The greatest gain from space travel consists in the extension of our knowledge. In a hundred years this newly won knowledge will pay huge and unexpected dividends.

Can a physicist visualize an electron? The electron is materially inconceivable and yet, it is so perfectly known through its effects that we use it to illuminate our cities, guide our airlines through the night skies and take the most accurate measurements. What strange rationale makes some physicists accept the inconceivable electrons as real while refusing to accept the reality of a Designer on the ground that they cannot conceive Him?

The logistic requirements for a large, elaborate mission to Mars are no greater that those for a minor military operation extending over a limited theatre of war.

I believe that the time has arrived for medical investigation of the problems of manned rocket flight, for it will not be the engineering problems but rather the limits of the human frame that will make the final decision as to whether manned space flight will eventually become a reality.

To simply dismiss the concept of God as being unscientific is to violate the very objectivity of science itself.

I have learned to use the word 'impossible' with the greatest caution.

There are flying grandfathers. But I intend to be an orbiting grandfather.