "Warm-blooded plants and freeze-dried fish: the future of space exploration. Played" The Atlantic Monthly, November 1997